SHOW COLUMNS FROM `GA_ACCOUNTS_MT` LIKE 'user_id%';

SELECT  TABLE_TYPE,table_schema AS DBName,TABLE_NAME AS TABLE_NAME, 

table_rows AS QuantofRows, 

ROUND((data_length + index_length) /1024, 2 ) AS "DB Size in KB"  ,

ROUND((data_length + index_length) / 1024 / 1024, 1) AS "DB Size in MB" 

FROM information_schema.TABLES

 WHERE   table_schema = 'GOAUDITS' 

AND TABLE_TYPE='BASE TABLE'  AND TABLE_NAME LIKE 'GA_AUD%'

/*

IN ('GA_QUESTION_MT','GA_QUESTION_DT',

'GA_QUESTION_SCORE_MT',

'GA_QUESTION_SCORE_MT_TEMP',

'GA_QUESTIONPHOTO_MT',

'GA_QUEST_MULTICHOICE_DT',

'GA_QUESCHSMAP_TP',

'GA_QUESCONFIG_TP',

'GA_QUEST_ACTIONPLAN_DT',

'GA_QUEST_ACTIONPLAN_DT_ACT',

'GA_QUEST_MULTICHOICE_DT',

'GA_QUESTACTIONFIELDS_MT',

'GA_QUESTACTIONFIELDS_DT',

'GA_QUESTIMG_DT',

'GA_QUESTION_MT_PARENT_ZERO',

'GA_QUESTION_MT_TEMP'

)

*/

 -- AND (TABLE_NAME LIKE 'GA_AUD%'   OR  TABLE_NAME LIKE 'GA_QUE%' or TABLE_NAME LIKE  'GA_USE%' or TABLE_NAME LIKE  'GA_STORE%' or TABLE_NAME LIKE  'GA_CLI%')

ORDER BY TABLE_NAME DESC, (data_length + index_length) DESC; 

MYSQL TIPS:

--COPY TABLE FROM ONE DB TO ANOTHER

CREATE TABLE GA_LICENSE_MT AS SELECT * FROM GOAUDITS.GA_LICENSE_MT 

--SCHEMA DETAILS

SELECT 'mysql' dbms,t.TABLE_SCHEMA,t.TABLE_NAME,c.COLUMN_NAME,c.ORDINAL_POSITION,c.DATA_TYPE,c.CHARACTER_MAXIMUM_LENGTH,n.CONSTRAINT_TYPE,k.REFERENCED_TABLE_SCHEMA,k.REFERENCED_TABLE_NAME,k.REFERENCED_COLUMN_NAME FROM INFORMATION_SCHEMA.TABLES t LEFT JOIN INFORMATION_SCHEMA.COLUMNS c ON t.TABLE_SCHEMA=c.TABLE_SCHEMA AND t.TABLE_NAME=c.TABLE_NAME LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE k ON c.TABLE_SCHEMA=k.TABLE_SCHEMA AND c.TABLE_NAME=k.TABLE_NAME AND c.COLUMN_NAME=k.COLUMN_NAME LEFT JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS n ON k.CONSTRAINT_SCHEMA=n.CONSTRAINT_SCHEMA AND k.CONSTRAINT_NAME=n.CONSTRAINT_NAME AND k.TABLE_SCHEMA=n.TABLE_SCHEMA AND k.TABLE_NAME=n.TABLE_NAME 

WHERE t.TABLE_TYPE='BASE TABLE' AND t.TABLE_SCHEMA IN('AUDITS')

---DB SIZE

SHOW COLUMNS FROM `GA_ACCOUNTS_MT` LIKE 'user_id%';

SELECT  TABLE_TYPE,table_schema AS DBName,TABLE_NAME AS TABLE_NAME, 

table_rows AS QuantofRows, 

ROUND((data_length + index_length) /1024, 2 ) AS "DB Size in KB"  ,

ROUND((data_length + index_length) / 1024 / 1024, 1) AS "DB Size in MB" 

FROM information_schema.TABLES

 WHERE   table_schema = 'GOAUDITS' 

AND TABLE_TYPE='BASE TABLE'  AND TABLE_NAME LIKE 'GA_AUD%'

how to split comma separated values into Rows on Mysql

how to split comma separated values into Rows on Mysql

This procedure will split  a “;” separated column in to new fields preserving ids.

This is very specific problem, lets check it with example.

Consider a sample table test:




And we want output as follows:




So again I wrote a procedure.

Procedure will read a data from “tmp” table and will split data by my_delimiter delimiter and generate a temporary table.

You may alter it as per requirement.

------------------------------------------------------------------------------------

DELIMITER $$

DROP PROCEDURE IF EXISTS `split_string` $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `split_string`()
BEGIN

DECLARE my_delimiter CHAR(1);
DECLARE split_string varchar(255);
DECLARE done INT;
DECLARE occurance INT;
DECLARE i INT;
DECLARE split_id INT;
DECLARE ins_query VARCHAR(500);
DECLARE splitter_cur CURSOR FOR
SELECT id,cat from tmp;

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;

DROP TEMPORARY TABLE IF EXISTS `my_splits`;
CREATE TEMPORARY TABLE `my_splits` (
  `splitted_column` varchar(45) NOT NULL,
  `id` int(10) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;


OPEN splitter_cur;
splitter_loop:LOOP
      FETCH splitter_cur INTO split_id,split_string;

SET occurance=length(split_string)-length(replace(split_string,';',''))+1;
SET my_delimiter=';';
  IF done=1 THEN
    LEAVE splitter_loop;
  END IF;
#  select occurance;
  IF occurance > 0 then
    #select occurance;
    set i=1;
    while i <= occurance do
#        select concat("SUBSTRING_INDEX(SUBSTRING_INDEX( '",split_string ,"', '",my_delimiter,"', ",i, "),'",my_delimiter,"',-1);");
        SET ins_query=concat("insert into my_splits(splitted_column,id) values(", concat("SUBSTRING_INDEX(SUBSTRING_INDEX( '",split_string ,"', '",my_delimiter,"', ",i, "),'",my_delimiter,"',-1),",split_id,");"));
#    select ins_query;
        set @ins_query=ins_query;
        PREPARE ins_query from @ins_query;
        EXECUTE ins_query;
      set i=i+1;
    end while;
  ELSE
        set ins_query=concat("insert into my_splits(splitted_column,id) values(",split_string,"',",split_id,");");
        set @ins_query=ins_query;
        PREPARE ins_query from @ins_query;
        EXECUTE ins_query;
  END IF;
  set occurance=0;
END LOOP;

CLOSE splitter_cur;

END $$

DELIMITER ;

How to estimate SQL query timing?

How to estimate SQL query timing?

MySQL has a profiling tool. When you open a MySQL session, you could set the variable "profiling" to 1 or ON.
  

mysql> SET profiling = 1;

So, all the statements sent to the server will be profiled and stored in a historical and shown later with the command:

mysql> SHOW PROFILES;

See, from MySQL manual:

mysql> SET profiling = 1;
Query OK, 0 rows affected (0.00 sec)

mysql> DROP TABLE IF EXISTS t1;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE TABLE T1 (id INT);
Query OK, 0 rows affected (0.01 sec)

mysql> SHOW PROFILES;
+----------+----------+--------------------------+
| Query_ID | Duration | Query                    |
+----------+----------+--------------------------+
|        0 | 0.000088 | SET PROFILING = 1        |
|        1 | 0.000136 | DROP TABLE IF EXISTS t1  |
|        2 | 0.011947 | CREATE TABLE t1 (id INT) |
+----------+----------+--------------------------+
3 rows in set (0.00 sec)

mysql> SHOW PROFILE;
+----------------------+----------+
| Status               | Duration |
+----------------------+----------+
| checking permissions | 0.000040 |
| creating table       | 0.000056 |
| After create         | 0.011363 |
| query end            | 0.000375 |
| freeing items        | 0.000089 |
| logging slow query   | 0.000019 |
| cleaning up          | 0.000005 |
+----------------------+----------+
7 rows in set (0.00 sec)

mysql> SHOW PROFILE FOR QUERY 1;
+--------------------+----------+
| Status             | Duration |
+--------------------+----------+
| query end          | 0.000107 |
| freeing items      | 0.000008 |
| logging slow query | 0.000015 |
| cleaning up        | 0.000006 |
+--------------------+----------+
4 rows in set (0.00 sec)

mysql> SHOW PROFILE CPU FOR QUERY 2;
+----------------------+----------+----------+------------+
| Status               | Duration | CPU_user | CPU_system |
+----------------------+----------+----------+------------+
| checking permissions | 0.000040 | 0.000038 |   0.000002 |
| creating table       | 0.000056 | 0.000028 |   0.000028 |
| After create         | 0.011363 | 0.000217 |   0.001571 |
| query end            | 0.000375 | 0.000013 |   0.000028 |
| freeing items        | 0.000089 | 0.000010 |   0.000014 |
| logging slow query   | 0.000019 | 0.000009 |   0.000010 |
| cleaning up          | 0.000005 | 0.000003 |   0.000002 |
+----------------------+----------+----------+------------+

How to Install MySQL 8.0 (on Windows, Mac OS X, Ubuntu) and Get Started with SQL Programming

TABLE OF CONTENTS

1.  Introduction to Relational Database and SQL

1.1  Relational Databases

1.2  Structure Query Language (SQL)

1.3  SQL By Examples

2.  Introduction to MySQL Relational Database Management System (RDBMS)

3.  How to Install MySQL 8.0 and Get Started with SQL Programming

3.1  Step 0: Create a directory to keep all your works

3.2  Step 1: Download and Install MySQL

3.3  Step 3: Start the "Server"

3.4  Step 4: Start a "Client"

3.5  Step 5: Change the Password for the Superuser "root"

3.6  Step 6: Create a New User

3.7  Step 7: Create a new Database, a new Table in the Database, Insert Records, Query and Update

3.8  More Exercises

4.  Many-to-many Relationship

5.  (Optional) Backup and Restore Databases

5.1  Backup via "mysqldump" Utility Program

5.2  Restore via "source" command in a mysql client

6.  Summary of Frequently-Used Commands

7.  (Skip Unless...) How to Debug?

7.1  Cannot Start the MySQL Server after Installation

7.2  Cannot Start the "mysql" Client

7.3  Error Using the "mysql" Client

1.  Introduction to Relational Database and SQL

1.1  Relational Databases

A relational database organizes data in tables. A table has rows (or records) and columns (or fields). Tables are related based on common columns to eliminate data redundancy and ensure data integrity.

Popular Relationship Database Management System (RDBMS) includes the commercial Oracle, IBM DB2, Microsoft SQL Server and Access, SAP SyBase Teradata; and the open-source MySQL, PostgreSQL, Embedded Apache Derby (Java DB), mSQL (mini-SQL), SQLite and Apache OpenOffice's Base.

1.2  Structure Query Language (SQL)

A high-level programming language, called Structure Query Language (SQL), is designed for interacting with the relational databases. SQL defines a set of commands, such as SELECT, INSERT, UPDATE, DELETE, CREATE TABLE, DROP TABLE, and etc.

Edgar F. Codd of IBM proposed the Relational Database Model in 1970. SQL, one of the earlier programming language, was subsequently developed by Donald D. Chamberlin and Raymond F. Boyce at IBM in the early 1970s. Oracle, subsequently, took it to a new height.

ANSI (American National Standard Institute) established the first SQL standard in 1986 (SQL-86 or SQL-87) - adopted by ISO/IEC as "ISO/IEC 9075" - followed in 1989 (SQL-89), 1992 (SQL-92 or SQL2), 1999 (SQL-99 or SQL3), 2003 (SQL:2003), 2006 (SQL:2006), 2011 (SQL:2011) and 2016 (SQL:2016). However, most of the database vendors have their own directs, e.g., PL/SQL (Oracle), Transact-SQL (Microsoft, SAP), PL/pgSQL (PostgreSQL).

1.3  SQL By Examples

A relational database system organizes data in the following hierarchy:

1. A relational database system contains many databases.
2. A database comprises tables.
3. A table have rows (or records) and columns (or fields).

Suppose we have a database called studentdb, a table called class101 in the database with 3 columns (id, name, gpa) and 4 rows as illustrated below. Each column has a data type. We choose: INT (integer) for column id, VARCHAR(50) (variable-length string of up to 50 characters) for name, and FLOAT (floating-point number) for gpa.

Database: studentdb
Table: class101
+-----------+--------------------+-------------+
| id (INT)  | name (VARCHAR(50)) | gpa (FLOAT) |
+-----------+--------------------+-------------+
|   1001    | Tan Ah Teck        |  4.5        |
|   1002    | Mohammed Ali       |  4.8        |
|   1003    | Kumar              |  4.8        |
|   1004    | Kevin Jones        |  4.6        |
+-----------+--------------------+-------------+

SQL (Structure Query Language) defines a set of intuitive commands (such as SELECT, INSERT, DELETE, UPDATE) to interact with relational database system.

SELECT

-- SYNTAX
SELECT column1, column2, ... FROM tableName WHERE criteria
SELECT * FROM tableName WHERE criteria
 
-- EXAMPLES
SELECT name, gpa FROM class101
   -- Select columns name and gpa from table class101.
   +--------------+------+
   | name         | gpa  |
   +--------------+------+
   | Tan Ah Teck  |  4.5 |
   | Mohammed Ali |  4.8 |
   | Kumar        |  4.8 |
   | Kevin Jones  |  4.6 |
   +--------------+------+
 
SELECT * FROM class101
   -- Select ALL columns from table class101.
   -- The wildcard * denotes all the columns.
   +------+--------------+------+
   | id   | name         | gpa  |
   +------+--------------+------+
   | 1001 | Tan Ah Teck  |  4.5 |
   | 1002 | Mohammed Ali |  4.8 |
   | 1003 | Kumar        |  4.8 |
   | 1004 | Kevin Jones  |  4.6 |
   +------+--------------+------+
 
SELECT name, gpa FROM class101 WHERE gpa >= 4.7
   -- Select columns name and gpa, where the rows meet the criteria.
   -- You can compare numbers (INT, FLOAT) using =, >, <, >=, <=, <> (!=)
   +--------------+------+
   | name         | gpa  |
   +--------------+------+
   | Mohammed Ali |  4.8 |
   | Kumar        |  4.8 |
   +--------------+------+
    
SELECT name, gpa FROM class101 WHERE name = 'Tan Ah Teck'
   -- Full-match (= or !=) on string. Strings are enclosed in quotes.
   +-------------+------+
   | name        | gpa  |
   +-------------+------+
   | Tan Ah Teck |  4.5 |
   +-------------+------+
 
SELECT name FROM class101 WHERE name LIKE 'k%'
   -- Use "LIKE" for string pattern-matching, with
   --   wildcard % matches zero or more (any) characters;
   --   wildcard _ matches one (any) character.
   +-------------+
   | name        |
   +-------------+
   | Kumar       |
   | Kevin Jones |
   +-------------+
 
SELECT * FROM class101 WHERE gpa > 4 AND name LIKE 'k%' ORDER BY gpa DESC, name ASC
   -- Use AND, OR, NOT to combine simple conditions.
   -- Order the results in DESC (descending) or ASC (Ascending)
   +------+-------------+------+
   | id   | name        | gpa  |
   +------+-------------+------+
   | 1003 | Kumar       |  4.8 |
   | 1004 | Kevin Jones |  4.6 |
   +------+-------------+------+

DELETE

-- SYNTAX
DELETE FROM tableName WHERE criteria
 
-- EXAMPLES
DELETE FROM class101
  -- Delete ALL rows from the table class101! Beware that there is NO UNDO!
DELETE FROM class101 WHERE id = 33
  -- Delete rows that meet the criteria.

INSERT

-- SYNTAX
INSERT INTO tableName VALUES (firstColumnValue, ..., lastColumnValue)       -- All columns
INSERT INTO tableName (column1, column2, ...) VALUES (value1, value2, ...)  -- Selected Columns
 
-- Example
INSERT INTO class101 VALUES (1001, 'Tan Ah Teck', 4.5)
  -- List value of all columns.
INSERT INTO class101 (name, gpa) VALUES ('Peter Jones', 4.55)
  -- Missing fields will be set to their default values or NULL

UPDATE

-- SYNTAX
UPDATE tableName SET column = value WHERE criteria
 
-- EXAMPLES
UPDATE class101 SET gpa = 5.0                                  -- ALL rows
UPDATE class101 SET gpa = gpa + 1.0 WHERE name = 'Tan Ah Teck' -- Selected rows

CREATE TABLE

-- SYNTAX
CREATE TABLE tableName (column1Name column1Type, column2Name column2Type, ...)
 
-- EXAMPLES
CREATE TABLE class101 (id INT, name VARCHAR(50), gpa FLOAT)

DROP TABLE

-- SYNTAX
DROP TABLE tableName
 
-- EXAMPLES
DROP TABLE class101  -- Delete the table. Beware that there is No UNDO!!!

Notes:

1. Case Sensitivity: SQL keywords, names (identifiers), strings may or may not be case-sensitive, depending on the implementation.
   • In MySQL, the keywords are NOT case-sensitive. For clarity, I show the keywords in UPPERCASE in this article.
   • For programmers, it is BEST to treat the names (identifiers) and strings as case-sensitive. 
     (In MySQL, column-names are always case insensitive; but table-names are case-sensitive in Unix, but case-insensitive in Windows (confused!!). Case-sensitivity in string comparison depends on the collating sequence used (?!).)
2. String: SQL strings are enclosed in single quotes. But most implementations (such as MySQL) accept both single and double quotes.

2.  Introduction to MySQL Relational Database Management System (RDBMS)

SQL is a programming language for interacting with relational databases. On the other hand, MySQL is a software system - a Relational Database Management System.

MySQL is one of the most used, industrial-strength, open-source and free Relational Database Management System (RDBMS). MySQL was developed by Michael "Monty" Widenius and David Axmark in 1995. It was owned by a Swedish company called MySQL AB, which was bought over by Sun Microsystems in 2008. Sun Microsystems was acquired by Oracle in 2010.

MySQL is successful, not only because it is free and open-source (there are many free and open-source databases, such as PostgreSQL, Apache Derby (Java DB), mSQL (mini SQL), SQLite and Apache OpenOffice's Base), but also for its speed, ease of use, reliability, performance, connectivity (full networking support), portability (run on most OSes, such as Unix, Windows, Mac), security (SSL support), small size, and rich features. MySQL supports all features expected in a high-performance relational database, such as transactions, foreign key, replication, subqueries, stored procedures, views and triggers.

MySQL is often deployed in a LAMP (Linux-Apache-MySQL-PHP), WAMP (Windows-Apache-MySQL-PHP), or MAMP (MacOS-Apache-MySQL-PHP) environment. All components in LAMP is free and open-source, inclusive of the Operating System.

The mother site for MySQL is https://www.mysql.com. The ultimate reference for MySQL is the "MySQL Reference Manual", available at https://dev.mysql.com/doc. The reference manual is huge - the PDF has over 3700 pages!!!

MySQL operates as a client-server system over TCP/IP network. The server runs on a machine with an IP address on a chosen TCP port number. The default TCP port number for MySQL is 3306. Users can access the server via a client program, connecting to the server at the given IP address and TCP port number.

3.  How to Install MySQL 8.0 and Get Started with SQL Programming

I want you to install MySQL on your own machine, because I want you to learn how to install, customize and operate complex industrial software system. Installation could be the hardest part in this exercise.

3.1  Step 0: Create a directory to keep all your works

Create a directory called "c:\myWebProject" (for Windows) or "~/myWebProject" (for Mac OS X, where "~" denotes your home directory) to keep all your works.

// For Windows: Use "C:\myWebProject"
// Launch a "CMD" and issue these commands:
c:
cd \
mkdir myWebProject

// For Mac OS X: Use "~/myWebProject" (where "~" denotes your home directory)
// Launch a "Terminal" and issue these commands:
cd
mkdir myWebProject

Use your graphical interface, e.g., File Explorer (Windows), or Finder (Mac OS X) to verify this directory. (Of course you can use your graphical interface to create this directory!)

For novices: It is important to follow this step. Otherwise, you will be out-of-sync with this article and will not be able to find your files later.

3.2  Step 1: Download and Install MySQL

For Windows

1. Download MySQL Community Server ZIP ARCHIVE from https://dev.mysql.com/downloads/mysql/:
   1. Under "General Available (GA) Releases" tab.
   2. Under "MySQL Community Server 8.0.{xx}", where {xx} is the latest update number ⇒ In "Select Operating System", choose "Microsoft Windows".
   3. Under "Other Downloads", download "Windows (x86, 64-bit), ZIP ARCHIVE (mysql-8.0.{xx}-winx64.zip)".
   4. Under "Begin your Download", there is NO need to "Login" or "Sign up" - Just click "No thanks, just start my downloads!".
2. UNZIP the downloaded file into your project directory "C:\myWebProject". MySQL will be unzipped as "c:\myWebProject\mysql-8.0.{xx}-winx64".
   For EASE OF USE, we shall shorten and rename the directory to "c:\myWebProject\mysql". Take note and remember your MySQL installed directory!!!
3. (NEW since MySQL 5.7.7) Initialize the database: Start a CMD (as administrator) ("Search" button ⇒ Enter "cmd" ⇒ Right-Click on "Command Prompt" ⇒ Run as Administrator) and issue these commands:

   // Change directory to the MySQL's binary directory
   // Suppose that your MySQL is installed in "c:\myWebProject\mysql"
   c:
   cd \myWebProject\mysql\bin
    
   // Initialize the database. Create a root user with random password. Show the messages on console
   mysqld --initialize --console
   ......
   ...... [Note] A temporary password is generated for root@localhost: xxxxxxxx

   During the installation, a superuser called root is created with a temporary password, as shown above. TAKE NOTE of the PASSWORD, COPY and save it somewhere, and TAKE A PICTURE!!!!
4. If you make a mistake or forgot your password, DELETE the entire MySQL directory "C:\myWebProject\mysql", and REPEAT step 2 and 3.

For Mac OS X

Notes: The current version of MySQL (8.0.xx) works with Mac OS 10.14 and 10.13. If you are running older version of Mac OS, you need to find an archived version of MySQL @ https://dev.mysql.com/downloads/ ⇒ Archive.

1. Download the MySQL Community Server "DMG Archive" from https://dev.mysql.com/downloads/mysql/:
   1. Under "General Available (GA) Releases" tab.
   2. Under "MySQL Community Server 8.0.{xx}", where {xx} is the latest update number ⇒ In "Select Operating System", choose the "macOS".
   3. Select the appropriate "macOS 10.14 (x86, 64-bit) DMG Archive" for macOS 10.14 or 10.13 (mysql-8.0.{xx}-macos10.14-x86_64.dmg).
      • To check your OS version ⇒ Click the 'Apple' logo ⇒ "About this Mac".
      • To check whether your Mac OS is 32-bit or 64-bit ⇒ Read http://support.apple.com/kb/ht3696. Unless you have a dinosaur-era machine, it should be 64-bit!
   4. There is NO need to "Login" or "Sign up" - Just click "No thanks, just start my download".
2. To install MySQL (See https://dev.mysql.com/doc/refman/8.0/en/osx-installation-pkg.html for screen shots):
   1. Go to "Downloads" ⇒ Double-click ".dmg" file downloaded.
   2. Double-click the "mysql-8.0.{xx}-osx-10.{xx}-x86_64.pkg".
   3. In "Introduction", click "Continue".
   4. In "License", choose "Agree".
   5. In "Installation Type", click "Install".
   6. In "Configuration", choose "Use Strong Password Encryption", and enter a password for the "root" user. Make sure you remember your password.
   7. MySQL will be installed in "/usr/local/mysql". Take note of this installed directory!!
   8. Eject the ".dmg" file.
3. If you make a mistake or forgot your password, stop the server (Click "Apple" Icon ⇒ System Preferences ⇒ MySQL ⇒ Stop). 
   Goto /usr/local (via Finder ⇒ Go ⇒ GoTo Folder ⇒ type /usr/local) and remove all the folders beginning with "mysql...", e.g., "mysql-8.0.{xx}..." and "mysql", and Re-run Step 2.

For Ubuntu

Refer to "How to install MySQL 5 on Ubuntu".

I shall assume that MySQL is installed in directory "c:\myWebProject\mysql" (for Windows) or "/usr/local/mysql" (for Mac OS X). But you need to TAKE NOTE OF YOUR MySQL INSTALLED DIRECTORY. Hereafter, I shall denote the MySQL installed directory as <MYSQL_HOME> in this article.

3.3  Step 3: Start the "Server"

The MySQL is a client-server system. The database is run as a server application. Users access the database server via a client program, locally or remotely thru the network, as illustrated:

1. The server program is called "mysqld" (with a suffix 'd', which stands for daemon - a daemon is a non-interactive process running in the background).
2. The client program is called "mysql" (without the 'd').

The programs mysqld and mysql are kept in the "bin" sub-directory of the MySQL installed directory.

Startup Server

For Windows

To start the database server, launch a new CMD shell:

-- Change the current directory to MySQL's binary directory
-- Assume that the MySQL installed directory is "c:\myWebProject\mysql"
c:
cd \myWebProject\mysql\bin
 
-- Start the MySQL Database Server
mysqld --console
......
......
XXXXXX XX:XX:XX [Note] mysqld: ready for connections.
Version: '8.0.xx'  socket: ''  port: 3306  MySQL Community Server (GPL)

Note: The --console option directs the output messages to the console. Without this option, you will see a blank screen.

For Mac OS

The EASY WAY: Via graphical control. Click "Apple" Icon ⇒ System Preferences ⇒ MySQL ⇒ Start or Stop.

The MySQL database server is now started, and ready to handle clients' requests.

Anything that can possibly go wrong, does! Read "How to Debug".

Shutdown Server

For Windows

The quickest way to shut down the database server is to press Ctrl-C to initiate a normal shutdown. DO NOT KILL the server via the window's CLOSE button.

Observe these messages from the MySQL server console:

XXXXXX XX:XX:XX [Note] mysqld: Normal shutdown
......
XXXXXX XX:XX:XX  InnoDB: Starting shutdown...
XXXXXX XX:XX:XX  InnoDB: Shutdown completed; log sequence number 0 44233
......
XXXXXX XX:XX:XX [Note] mysqld: Shutdown complete
(You may need to press ENTER to get the command prompt?!)

For Mac OS X

The EASY WAY: Via the graphical control. Click "Apple" Icon ⇒ System Preferences ⇒ MySQL ⇒ Stop.

WARNING: You should properly shutdown the MySQL server. Otherwise, you might corrupt the database and might have problems restarting it. BUT, if you encounter problem shutting down the server normally, you may kill the "mysqld" process in Task Manager (for Windows); or Activity Monitor (for Mac OS X); or System Monitor (for Ubuntu).

3.4  Step 4: Start a "Client"

Recall that the MySQL is a client-server system. Once the server is started, one or more clients can be connected to the database server. A client could be run on the same machine (local client); or from another machine over the network (remote client).

To login to the MySQL server, you need to provide a username and password. During the installation, MySQL creates a superuser called "root" with a temporary password. I hope that you have taken note of this password! (Otherwise, re-install!)

The MySQL installation provides a command-line client program called "mysql". (Recall that the server program is called "mysqld" with a suffix 'd'; the client program does not have the suffix 'd').

Let's start a command-line client with the superuser "root".

First, make sure that the server is running. See previous step to re-start the server if it has been shutdown.

For Windows

Start Another NEW CMD shell to run the client (You need to keep the CMD that run the server):

-- Change the current directory to MySQL's binary directory.
-- Assume that the MySQL is installed in "c:\myWebProject\mysql".
c:
cd \myWebProject\mysql\bin
   
-- Start a client as superuser "root" (-u), and prompt for password (-p)
mysql -u root -p
Enter password:   // Enter the root's password set during installation.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 8.0.xx
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>
-- Client started. The prompt changes to "mysql>".
-- You can now issue SQL commands such as SELECT, INSERT and DELETE.

For Mac OS

Open a NEW "Terminal" and issue these commands to start a MySQL client with superuser root:

-- Change the current directory to MySQL's binary directory.
cd /usr/local/mysql/bin
 
-- Start a client with superuser "root" (-u), and prompt for password (-p)
./mysql -u root -p
Enter password:   // Enter the root's password given during installation. You will NOT any * for maximum security
Welcome to the MySQL monitor.  Commands end with ; or \g.
......
mysql>
-- Client started. The prompt changes to "mysql>".
-- You can now issue SQL commands such as SELECT, INSERT and DELETE.

(Skip Unless...) Read "How to Debug".

3.5  Step 5: Change the Password for the Superuser "root"

As mentioned earlier, the MySQL installation creates a superuser called "root" with a temporary random password. "root" is a privileged user that can do anything, including deleting all the databases. You are required to change the root's password immediately after logging in.

Notes: If you get stuck entering a command, press Ctrl-C to abort the current command.

Changing the Password for "root"

Let's continue with our client session started earlier.

-- Change password for 'root'@'localhost'. Replace xxxx with your chosen password
-- (For macOS, there is no need to change the password, but there is no harm trying it out)
-- (For my students: use xxxx as the password. Otherwise, you will ask me what is your password next week.)
-- Take note that strings are to be enclosed by a pair of single-quotes in MySQL.
mysql> alter user 'root'@'localhost' identified by 'xxxx';
Query OK, 0 rows affected (0.00 sec)
 
-- logout and terminate the client program
mysql> quit
Bye

Re-Start a Client as "root" with the New Password

We have just changed the password for root and exited the client. Start a client and login as root again. Enter the password when prompted.

For Windows

-- Change directory to MySQL's binary directory
c:
cd \myWebProject\mysql\bin
-- Start a MySQL client
mysql -u root -p
Enter password:   // Enter the NEW password
Welcome to the MySQL monitor.
......  
mysql>
-- client started, ready to issue SQL command

For Mac OS X

-- Change directory to MySQL's binary directory
cd /usr/local/mysql/bin
-- Start a MySQL client
./mysql -u root -p
Enter password:  // Enter the NEW password
Welcome to the MySQL monitor.
......
mysql>
-- client started, ready to issue SQL command

3.6  Step 6: Create a New User

The superuser "root" is privileged, which is meant for database administration and is not meant for operational. We shall create a new user - let's call it "myuser" - with a lesser privilege. To create a new user, start a client with superuser "root":

-- Start a client, IF IT IS NOT STARTED
mysql -u root -p     // Windows
./mysql -u root -p   // Mac OS X
   
-- Create a new user called "myuser", which can login from localhost, with password "xxxx"
mysql> create user 'myuser'@'localhost' identified by 'xxxx';
Query OK (0.01 sec)
   
-- Grant permission to myuser to perform tasks
mysql> grant all on *.* to 'myuser'@'localhost';
Query OK (0.01 sec)
   
mysql> quit

Explanation

• CREATE USER 'myuser'@'localhost' IDENTIFIED BY 'xxxx'
  We use the command "create user" to create a new user called 'myuser'@'localhost', who can login to the server locally from the same machine (but not remotely from another machine), with password "xxxx".
• GRANT ALL ON *.* TO 'myuser'@'localhost'
  The newly created user has NO privilege to perform any database operation including select. We use the "grant" command to grant "all" the privileges (including select, insert, delete, and so on) to this new user on ALL the databases and ALL the tables ("on *.*"). This new user, in practice, has the same privilege as root, except that it cannot issue grantcommand. For production, you should grant only the necessary privileges on selected databases and selected tables, e.g., "grant select, insert, update on studentdb.*" - it can issue select, insert and update (but no delete, create/drop table) on ALL the tables of the database studentdb only.

3.7  Step 7: Create a new Database, a new Table in the Database, Insert Records, Query and Update

Recall that the MySQL server organizes data in the following hierarchy:

1. A system contains many databases.
2. A database contains many tables.
3. A table contains rows (records) and columns (fields).

Let's create a database called "studentdb", and a table called "class101" in the database. The table shall have three columns: id (of the type INT - integer), name (of the type VARCHAR(50) - variable-length string of up to 50 characters), gpa (of the type FLOAT - floating-point number).

CAUTION: Programmers don't use blank and special characters in NAMES (database names, table names, column names). It is either not supported, or will pose you many more challenges.

Tips on Client's Session

Before we proceed, here are some tips on using the client:

• You need to terminate your command with a semicolon (;), which sends the command to the server for processing. E.g.,

  mysql> select * from class101;
  -- Terminate a command with ';' to send the command to the server for processing

• A command can span several lines. The prompt for subsequent lines changes to -> to denote continuation. You need to terminate the command with a semicolon (;). E.g.,

  mysql> select * 
      -> from class101
      -> 
      -> ;
  -- A command can span several lines, ended with a semicolon.

  In other words, if you forget to type ';', you can type the ';' on the next line.
• You can use \c to cancel (abort) the current command. E.g.,

  mysql> select * from class101 \c
  -- abort (cancel) the command

• If you open a single/double quote, without closing it, the continuation prompt changes to '> or "> (instead of ->). For example,

  mysql> select 'xxx
      '> '        // close the single-quote
      -> \c       // abort
      
  mysql> select "xxx
      "> '        // close the single-quote
      -> \c       // abort

• You can also press Ctrl-C to abort the current command.
• You can use up/down arrow keys to retrieve the previous/next commands, from the "command history".
• (For Windows 10) You should enable Copy/Paste functions of CMD shell. To enable Copy/Paste, click the CMD's icon ⇒ Properties ⇒ Options ⇒ Edit Options ⇒ Check "Enable Ctrl key shortcuts". You can then use Ctrl-C/Ctrl-V for Copy/Paste.

SQL Programming

Let's start a client with our newly-created user "myuser".

-- Start a client
mysql -u myuser -p     // Windows
./mysql -u myuser -p   // Mac OS X
   
-- Create a new database called 'studentdb'
mysql> create database if not exists studentdb;
Query OK, 1 row affected (0.08 sec)
   
-- List all the databases in this server
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| ......             |
| studentdb          |
| ......             |
+--------------------+
x rows in set (0.07 sec)
   
-- Use 'studentdb' database as the default (current) database
-- You can refer to tables in the default database by the 'tablename' alone,
--   instead of 'databasename.tablename' for non-default database.
mysql> use studentdb;
Database changed
   
-- Remove the table 'class101' in the default database if it exists
mysql> drop table if exists class101;
Query OK, 0 rows affected, 1 warning (0.15 sec)
   
-- Create a new table called 'class101' in the default database 'studentdb',
--   with 3 columns of the specified types
mysql> create table class101 (id int, name varchar(50), gpa float);
Query OK, 0 rows affected (0.15 sec)
   
-- List all the tables in the default database 'studentdb'
mysql> show tables;
+---------------------+
| Tables_in_studentdb |
+---------------------+
| class101            |
+---------------------+
1 row in set (0.00 sec)
   
-- Describe the 'class101' table (List its columns' definition)
mysql> describe class101;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(50) | YES  |     | NULL    |       |
| gpa   | float       | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.04 sec)
   
-- Insert a row into 'class101' table.
-- Strings are single-quoted. No quotes for INT and FLOAT values.
mysql> insert into class101 values (11, 'Tan Ah Teck', 4.8);
Query OK, 1 row affected (0.03 sec)
   
-- Insert another row
mysql> insert into class101 values (22, 'Mohamed Ali', 4.9);
Query OK, 1 row affected (0.03 sec)
   
-- Select all columns (*) from table 'class101', and all rows
mysql> select * from class101;
+----+-------------+------+
| id | name        | gpa  |
+----+-------------+------+
| 11 | Tan Ah Teck |  4.8 |
| 22 | Mohamed Ali |  4.9 |
+----+-------------+------+
2 rows in set (0.00 sec)
  
-- Select some columns from table 'class101', and rows that match the conditions
mysql> select name, gpa from class101 where gpa > 4.85;
+-------------+------+
| name        | gpa  |
+-------------+------+
| Mohamed Ali |  4.9 |
+-------------+------+
1 rows in set (0.00 sec)
  
-- Update the given field of the selected records
mysql> update class101 set gpa = 4.4 where name = 'Tan Ah Teck';
Query OK, 1 row affected (0.05 sec)
Rows matched: 1  Changed: 1  Warnings: 0   
 
mysql> select * from class101;
+----+-------------+------+
| id | name        | gpa  |
+----+-------------+------+
| 11 | Tan Ah Teck |  4.4 |
| 22 | Mohamed Ali |  4.9 |
+----+-------------+------+
2 rows in set (0.00 sec)
 
-- Delete selected records
mysql> delete from class101 where id = 22;
Query OK, 1 row affected (0.03 sec)
   
mysql> select * from class101;
+----+-------------+------+
| id | name        | gpa  |
+----+-------------+------+
| 11 | Tan Ah Teck |  4.4 |
+----+-------------+------+
1 rows in set (0.00 sec)
 
-- You can STORE a set of SQL commands in a FILE (called SQL script) and run the script,
--   instead entering the commands one-by-one.
-- Use a programming text editor to CREATE a NEW FILE called "mycommands.sql" 
--   containing the following three SQL statements.
-- (For Windows) Save the file under "c:\myWebProject".
-- (For Mac OS X) Save the file under "~/myWebProject", where "~" denotes your home directory.
insert into class101 values (33, 'Kumar', 4.8);
insert into class101 values (44, 'Kevin', 4.6);
Select * from class101;

-- After you created the file, you can use the following "source" command 
--   to run the SQL script.
-- You need to provide the full path to the script.
-- (For Windows) The full-path filename is c:\myWebProject\mycommands.sql
-- (For Mac OS X) The full-path filename is ~/myWebProject/mycommands.sql
mysql> source c:\myWebProject\mycommands.sql   // For Windows
mysql> source ~/myWebProject/mycommands.sql    // For Mac OS X
Query OK, 1 row affected (0.00 sec)   -- INSERT command output
Query OK, 1 row affected (0.00 sec)   -- INSERT command output
+------+-------------+------+         -- SELECT command output
| id   | name        | gpa  |
+------+-------------+------+
|   11 | Tan Ah Teck |  4.4 |
|   33 | Kumar       |  4.8 |
|   44 | Kevin       |  4.6 |
+------+-------------+------+
3 rows in set (0.00 sec)

Exercises:

1. Select records with names starting with letter 'K'. (Hints: name like 'K%', see Section "SQL by Examples")
2. Select records with names NOT starting with letter 'K'. (Hints: name NOT like ...)
3. Select records with gpa between 4.35 and 4.65. (Hints: test-1 AND test-2)
4. Select records with names having a letter 'e'. (Hints: name like '%e%')
5. Select records with names having a letter 'e' or 'a'. (Hints: test-1 OR test-2)
6. Select records with names having a letter 'e' and gpa ≥ 4.5.

(Skip Unless... ) Read "How to Debug".

3.8  More Exercises

1. Show all the databases.
2. Create a new database called "ABCTrading".
3. Set the "ABCTrading" database as the default database.
4. Show all the tables in the default database.
5. Create a new table called "products" with the columns and type indicated below.

   +-------+----------+-------------+----------+---------+
   | id    | category | name        | quantity | price   |
   | (INT) | CHAR(3)  | VARCHAR(20) | (INT)    | (FLOAT) |
   +-------+----------+-------------+----------+---------+
   | 1001  | PEN      | Pen Red     |     5000 |  1.23   |
   | 1002  | PEN      | Pen Blue    |     8000 |  1.25   |
   | 1003  | PEN      | Pen Black   |     2000 |  1.25   |
   | 1004  | PCL      | Pencil 2B   |    10000 |  0.49   |
   | 1005  | PCL      | Pencil 2H   |     9000 |  0.48   |
   +-------+----------+-------------+----------+---------+

6. Show the table description.
7. Insert the above records and list all the records.
8. List records with name containing "Pencil".
9. List records with price ≥ 1.0.
10. Increase the price of all items by 10%, and list all the records.
11. Remove "Pen Red" from the table, and list all the records.

4.  Many-to-many Relationship

In a bookstore, a book is written by one or more authors; an author may write zero or more books. This is known as a many-to-many relationship. It is IMPOSSIBLE to capture many-to-many relationship in a SINGLE table (or one spreadsheet) with a fixed number of columns, without duplicating any piece of information! For example, if you organize the data in the table below, you will not know how many author columns to be used; and you need to repeat all the data for repeating authors.

The many-to-many relationship between books and authors can be modeled with 3 tables, as shown below. A books table contains data about books (such as title and price); an authors table contains data about the authors (such as name and email). A table called books_authors joins the books and authors tables and captures the many-to-many relationship between books and authors.

Exercises

1. Create a database called "mybookstore".
2. Use "mybookstore" as the default database.
3. Create 3 tables "books", "authors", and "books_authors" in the database "mybookstore", with column names and types as shown in the database diagram.
4. Insert the respective records into the tables, and list the contents of each of the tables.
5. Try this query and explain the output:

   SELECT books.title, books.price, authors.name
      FROM books, books_authors, authors
      WHERE books.isbn = books_authors.isbn
         AND authors.authorID = books_authors.authorID
         AND authors.name = 'Tan Ah Teck';

6. List all the books (title, price, qty) by "Tan Ah Teck" with price less than 20.
7. List all the authors (name and email) for the book title "Java for Dummies".
8. List all the books (title, price, qty) and all the authors (name and email) for books with title beginning with "Java" (Hints: title LIKE 'Java%').

5.  (Optional) Backup and Restore Databases

5.1  Backup via "mysqldump" Utility Program

You can use the "mysqldump" utility program to back up (i) the entire server (all databases), (ii) selected databases, or (ii) selected tables of a database. The "mysqldump" program generates a SQL script that can later be executed to re-create the databases, tables and their rows.

For example, the following command backups the entire "studentdb" database to a SQL script called "backup_studentdb.sql".

For Windows

-- Start a NEW "cmd"
c:
cd \myWebProject\mysql\bin
mysqldump -u myuser -p --databases studentdb > "c:\myWebProject\backup_studentdb.sql"

For Mac OS X

-- Start a NEW "terminal"
cd /usr/local/mysql/bin
./mysqldump -u myuser -p --databases studentdb > ~/myWebProject/backup_studentdb.sql
     // ~ denotes the home directory of the current login user

Study the output file, which contains CREATE DATABASE, CREATE TABLE and INSERT statements to re-create the database and tables dumped earlier.

5.2  Restore via "source" command in a mysql client

You can restore from the backup by running the "source" command in a MySQL client. For example, to restore the studentdb backup earlier:

For Windows

-- Start a MySQL client
c:
cd \myWebProject\mysql\bin
mysql -u myuser -p
-- Run the backup script to recreate the database
mysql> drop database if exists studentdb;
mysql> source c:\myWebProject\backup_studentdb.sql

For Mac OS X

-- Start a MySQL client
cd /usr/local/mysql/bin
./mysql -u myuser -p
-- Run the backup script to recreate the database
mysql> drop database if exists studentdb;
mysql> source ~/myWebProject/backup_studentdb.sql

6.  Summary of Frequently-Used Commands

(For Windows) Starting MySQL Server and Client

-- Start the Server
cd path-to-mysql-bin
mysqld --console
 
-- Shutdown the Server
Ctrl-c
 
-- Start a Client
cd path-to-mysql-bin
mysql -u username -p

(For Mac OS X) Starting MySQL Server and Client

-- Start/shutdown the Server: 
-- Use Graphical Control
 
-- Start a Client
cd /usr/local/mysql/bin
./mysql -u username -p

Frequently-used MySQL Commands

MySQL commands are NOT case sensitive.

-- General
;           -- Sends command to server for processing (or \g)
\c          -- Cancels (aborts) the current command
 
-- Database-level
DROP DATABASE databaseName;                 -- Deletes the database
DROP DATABASE IF EXISTS databaseName;       -- Deletes only if it exists
CREATE DATABASE databaseName;               -- Creates a new database
CREATE DATABASE IF NOT EXISTS databaseName; -- Creates only if it does not exists
SHOW DATABASES;                             -- Shows all databases in this server
   
-- Set default database.
-- Otherwise you need to use the fully-qualified name, in the form 
--   of "databaseName.tableName", to refer to a table.
USE databaseName
   
-- Table-level
DROP TABLE tableName;
DROP TABLE IF EXISTS tableName;
CREATE TABLE tableName (column1Definition, column2Definition, ...);
CREATE TABLE IF NOT EXISTS tableName (column1Definition, column2Definition, ...);
SHOW TABLES;              -- Shows all the tables in the default database
DESCRIBE tableName;       -- Describes the columns for the table
DESC tableName;           -- Same as above
   
-- Record-level (CURD - create, update, read, delete)
INSERT INTO tableName VALUES (column1Value, column2Value,...);
INSERT INTO tableName (column1Name, ..., columnNName) 
   VALUES (column1Value, ..., columnNValue);
DELETE FROM tableName WHERE criteria;
UPDATE tableName SET columnName = expression WHERE criteria;
SELECT column1Name, column2Name, ... FROM tableName 
   WHERE criteria
   ORDER BY columnAName ASC|DESC, columnBName ASC|DESC, ...;
  
-- Running a script of MySQL statements
SOURCE full-Path-Filename

7.  (Skip Unless...) How to Debug?

"Everything that can possibly go wrong will go wrong." The most important thing to do is to find the ERROR MESSAGES!!!

7.1  Cannot Start the MySQL Server after Installation

First of all, check if you have already started an instance of MySQL Server:

• For Windows, start the "Task Manager", select "Processes" and look for "mysqld" processes. "End" all the "mysqld" processes.
• For Mac, start the "Activity Monitor", select "All Processes" and look for "mysqld" processes. "Kill" all the "mysqld" processes.
• For Ubuntu, start the "System Monitor" and look for "mysqld" processes. "Kill" all the "mysqld" processes.

SYMPTOM: Cannot start mysql server
ERROR MESSAGES:
xxxxxx [InnoDB] The innodb_system data file 'ibdata1' must be writable
xxxxxx [InnoDB] The innodb_system data file 'ibdata1' must be writable
xxxxxx [Server] Failed to initialize DD Storage Engine
xxxxxx [Server] Data Dictionary initialization failed.
xxxxxx [Server] Aborting
PROBABLE CAUSES: An MySQL server has already started holding on to the databases
POSSIBLE SOLUTIONS: Shutdown or Kill the current server, before starting a new one.

7.2  Cannot Start the "mysql" Client

SYMPTOM: Cannot start mysql client
ERROR MESSAGE: error 2003 (HY000): Can't connect to MySQL server on 'localhost' (10061)
PROBABLE CAUSES: 
  1. MySQL Server is NOT started, or
  2. The client was connecting to the wrong port number
POSSIBLE SOLUTIONS: 
  1. Check to make sure that the MySQL server has been started. 
     Note down the server's port number from the server's console.
  2. Run a client with command "mysql -u root --port=xxxx" to specify the server's port number manually.
  3. Check "my.ini", make sure that you have a [client] section with port=xxxx.

SYMPTOM: Cannot start mysql client
ERROR MESSAGE: error 2005 (hy000) unknown mysql server host 'localhost'
PROBABLE CAUSES: Somehow your localhost is not bound to 127.0.0.1
POSSIBLE SOLUTIONS:
  1. Try "ping localhost" to check if "localhost" exists.
  2. (Windows) Check "C:\Windows\System32\drivers\etc\hosts" file. There should be an entry:
     127.0.0.1       localhost
     Remove all the other localhost entries, if any.

7.3  Error Using the "mysql" Client

ERROR MESSAGE: Stuck at entering SQL commands
PROBABLE CAUSES: Syntax errors in the current command
POSSIBLE SOLUTIONS:
  1) Abort the current command pressing Ctrl-C
  2) Abort the current command using \c
     a) Enter \c if the prompt is -> or mysql>
     b) Enter '\c if the prompt is '>
     c) Enter "\c if the prompt is ">

ERROR MESSAGE: error 1046 (3D000): No database selected
PROBABLE CAUSES: The default database is not set
POSSIBLE SOLUTIONS: 
  1) Issue command "use database" to set the default database, or
  2) Use the fully-qualified name in the form of "databaseName.tableName".
  
ERROR MESSAGE: error 1005 (HY000): Can't create table '...' (errno: 150)
PROBABLE CAUSES:
A foreign key references a parent table's column which is not indexed. Create index for that column in the parent table.

SYMPTOM: Logical error in comparing floating point numbers for equality. 
   For example, "SELECT * FROM class101 WHERE gpa = 4.4" 
   yields empty set although there is a record with gpa=4.4.
PROBABLE CAUSES: 
   "gpa" has the type of FLOAT.
   Floating point numbers are not stored "accurately".
POSSIBLE SOLUTION: 
   Do not compare two floating point number for equality. 
   Instead, specify a range, e.g., "gpa > 3.9 AND gpa < 4.1"

Link to MySQL References & Resources