Knowledge in SQL CHECK Constraint
SQL CHECK Constraint
SQL CHECK Constraint 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. ________________________________________ SQL CHECK on CREATE TABLE The following SQL creates a CHECK constraint on the "Age" column when the "Persons" table is created. The CHECK constraint ensures that you can not have any person below 18 years: MySQL: CREATE TABLE Persons ( ID int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Age int, CHECK (Age>=18) ); SQL Server / Oracle / MS Access:
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SQL DEFAULT Constraint
SQL DEFAULT Constraint The DEFAULT constraint is used to provide a default value for a column. The default value will be added to all new records IF no other value is specified. SQL DEFAULT on CREATE TABLE The following SQL sets a DEFAULT value for the "City" column when the "Persons" table is created: