如何在学说中使用左子句？

Question

this is my query for find all records in table and sort from the oldest. I want to limit one column to only 50 characters. I can't find any information how to change this query for use left clause.

    $posts = $ChocoPosts->findBy(array(), array('id' => 'DESC'));

Additionally i tried use clean sql syntax for that, but it's not show any records.

 $conn = $this->getDoctrine()->getManager()->getConnection();
$sql = '
    SELECT id, title, left(content, 45), date_add, img
    FROM choco_posts
    ORDER BY id DESC
    ';
$stmt = $conn->prepare($sql);
$stmt->execute();

$stmt->fetchAll();

I'm using symfony4 ant twig template. I display all records in twig for loop.

Answer 1

You can simply use SUBSTRING statement, as example:

$sql = '
    SELECT id, title, SUBSTRING(content, 1, 45), date_add, img
    FROM choco_posts
    ORDER BY id DESC
    ';

By itself there is little difference, however left can potentially utilize an index while substring cannot.

Hope this help