如何从多个表中按最新日期记录排序？

Question

This is my full code:

<?php $sid = $_SESSION['userid'];
$stmt = $pdo->prepare("
    SELECT tableA.*, tableB.*, tableC.*
    FROM tableA
    LEFT JOIN tableB
    ON tableA.tableAuserid = tableB.tableAuserid
    LEFT JOIN tableC
    ON tableA.tableAuserid = tableC.tableCuserid
    WHERE tableA.tableAuserid = ?
    ;
");
$stmt->bindParam(1, $sid, PDO::PARAM_INT);
$stmt->execute();
$columns = $stmt->fetchAll();

foreach($columns as $column):
$tableAdate = $column['tableAdate'];
$tableBdate = $column['tableBdate'];
$tableCdate = $column['tableCdate'];
    if ($tableAdate): ?>
        <div><?php echo $tableAdate; ?></div>
    <?php endif;
    if ($tableBdate): ?>
        <div><?php echo $tableBdate; ?></div>
    <?php endif;
    if ($tableCdate): ?>
        <div><?php echo $tableCdate; ?></div>
    <?php endif;
endforeach; ?>

My 3 database tables are: tableA :

tableAid | tableAuserid | tableAdate
    1    |     44       | 2018-07-13 11:09:11
    2    |     44       | 2019-05-23 01:21:29

tableB :

tableBid | tableBuserid | tableBdate
    1    |     44       | 2019-08-11 17:41:01

And tableC :

tableCid | tableCuserid | tableCdate
    1    |     44       | 2014-03-14 09:18:16

This is the result that's currently being echoed from my code:

2018-07-13 11:09:11
2019-08-11 17:41:01
2014-03-14 09:18:16
2019-05-23 01:21:29
2019-08-11 17:41:01
2014-03-14 09:18:16

But this is the result I want achieved from the code:

2019-08-11 17:41:01 (tableB)
2019-05-23 01:21:29 (tableA)
2018-07-13 11:09:11 (tableA)
2014-03-14 09:18:16 (tableC)

Basically each record must be retrieved with no duplicate values, result must be determined by the $_SESSION['userid'] variable, ORDER arrangement of SQL code must be by the latest date DESC of all dates combined from all 3 tables. How would I accomplish this?

Answer 1

Feel like I am missing some nuance of the question but perhaps not. Lot's of ways to accomplish this.

The following UNION allows for a fair amount of flexibility, that is, the ability to refine criteria per table and still sort on the SQL side of things.

SELECT tId, tUserId, tDate FROM tableA WHERE tUserId = ?
UNION ALL 
SELECT tId, tUserId, tDate FROM tableB WHERE tUserId = ?
UNION ALL
SELECT tId, tUserId, tDate FROM tableC WHERE tUserId = ?
ORDER BY tDate DESC;

I honestly don't write many of these. Maybe in large part because of ORMs (something to look into), or as the conversation has leaned towards, design. Your first take with the left join is the format of probably 95% of the queries I write. Anyway though, there is no reason not to use a union for certain reporting needs. Maybe even create a view *gasp* .

Answer 2

first your SQL is not correct tableB dose not have the column tableB.tableAuserid

  SELECT tableA.*, tableB.*, tableC.*
  FROM tableA
  LEFT JOIN tableB
  ON tableA.tableAuserid = tableB.tableBuserid
  LEFT JOIN tableC
  ON tableA.tableAuserid = tableC.tableCuserid
  WHERE tableA.tableAuserid = 44
  ORDER BY tableAdate desc, tableBdate desc, tableCdate DESC