CHECK Constraint

On this page

The CHECK constraint specifies that values for the column in INSERT or UPDATE statements must return TRUE or NULL for a Boolean expression. If any values return FALSE, the entire statement is rejected.

Details

If you add a CHECK constraint to an existing table, added values, along with any updates to current values, are checked. To check the existing rows, use VALIDATE CONSTRAINT.
CHECK constraints may be specified at the column or table level and can reference other columns within the table. Internally, all column-level CHECK constraints are converted to table-level constraints so they can be handled consistently.
You can have multiple CHECK constraints on a single column but ideally, for performance optimization, these should be combined using the logical operators. For example:

  warranty_period INT CHECK (warranty_period >= 0) CHECK (warranty_period <= 24)

should be specified as:

  warranty_period INT CHECK (warranty_period BETWEEN 0 AND 24)

When a column with a CHECK constraint is dropped, the CHECK constraint is also dropped.

Syntax

CHECK constraints can be defined at the table level. However, if you only want the constraint to apply to a single column, it can be applied at the column level.

Note:

You can also add the CHECK constraint to existing tables through ADD CONSTRAINT.

Column level

Parameter	Description
`table_name`	The name of the table you're creating.
`column_name`	The name of the constrained column.
`column_type`	The constrained column's data type.
`check_expr`	An expression that returns a Boolean value; if the expression evaluates to `FALSE`, the value cannot be inserted.
`column_constraints`	Any other column-level constraints you want to apply to this column.
`column_def`	Definitions for any other columns in the table.
`table_constraints`	Any table-level constraints you want to apply.

Example

> CREATE TABLE inventories (
    product_id        INT NOT NULL,
    warehouse_id      INT NOT NULL,
    quantity_on_hand  INT NOT NULL CHECK (quantity_on_hand > 0),
    PRIMARY KEY (product_id, warehouse_id)
  );

Table level

Parameter	Description
`table_name`	The name of the table you're creating.
`column_def`	Definitions for any other columns in the table.
`name`	The name you want to use for the constraint, which must be unique to its table and follow these identifier rules.
`check_expr`	An expression that returns a Boolean value; if the expression evaluates to `FALSE`, the value cannot be inserted.
`table_constraints`	Any other table-level constraints you want to apply.

Example

> CREATE TABLE inventories (
    product_id        INT NOT NULL,
    warehouse_id      INT NOT NULL,
    quantity_on_hand  INT NOT NULL,
    PRIMARY KEY (product_id, warehouse_id),
    CONSTRAINT ok_to_supply CHECK (quantity_on_hand > 0 AND warehouse_id BETWEEN 100 AND 200)
  );

Usage example

CHECK constraints may be specified at the column or table level and can reference other columns within the table. Internally, all column-level CHECK constraints are converted to table-level constraints so they can be handled in a consistent fashion.

> CREATE TABLE inventories (
    product_id        INT NOT NULL,
    warehouse_id      INT NOT NULL,
    quantity_on_hand  INT NOT NULL CHECK (quantity_on_hand > 0),
    PRIMARY KEY (product_id, warehouse_id)
  );

> INSERT INTO inventories (product_id, warehouse_id, quantity_on_hand) VALUES (1, 2, 0);

pq: failed to satisfy CHECK constraint (quantity_on_hand > 0)

Pricing

Contact us

Sign In