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This article introduces what add constraint statements in mysql, the content is very detailed, interested friends can refer to, I hope it can be helpful to you.

-- add table comments

CREATE TABLE user (

Id int PRIMARY KEY AUTO_INCREMENT COMMENT 'primary key'

Name VARCHAR (10) COMMENT 'name'

Age TINYINT

Birth DATETIME

Salary DOUBLE (7 dint 2)

Tel char (11)

) COMMENT 'user Table'

-- add default constraint

CREATE TABLE user (

Id int PRIMARY KEY AUTO_INCREMENT COMMENT 'primary key'

Name VARCHAR (10) COMMENT 'name'

Age TINYINT

Birth DATETIME

Salary DOUBLE (7 dint 2)

Tel char (11)

) COMMENT 'user Table'

-- add unique constraints

CREATE TABLE register (

Id int PRIMARY KEY AUTO_INCREMENT

Name VARCHAR (10) UNIQUE KEY

RegisTime TIMESTAMP DEFAULT CURRENT_TIMESTAMP ()

Fund DOUBLE (9 dint 2) DEFAULT 1000000.00

Tel char (11)

)

-- non-empty constraint

CREATE TABLE register (

Id int PRIMARY KEY AUTO_INCREMENT

Name VARCHAR (10) DEFAULT NULL UNIQUE KEY

RegisTime TIMESTAMP DEFAULT CURRENT_TIMESTAMP ()

Fund DOUBLE (9 dint 2) DEFAULT 1000000.00

Tel char (11) NOT NULL

)

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