Tuesday, 6 March 2018

MySQL Command Line Cheatsheet



Access monitor: mysql -u [username] -p; (will prompt for password)
Show all databases: show databases;
Access database: mysql -u [username] -p [database] (will prompt for password)
Create new database: create database [database];
Select database: use [database];
Determine what database is in use: select database();
Show all tables: show tables;
Show table structure: describe [table];
List all indexes on a table: show index from [table];
Create new table with columns: CREATE TABLE [table] ([column] VARCHAR(120), [another-column] DATETIME);
Adding a column: ALTER TABLE [table] ADD COLUMN [column] VARCHAR(120);
Adding a column with an unique, auto-incrementing ID: ALTER TABLE [table] ADD COLUMN [column] int NOT NULL AUTO_INCREMENT PRIMARY KEY;
Inserting a record: INSERT INTO [table] ([column], [column]) VALUES ('[value]', [value]');
MySQL function for datetime input: NOW()
Selecting records: SELECT * FROM [table];
Explain records: EXPLAIN SELECT * FROM [table];
Selecting parts of records: SELECT [column], [another-column] FROM [table];
Counting records: SELECT COUNT([column]) FROM [table];
Counting and selecting grouped records: SELECT *, (SELECT COUNT([column]) FROM [table]) AS count FROM [table] GROUP BY [column];
Selecting specific records: SELECT * FROM [table] WHERE [column] = [value]; (Selectors: <>!=; combine multiple selectors with ANDOR)
Select records containing [value]SELECT * FROM [table] WHERE [column] LIKE '%[value]%';
Select records starting with [value]SELECT * FROM [table] WHERE [column] LIKE '[value]%';
Select records starting with val and ending with ueSELECT * FROM [table] WHERE [column] LIKE '[val_ue]';
Select a range: SELECT * FROM [table] WHERE [column] BETWEEN [value1] and [value2];
Select with custom order and only limit: SELECT * FROM [table] WHERE [column] ORDER BY [column] ASC LIMIT [value];(Order: DESCASC)
Updating records: UPDATE [table] SET [column] = '[updated-value]' WHERE [column] = [value];
Deleting records: DELETE FROM [table] WHERE [column] = [value];
Delete all records from a table (without dropping the table itself): DELETE FROM [table]; (This also resets the incrementing counter for auto generated columns like an id column.)
Delete all records in a table: truncate table [table];
Removing table columns: ALTER TABLE [table] DROP COLUMN [column];
Deleting tables: DROP TABLE [table];
Deleting databases: DROP DATABASE [database];
Custom column output names: SELECT [column] AS [custom-column] FROM [table];
Export a database dump (more info here): mysqldump -u [username] -p [database] > db_backup.sql
Use --lock-tables=false option for locked tables (more info here).
Import a database dump (more info here): mysql -u [username] -p -h localhost [database] < db_backup.sql
Logout: exit;

Aggregate functions

Select but without duplicates: SELECT distinct name, email, acception FROM owners WHERE acception = 1 AND date >= 2015-01-01 00:00:00
Calculate total number of records: SELECT SUM([column]) FROM [table];
Count total number of [column] and group by [category-column]SELECT [category-column], SUM([column]) FROM [table] GROUP BY [category-column];
Get largest value in [column]SELECT MAX([column]) FROM [table];
Get smallest value: SELECT MIN([column]) FROM [table];
Get average value: SELECT AVG([column]) FROM [table];
Get rounded average value and group by [category-column]SELECT [category-column], ROUND(AVG([column]), 2) FROM [table] GROUP BY [category-column];

Multiple tables

Select from multiple tables: SELECT [table1].[column], [table1].[another-column], [table2].[column] FROM [table1], [table2];
Combine rows from different tables: SELECT * FROM [table1] INNER JOIN [table2] ON [table1].[column] = [table2].[column];
Combine rows from different tables but do not require the join condition: SELECT * FROM [table1] LEFT OUTER JOIN [table2] ON [table1].[column] = [table2].[column]; (The left table is the first table that appears in the statement.)
Rename column or table using an aliasSELECT [table1].[column] AS '[value]', [table2].[column] AS '[value]' FROM [table1], [table2];

Users functions

List all users: SELECT User,Host FROM mysql.user;
Create new user: CREATE USER 'username'@'localhost' IDENTIFIED BY 'password';
Grant ALL access to user for * tables: GRANT ALL ON database.* TO 'user'@'localhost';

Find out the IP Address of the Mysql Host

SHOW VARIABLES WHERE Variable_name = 'hostname';



Other ref: https://www.geeksforgeeks.org/sql-tutorial/

Example

The following code block is an example, which creates a CUSTOMERS table with an ID as a primary key and NOT NULL are the constraints showing that these fields cannot be NULL while creating records in this table −
SQL> CREATE TABLE CUSTOMERS(
   ID   INT              NOT NULL,
   NAME VARCHAR (20)     NOT NULL,
   AGE  INT              NOT NULL,
   ADDRESS  CHAR (25) ,
   SALARY   DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);
You can verify if your table has been created successfully by looking at the message displayed by the SQL server, otherwise you can use the DESCcommand as follows −
SQL> DESC CUSTOMERS;
+---------+---------------+------+-----+---------+-------+
| Field   | Type          | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ID      | int(11)       | NO   | PRI |         |       |
| NAME    | varchar(20)   | NO   |     |         |       |
| AGE     | int(11)       | NO   |     |         |       |
| ADDRESS | char(25)      | YES  |     | NULL    |       |
| SALARY  | decimal(18,2) | YES  |     | NULL    |       |
+---------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
Now, you have CUSTOMERS table available in your database which you can use to store the required information related to customers.

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