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
CHECKconstraints at the column or table level and can reference other columns within the table. Internally, all column-levelCHECKconstraints are converted to table-level constraints so they can be handled consistently.You can add
CHECKconstraints to columns that were created earlier in the same transaction. For an example, see Add theCHECKconstraint.You can have multiple
CHECKconstraints 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
CHECKconstraint, theCHECKconstraint 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
| 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
| 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)
