TABLE_CONSTRAINTS view

The TABLE_CONSTRAINTS view contains the primary and foreign key relations in a BigQuery dataset.

In typical relational databases, primary keys and foreign keys are used to ensure data integrity. A primary key value is unique for each row and is not NULL. Each foreign key value in a row must be present in the primary key column of the primary key table, or be NULL. Primary and foreign key relationships are created and managed through DDL statements.

Limitations

  • Value constraints for primary keys and foreign keys are not enforced. Users need to ensure that values match their respective constraints, otherwise they may get incorrect results. Specifically:
    • Primary keys must have unique values.
    • Primary keys cannot exceed 16 columns.
    • Foreign keys must have values that are present in the primary key table column. These values can be NULL.
    • Primary keys and foreign keys must be of one of the following types: BIGNUMERIC, BOOLEAN, DATE, DATETIME, INT64, NUMERIC, STRING, or TIMESTAMP.
  • Primary keys and foreign keys can only be set on top-level columns.
  • The primary keys cannot be named.
  • Tables with primary key constraints cannot be renamed.
  • A table can contain up to 64 foreign keys defined in the table.
  • A foreign key cannot refer to a column in the same table.
  • Fields that are part of primary key constraints or foreign key constraints cannot be renamed, or have their type changed.
  • If you copy, clone, restore, or snapshot a table without the -a or --append_table option, the source table constraints are copied and overwritten to the destination table. If you use the -a or --append_table option, only the source table records are added to the destination table without the table constraints.

Required permissions

You need the following Identity and Access Management (IAM) permissions:

  • bigquery.tables.get for viewing primary and foreign key definitions.
  • bigquery.tables.list for viewing table information schemas.

Each of the following predefined roles has the needed permissions to perform the workflows detailed in this document:

  • roles/bigquery.dataEditor
  • roles/bigquery.dataOwner
  • roles/bigquery.admin

For more information about IAM roles and permissions in BigQuery, see Predefined roles and permissions.

Schema

The INFORMATION_SCHEMA.TABLE_CONSTRAINTS view has the following schema:

Column Name Type Meaning

CONSTRAINT_CATALOG

STRING

The constraint project name.

CONSTRAINT_SCHEMA

STRING

The constraint dataset name.

CONSTRAINT_NAME

STRING

The constraint name.

TABLE_CATALOG

STRING

The constrained table project name.

TABLE_SCHEMA

STRING

The constrained table dataset name.

TABLE_NAME

STRING

The constrained table name.

CONSTRAINT_TYPE

STRING

Either PRIMARY KEY or FOREIGN KEY.

IS_DEFERRABLE

STRING

YES or NO depending on if a constraint is deferrable. Only NO is supported.

INITIALLY_DEFERRED

STRING

Only NO is supported.

ENFORCED

STRING

YES or NO depending on if the constraint is enforced.
Only NO is supported.

Scope and syntax

Queries against this view must include a dataset qualifier. For queries with a dataset qualifier, you must have permissions for the dataset. For more information see Syntax. The following table shows the region and resource scopes for this view:

View name Resource scope Region scope
[PROJECT_ID.]DATASET.INFORMATION_SCHEMA.TABLE_CONSTRAINTS; Dataset level Dataset location
Replace the following:

  • Optional: PROJECT_ID: the ID of your Google Cloud project. If not specified, the default project is used.

    Examples

    The following query shows the constraints for a single table in a dataset:

    SELECT *
FROM PROJECT_ID.DATASET.INFORMATION_SCHEMA.TABLE_CONSTRAINTS
WHERE table_name = TABLE;

    Replace the following:

    • PROJECT_ID: Optional. The name of your cloud project. If not specified, this command uses the default project.
    • DATASET: The name of your dataset.
    • TABLE: The name of the table.

    Conversely, the following query shows the constraints for all tables in a single dataset.

    SELECT *
FROM PROJECT_ID.DATASET.INFORMATION_SCHEMA.TABLE_CONSTRAINTS;

    With existing constraints, the query results are similar to the following:

    +-----+---------------------+-------------------+-----------------------+---------------------+--------------+------------+-----------------+---------------+--------------------+----------+
| Row | constraint_catalog  | constraint_schema |    constraint_name    |    table_catalog    | table_schema | table_name | constraint_type | is_deferrable | initially_deferred | enforced |
+-----+---------------------+-------------------+-----------------------+---------------------+--------------+------------+-----------------+---------------+--------------------+----------+
|   1 | myConstraintCatalog | myDataset         | orders.pk$            | myConstraintCatalog | myDataset    | orders     | PRIMARY KEY     | NO            | NO                 | NO       |
|   2 | myConstraintCatalog | myDataset         | orders.order_customer | myConstraintCatalog | myDataset    | orders     | FOREIGN KEY     | NO            | NO                 | NO       |
+-----+---------------------+-------------------+-----------------------+---------------------+--------------+------------+-----------------+---------------+--------------------+----------+

    If the table or dataset has no constraints, the query results look like this:

    +-----------------------------+
| There is no data to display |
+-----------------------------+