Mysql self-increment and uniqueness constraint

When a data table has been deleted many times, its self-increment column will be very chaotic and unattractive, so we need to reorder it so that it starts from 1 again.

How to do this: delete the original id field in the data table, and then re-establish the id field

Delete the id field:

Alter table bumen drop id

Rebuild Field:

ALTER TABLE bumen ADD id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY FIRST

-- INT UNSIGNED unsigned integers (pure numbers). FIRST is inserted at the beginning of the table and at the end of the table by default.

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Custom value-added

The value-added setting starts from 50:

Create table bumen (id int not null primary key auto_increment) auto_increment=50,charset=gbk;-specifies that the language name should be placed outside the parentheses of the field

The modification starts with the increment of 100:

ALTER TABLE bumen AUTO_INCREMENT = 100;-- change the table after it is created

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Create a department table with three fields: id serial number, department name, and manager:

CREATE TABLE bu5 (

Id INT (5) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY

NAME CHAR (10) NOT NULL UNIQUE

Manger VARCHAR (20) NOT NULL) charset=gbk

-- id pure digit 5-digit, non-null, self-growing, primary key; name 10-bit, non-null, uniqueness constraint, manger adaptive 20-bit, non-null

Add a unique harness to the field:

ALTER TABLE bu5 CHANGENAME NAME CHAR (10) UNIQUE;-redefines the name field

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