CHECK Constraint in SQL - sql - sql tutorial - learn sql

• The CHECK constraint is used to limit the value range that can be placed in a column.
• If you define a CHECK constraint on a single column it allows only certain values for this column.
• If you define a CHECK constraint on a table it can limit the values in certain columns based on values in other columns in the row.
• The CHECK constraint ensures that all values in a column satisfy certain conditions.
• The database will only insert a new row or update an existing row if the new value satisfies the CHECK constraint.
• The CHECK constraint is used to ensure data quality.
• For example, in the following CREATE TABLE statement,

CREATE TABLE Student 
(SID integer CHECK (SID > 0), 
Last_Name varchar (30),  
First_Name varchar(30));

• Column "SID" has a constraint - its value must only include integers greater than 0. So, attempting to execute the following statement,

INSERT INTO Student VALUES (-3, 'wikitechy', 'Tutorials');

• will result in an error because the values for SID must be greater than 0.
• Please note that the CHECK constraint does not get enforced by MySQL at this time.

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