What syntax is used to decrement fields in sql
Using the AUTO_INCREMENT keyword in SQL can realize field decrement, that is, when inserting a new record, the integer field specified as decrement will automatically increment. Notes include: Decrementing fields must be unique primary keys or unique indexes, cannot be used with DEFAULT or NOT NULL constraints, and can only be used in INSERT operations.
Syntax for field auto-decrement in SQL
In SQL, you can use AUTO_INCREMENT Keyword to implement field auto-decrement.
Syntax
<code>CREATE TABLE table_name ( id INT(11) NOT NULL AUTO_INCREMENT, ... PRIMARY KEY (id) );</code>
How to use
- Specify the field to be decremented when creating the table (usually integer type).
- Use the
AUTO_INCREMENTkeyword to mark a field as auto-incrementing. - This field will be automatically incremented when a new record is inserted.
Example
Consider the following table:
<code>CREATE TABLE products ( id INT(11) NOT NULL AUTO_INCREMENT, name VARCHAR(255) NOT NULL, PRIMARY KEY (id) );</code>
After inserting two records, the value of the "id" field will automatically increment to 1 And 2:
<code>INSERT INTO products (name) VALUES ('Product 1');
INSERT INTO products (name) VALUES ('Product 2');</code>
Notes
- The decrementing field must be the unique primary key or unique index of the table.
- Decreasing fields cannot be used with
DEFAULTorNOT NULLconstraints. - Decreasing fields can only be used in INSERT operations.
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