In This Article, You Will Know About SQL CHECK Constraint.
Before moving ahead, let’s know a bit about the SQL UNIQUE Constraint.
Table of Contents
SQL CHECK Constraint
The SQL CHECK Constraint applies a rule or set of rules that check the values based on certain conditions.
Table1: Student_Info
Serial Number | Name | Class | Roll_No | Subject |
1 | A | I | 111 | Eco |
2 | B | II | 121 | Math |
3 | C | III | 131 | Sci |
4 | D | IV | 141 | Eng |
MySQL Server
Example: Use the CHECK Constraint to return the data based on a rule.
CREATE TABLE Student_Info (
Serial Number int NOT NULL,
Name char(10),
Class char(5),
Roll_No int,
CHECK (Roll_No = 121)
);
SQL Server
Example: Use the CHECK Constraint to return the data based on a rule.
CREATE TABLE Student_Info (
Serial Number int NOT NULL,
Name char(10),
Class char(5),
Roll_No int CHECK (Roll_No = 121)
);
Apply CHECK on multiple columns after the table is created.
MySQL / SQL Server
Example: Use the CHECK Constraint to return the data based on a rule.
CREATE TABLE Student_Info (
Serial Number int NOT NULL,
Name char(10),
Class char(5),
Roll_No int,
CONSTRAINT Table_Constraint CHECK (Serial Number < 4 AND Roll_No >= 121)
);
SQL CHECK on ALTER TABLE
Apply CHECK after the table is created.
MySQL / SQL Server
Example: Use the CHECK Constraint to return the data based on a rule.
ALTER TABLE Student_Info
ADD CHECK (Name = 'C');
Apply CHECK on multiple columns after the table is created.
MySQL / SQL Server
Example: Use the CHECK Constraint to return the data based on a rule.
ALTER TABLE Student_Info
ADD CONSTRAINT Table_Constraint CHECK (Serial Number < 4 AND Roll_No >= 121);
DROP CHECK Constraint
SQL Server
Example: Use the CHECK Constraint to return the data based on a rule.
ALTER TABLE Student_Info
DROP CONSTRAINT Table_Constraint;
MySQL
Example: Use the CHECK Constraint to return the data based on a rule.
ALTER TABLE Student_Info
DROP CHECK Table_Constraint;
