SQLite NOT NULL Keyword

By default, a column of a table holds NULL values. The SQLite NOT NULL keyword which is a constraint and it is used to enforce a column to NOT accept NULL values. This ensures the column to always have a value. This implies that a new record can not be inserted without providing a value to this column. Similarly, this column can not be updated with a NULL value.

SQLite NOT NULL constraint with CREATE TABLE

The below mentioned statement creates a table called Employee which contains five columns: EmpID, Name, City, Age and Salary in which NOT NULL constraint is applied on columns EmpID, Name and City.

CREATE TABLE Employee (
  EmpID INT NOT NULL,
  Name VARCHAR(255) NOT NULL,
  City VARCHAR(100) NOT NULL,
  Age INT,
  Salary DECIMAL(18,2)
);

SQLite NOT NULL constraint with ALTER TABLE

SQLite does not support ALTER TABLE statement to add a NOT NULL constraint to the existing table. However this can be achieved using following steps:

• The foreign key constraint should be checked off
• Rename the table to some other name
• Create a new table with same structure but NOT NULL constraint added
• Copy the data from renamed table to new table
• In the end, turn on the foreign key constraints

For example, to enforce NOT NULL constraint on EmpID column of the existing table Employee, the following statement can be used:

PRAGMA foreign_keys=off;

BEGIN TRANSACTION;

ALTER TABLE Employee RENAME TO Employee_old;

CREATE TABLE Employee (
  EmpID INT NOT NULL,
  Name VARCHAR(255),
  City VARCHAR(100),
  Age INT,
  Salary DECIMAL(18,2)
);

INSERT INTO Employee SELECT * FROM Employee_old;

COMMIT;

PRAGMA foreign_keys=on;

Remove NOT NULL constraint

SQLite does not support ALTER TABLE or DROP statement to drop an existing NOT NULL constraint from a table. To achieve this, the following steps can be used:

• The foreign key constraint should be checked off
• Rename the table to some other name
• Create a new table with same structure but NOT NULL constraint dropped
• Copy the data from renamed table to new table
• In the end, turn on the foreign key constraints

For example, to drop NOT NULL constraint from EmpID column of the existing table Employee, the following statement can be used:

PRAGMA foreign_keys=off;

BEGIN TRANSACTION;

ALTER TABLE Employee RENAME TO Employee_old;

CREATE TABLE Employee (
  EmpID INT,
  Name VARCHAR(255),
  City VARCHAR(100),
  Age INT,
  Salary DECIMAL(18,2)
);

INSERT INTO Employee SELECT * FROM Employee_old;

COMMIT;

PRAGMA foreign_keys=on;