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This article mainly introduces the relevant knowledge of "how to automatically add mysql". The editor shows you the operation process through an actual case. The operation method is simple, fast and practical. I hope this article "how to achieve automatic increase in mysql" can help you solve the problem.

In mysql, you can add automatically using the "AUTO INCREMENT" field, which generates a unique number when a new record is inserted into the table, with a default starting value of 1, incrementing each new record by 1, and the syntax is "field name data type AUTO_INCREMENT".

The operating environment of this tutorial: windows10 system, mysql8.0.22 version, Dell G3 computer.

How to automatically add mysql

The role of automatic growth:

Problem: after setting the primary key constraint for the data table, each time you insert a record, the insert will fail if the inserted value already exists.

How to solve this: generate an automatically growing value for the primary key.

Auto-growing syntax:

Field name data type AUTO_INCREMENT

Instructions for use:

1. There can be only one auto-grow field in a table

two。 The data type of this field is an integer type

3. Must be defined as a key, such as UNIQUE KEY, PRIMARY KEY

4. If you insert NULL, 0, DEFAULT for an auto-grow field or omit the field when you insert it, the field uses the auto-grow value

5. If a specific value is inserted, the automatic growth value will not be used

6. The value of automatic growth increases from 1 to 1 at a time.

7. If the inserted value is greater than the automatically increasing value, the next inserted auto-growing value will automatically be added by 1 using the maximum value.

8. If the inserted value is less than the automatic growth value, it will not affect the automatic growth value.

9. When you delete a record using DELETE, the auto-growth value does not decrease or fill the gap.

Examples of automatic growth usage:

-- automatic growth using demo Create Table my_auto (id Int Unsigned Primary Key Auto_Increment,username Varchar (20)); # View DESC my_auto

Auto-growth usage demo:

# if the id field is omitted during insertion, the auto-increment value Insert Into my_auto (username) Values ('a') will be used; # if you insert null for the id field, the auto-increment value Insert Into my_auto Values (Null,'b') will be used; # the specific value 6Insert Into my_auto Values will be inserted for the id field (6); # insert 0 for the id field and use the auto-increment value Insert Into my_auto Values (0); # View Select * From my_auto

View automatic growth values:

# View the automatic growth value Show Create Table my_auto

Modify or delete automatic growth for existing tables:

# modify automatic growth value Alter Table my_auto Auto_Increment=10;#, delete automatic growth value Alter Table my_auto Modify id Int Unsigned;# and add automatic growth value Alter Table my_auto Modify id Int Unsigned Auto_Increment to id again

Note:

1. After automatic growth is deleted and re-added, the initial value of automatic growth is automatically set to the column's existing maximum value plus 1.

two。 When modifying the automatic growth value, if the modified value is less than the maximum value seen in the column, the modification will not take effect.

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