CHECK Constraint

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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

  • You can specify CHECK constraints 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 add CHECK constraints to columns that were created earlier in the same transaction. For an example, see Add the CHECK constraint.

  • You can have multiple CHECK constraints on a single column but for performance optimization you should combine them using logical operators. For example, you should specify:

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

    as:

    warranty_period INT CHECK (warranty_period BETWEEN 0 AND 24)

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

Syntax

You can define CHECK constraints at the column level, where the constraint applies only to a single column, and at the table level.

You can also add CHECK constraints to a table using ADD CONSTRAINT.

Column level

CREATE TABLE table_name ( column_name column_type CHECK ( check_expr ) column_constraints , column_table_def table_constraints ) )
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

The following example specifies the column-level CHECK constraint that a quantity_on_hand value must be greater than 0.

> 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

CREATE TABLE table_name ( column_table_def , CONSTRAINT constraint_name CHECK ( check_expr ) table_constraints )
Parameter Description
table_name The name of the table you're creating.
column_def Definitions for any other columns in the table.
constraint_name The name 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 to apply.

Example

The following example specifies the table-level CHECK constraint named ok_to_supply that a quantity_on_hand value must be greater than 0 and a warehouse_id must be between 100 and 200.

> 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

The following example demonstrates that when you specify the CHECK constraint that a quantity_on_hand value must be greater than 0, and you attempt to insert the value 0, CockroachDB returns an error.

> 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)

See also


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