Drupal's database api provides abstraction using PDO to provide support for multiple types of database servers, and allow for secure query assembly.
Here are a few examples from Eugene Ilyin's Database Queries in Drupal 8:
<?php
// Get single value:
$query = \Drupal::database()->select('node_field_data', 'nfd');
$query->addField('nfd', 'nid');
$query->condition('nfd.title', 'Potato');
$query->range(0, 1);
$nid = $query->execute()->fetchField();
// Get single row:
$query = \Drupal::database()->select('node_field_data', 'nfd');
$query->fields('nfd', ['nid', 'title']);
$query->condition('nfd.type', 'vegetable');
$query->range(0, 1);
$vegetable = $query->execute()->fetchAssoc();
// Using db like:
$query = \Drupal::database()->select('node_field_data', 'nfd');
$query->fields('nfd', ['nid', 'title']);
$query->condition('nfd.type', 'vegetable');
$query->condition('nfd.title', $query->escapeLike('ca') . '%', 'LIKE');
$vegetable = $query->execute()->fetchAllKeyed();
// Get several rows with JOIN:
$query = \Drupal::database()->select('node_field_data', 'nfd');
$query->fields('nfd', ['nid', 'title']);
$query->addField('ufd', 'name');
$query->join('users_field_data', 'ufd', 'ufd.uid = nfd.uid');
$query->condition('nfd.type', 'vegetable');
$vegetable = $query->execute()->fetchAllAssoc('nid');
// Insert row into database.
$query = \Drupal::database()->insert('flood');
$query->fields([
'event',
'identifier'
]);
$query->values([
'My event',
'My indentifier'
]);
$query->execute();
// Update row in database.
$query = \Drupal::database()->update('flood');
$query->fields([
'identifier' => 'My new identifier'
]);
$query->condition('event', 'My event');
$query->execute();
// Upsert (Update or insert if not exists)
$query = \Drupal::database()->upsert('flood');
$query->fields([
'fid',
'identifier',
]);
$query->values([
1,
'My indentifier for upsert'
]);
$query->key('fid');
$query->execute();
// Delete
$query = \Drupal::database()->delete('flood');
$query->condition('event', 'My event');
$query->execute();
?>- eilyin.name: Database Queries in Drupal 8
- [Database API D8] (https://www.drupal.org/docs/8/api/database-api)