The best SQL UNIQUE constraint Tutorial In 2024, In this tutorial you can learn SQL UNIQUE constraint,CREATE TABLE SQL UNIQUE constraint when,SQL UNIQUE constraint ALTER TABLE when,Undo UNIQUE constraint,
UNIQUE constraint uniquely identifies each record in a database table.
UNIQUE and PRIMARY KEY constraints are column or set of columns provides a uniqueness guarantee.
PRIMARY KEY constraint automatically has a UNIQUE constraint defined.
Note that each table can have multiple UNIQUE constraints, but each table can have only one PRIMARY KEY constraint.
The following SQL when the "Persons" table is created to create a UNIQUE constraint on the "P_Id" column:
MySQL:
SQL Server / Oracle / MS Access:
To name UNIQUE constraints UNIQUE constraints and define multiple columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
When the table has been created, create a UNIQUE constraint in the column for "P_Id", please use the following SQL:
MySQL / SQL Server / Oracle / MS Access:
To name UNIQUE constraints UNIQUE constraints and define multiple columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
To drop a UNIQUE constraint, use the following SQL:
MySQL:
SQL Server / Oracle / MS Access: