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6 install.php hook_schema()
7 system.api.php hook_schema()

Define the current version of the database schema.

A Drupal schema definition is an array structure representing one or more tables and their related keys and indexes. A schema is defined by hook_schema() which must live in your module's .install file.

By implementing hook_schema() and specifying the tables your module declares, you can easily create and drop these tables on all supported database engines. You don't have to deal with the different SQL dialects for table creation and alteration of the supported database engines.

See the Schema API Handbook at for details on schema definition structures.

Return value

A schema definition structure array. For each element of the array, the key is a table name and the value is a table structure definition.

Related topics

66 functions implement hook_schema()

2 invocations of hook_schema()


drupal/modules/system/system.api.php, line 2893
Hooks provided by Drupal core and the System module.


function hook_schema() {
  $schema['node'] = array(
    // example (partial) specification for table "node"
    'description' => 'The base table for nodes.', 
    'fields' => array(
      'nid' => array(
        'description' => 'The primary identifier for a node.', 
        'type' => 'serial', 
        'unsigned' => TRUE, 
        'not null' => TRUE,
      'vid' => array(
        'description' => 'The current {node_revision}.vid version identifier.', 
        'type' => 'int', 
        'unsigned' => TRUE, 
        'not null' => TRUE, 
        'default' => 0,
      'type' => array(
        'description' => 'The {node_type} of this node.', 
        'type' => 'varchar', 
        'length' => 32, 
        'not null' => TRUE, 
        'default' => '',
      'title' => array(
        'description' => 'The title of this node, always treated as non-markup plain text.', 
        'type' => 'varchar', 
        'length' => 255, 
        'not null' => TRUE, 
        'default' => '',
    'indexes' => array(
      'node_changed' => array('changed'), 
      'node_created' => array('created'),
    'unique keys' => array(
      'nid_vid' => array('nid', 'vid'), 
      'vid' => array('vid'),
    'foreign keys' => array(
      'node_revision' => array(
        'table' => 'node_revision', 
        'columns' => array('vid' => 'vid'),
      'node_author' => array(
        'table' => 'users', 
        'columns' => array('uid' => 'uid'),
    'primary key' => array('nid'),
  return $schema;