Alter table structure on Drupal 8

To update a table you must create a custom module. Example , Here we use mymodule.

Note : Initially you must create a database table. Example on hook_schema() of mymodule.install :

/**

 * Schema.

 */

function mymodule_schema() {

  $schema['mymodule_table1'] = [

    'description' => 'My test table',

    'fields' => [

      'id' => [

        'type' => 'serial',

        'not null' => TRUE,

      ],

      'test_field_1' => [

        'type' => 'int',

      ],

    ],

    'primary key' => ['id'],

  ];

  return $schema;

}

Update a table from module update hook

Hook : hook_update_N().

You can update tables from anyware of your module, but it is strongly recomended to use this hook.

use Drupal\Core\Database\Database;

/**

 * Update Table mymodule_table1, add a field and remove a field.

 */

mymodule_update_8001(){

  $ret = [];

  $con = Database::getConnection();

  // Remove 'test_field_1' from mymodule_table1 DB.

  $ret[] = $con->schema()->dropField('mymodule_table1', 'test_field_1');

  // Add 'test_field_2' to mymodule_table1 DB.

  $spec = [

    'type' => 'text',

    'size' => 'tiny',

  ];

  $ret[] = $con->schema()->addField('mymodule_table1', 'test_field_2', $spec);

  return $ret;

}

Create a new table

$spec = array(

'description' => 'My description',

'fields' => array(

  'myfield1' => array(

    'description' => 'Myfield1 description.',

    'type' => 'varchar',

    'length' => 255,

    'not null' => TRUE,

    'default' => '',

  ),

  'myfield2' => array(

    'description' => 'Myfield2 description',

    'type' => 'text',

    'not null' => TRUE,

  ),

),

'primary key' => array('myfield1'),

);

$schema = Database::getConnection()->schema();

$schema->createTable('mytable2', $spec);

Adding primary keys or indexes

$spec = array('myfield1');

$schema = Database::getConnection()->schema();

// A normal index.

$schema->addIndex('mytable', $spec);

// A primary key.

$schema->addPrimaryKey('mytable', $spec);

// A unique key.

$schema->addUniqueKey('mytable', $spec);