MySQL - autoincrement constraint of table fields

Set the table field value to increase automatically （AUTO_INCREMENT）

AUTO_INCREMENT yes MySQL The only extended integrity constraint , When inserting a new record into a database table , The value on the field automatically generates a unique ID. In specific settings AUTO_INCREMENT When restrained , Only one field in a database table can use this constraint , The data type of this field must be integer .
Because of the settings AUTO_INCREMENT The constrained field will generate a unique ID, Therefore, this field is often set to PK Primary key .
It is very simple to set the automatic increase constraint of a field value in the table , Can be in MySQL Database management system through SQL sentence AUTO_INCREMENT To achieve , Its grammatical form is as follows ：

CREATE TABLE tablename(
    propName propType AUTO_INCREMENT, ......
);

In the above statement ,tablename The parameter indicates the field name of the non empty constraint to be set ,propName The parameter name is ,propType Attribute type ,propName Fields should be set to automatically add constraints . By default , Field propName From 1 Began to increase , Every time you add a record , The value of this field in the record will be in the previous record ( Or the existing maximum （ Including what once existed ）) On the basis of 1.

mysql> create table class4(id int primary key AUTO_INCREMENT, name varchar(64), teacher varchar(64));	# Create table class4, Set up id List as primary key / Self growth 
mysql> desc class4;		# Query table class4 Constraint information 

Be careful : mysql8 in ,AUTO_INCREMENT Must be set as key ( Primary key 、 Both foreign and unique keys )！ Otherwise, an error will be reported ！