[Drupal-8] How to Handle Select, Update, Delete Database Operations in Drupal 8?

In Drupal 8, the usage of database operations such as select, update and delete are slightly changed from Drupal 7. The db_query() is deprecated in Drupal 8. To fetch a field we can use :

$query = \Drupal::database()->query('SELECT myfield from my_table where
  field1 = :value1 AND field2 = :value2', array(
    ':value1' => $condition1,
    ':value2' => $condition2,
  )
);
$data = $query->fetchField();

Now we can checkout the select, update, and delete operations in Drupal 8. For a field selection use,

$query = \Drupal::database()->select('table_name', 'alias')
  ->fields('alias', ['field1', field2])
  ->condition('field3', $condition);
$results = $query->execute();
while ($content = $results->fetchAssoc()) {
  // Operations using $content.
}

For a single field selection we can use $last_paper_id = $last_paper->fetchField();

For update query execution in Drupal 8, we can use,

$table = 'table_name';
\Drupal::database()->update($table)
  ->fields(array('field1' => $value1, 'field2' => $value2))
  ->condition('field3', $condition1)
  ->condition('field4', $condition2)
  ->execute();

For content deletion,

$query = \Drupal::database()->delete('table_name');
  $query->condition('field1', $condition1);
  $query->condition('field2', $condition2);
  $query->execute();

Now checkout other database statements in Drupal 8 from this link!

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