[Distinct] MySQL auto-increment Field

From: http://www.linuxidc.com/Linux/2008-08/15068.htm

1. Keywords
Auto_increment

2. Auto-increment usage
Example:
Create Table animals (ID mediumint not null auto_increment,
Name char (30) not null,
Primary Key (ID ));

3. Auto-Increment

Q: How to obtain the current maximum auto-increment value?
 

A: Select @ identity

Q: How to obtain the current auto-increment maximum value of a table?
A: Select max (ID) from table

Q: What is auto-increment?
A: Generally, you can obtain the ID of the data you just inserted by using select max (ID) from table. Last_insert_id is table-independent. If you insert data to table A and then insert data to table B, last_insert_id will change.

Insert multiple records using a single insert statement. last_insert_id returns a list.

@ Identity refers to the value of the auto-incrementing column corresponding to the last time data is inserted into a table with the identity attribute (that is, the auto-incrementing column). It is a global variable defined by the system. For example, if the auto-increment column of Table A is ID, after a row of data is inserted into Table A, if the value of the auto-increment column is automatically increased to 101 after the data is inserted, the value obtained through select @ identity is 101.

Note: last_insert_id is a function.
Usage: last_insert_id ()

Q: last_insert_id () in MySQL and @ identity in MSSQL
A: According to application requirements, you often need to obtain the id value of the records just inserted into the database table.
You can use the last_insert_id () function in MySQL and @ identity in MSSQL. A convenient function.

However, note that when inserting multiple records using the insert statement, last_insert_id () returns the first ID value, while @ identity returns the last record.

Q: mysql_insert_id () and last_insert_id ()
A: mysql_insert_id () converts the return value of MySQL's internal c api function mysql_insert_id () to long (INT in PHP ). If the column type of auto_increment is bigint, the value returned by mysql_insert_id () is incorrect. The SQL function last_insert_id () in MySQL can be used in SQL queries.

MySQL last_insert_id () Description mysql_insert_id () is implemented by calling last_insert_id.

Use last_insert_id ()... in MySQLProgramUse mysql_insert_id ().