MySQL common statements

preparation ： Example of creating a table

CREATE TABLE `user` (
  `id` int(11) NOT NULL COMMENT ' Primary key ',
  `name` varchar(255) DEFAULT NULL COMMENT ' full name ',
  `age` int(11) DEFAULT NULL COMMENT ' Age ',
  `create_time` datetime DEFAULT NULL COMMENT ' Creation time ',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT=' User table ';

explain ： Table name ：user, Database name ：aaa.

1. mysql Query the field name of the table in the database 、 Attributes such as type and comment

1). Query statement ：

SELECT
	COLUMN_NAME,
	DATA_TYPE,
	COLUMN_COMMENT
FROM
	information_schema. COLUMNS
WHERE
	table_name = 'user'
AND table_schema = 'aaa';

2). Query results ：

2. mysql Index query and addition

1). Query the index in the table ：

SHOW INDEX FROM user

2). Add an index to a field ：

ALTER TABLE `user` ADD INDEX idx_name (`name`);

explain ：INDEX： General index .

3). Query results ：
explain ：id Primary key , When you create or set a primary key ,mysql A unique index corresponding to the primary key will be automatically added , There is no need to add any more .

3. sql And DDL Statement operation

turn ：https://blog.csdn.net/miachen520/article/details/51736333