SQLite - CHECK Constraint

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The CHECK Constraint enables a condition to check the value being entered into a record. If the condition evaluates to false, the record violates the constraint and isn't entered into the table.

Example:

For example, the following SQL creates a new table called CUSTOMERS and adds five columns. Here, we add a CHECK with AGE column, so that you can not have any CUSTOMER below 18 years:

CREATE TABLE COMPANY(
   ID   INT       PRIMARY KEY     ,
   NAME          TEXT     NOT NULL,
   AGE  INT              NOT NULL UNIQUE,
   ADDRESS  CHAR (25) ,
   SALARY   REAL  ,       
   
);

If COMPANY table has already been created, then to add a CHECK constraint to AGE column, you would write a statement similar to the following:

ALTER TABLE COMPANY
   MODIFY AGE INT NOT NULL CHECK (AGE >= 18 );

You can also use following syntax, which supports naming the constraint and multiple columns as well:

ALTER TABLE COMPANY
   ADD CONSTRAINT myCheckConstraint CHECK(AGE >= 18);

DROP a CHECK Constraint:



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