Handle database schemas on Drupal 8

Get Database Schema

$schema = \Drupal\Core\Database\Database::getConnection()->schema();

Create a table.

$spec = array(

'description' => 'New table description',

'fields' => array(

  'id' => array(

    'type' => 'serial',

    'not null' => TRUE,

  ),

  'name' => array(

    'type' => 'varchar',

    'length' => 64,

    'not null' => TRUE,

    'default' => '',

  ),

  'value' => array(

    'type' => 'varchar',

    'length' => 64,

    'not null' => TRUE,

    'default' => '',

  ),

),

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

);

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

 

 

Drop / Delete a field.

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

$schema->dropField('the_table_name', 'field_to_drop');

Add a field to a table.

$spec = array(

    'type' => 'varchar',

    'length' => '255',

    'not null' => TRUE,

    'default' => '0',

);

$schema->addField('the_table_name', 'field_to_add', $spec);

Examples

Delete a table field from hook_update_N()

/**

 * Update 8001, Delete Field 'field_to_delete' from table 'the_test_table'.

 */

function mymodule_update_8001(&$sandbox) {

    $schema = \Drupal\Core\Database\Database::getConnection()->schema();

    $schema->dropField('the_test_table', 'field_to_delete');

    return ('The field field_to_delete has been dropped from the_test_table');

}

More : https://api.drupal.org/api/drupal/includes!database!schema.inc/group/schemaapi/7.x