what are the constraints in sql
NOT NULL # Ensures a column cannot have a NULL value
UNIQUE # Ensures all values in a column are unique
PRIMARY KEY # Identifies a record in a table, is NOT NULL & UNIQUE
FOREIGN KEY # References a unique record from another table
CHECK # Ensures all column values satisfy a condition
DEFAULT # Set a default value for a column if none is entered
INDEX # Quick way of retrieving records from databasecheck constraint in sql
CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
City varchar(255),
CONSTRAINT CHK_Person CHECK (Age>=18 AND City='Sandnes')
);check constraint in sql
#For one column
CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int CHECK (Age>=18)
);Copyright © 2021 Codeinu
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