MySQL更新并在一条语句中选择

Question

I am attempting to do an UPDATE and a SELECT in the same sql statement. For some reason, the below code is failing.

$sql = "UPDATE mytable SET last_activity=CURRENT_TIMESTAMP, 
info1=:info1, info2=:info2 WHERE id = {$id};";

$sql .= "SELECT id, info1, info2 FROM myTable 
WHERE info1 >=:valueA AND info2>:valueB;"

$stmt = $conn->prepare($sql);
$stmt->bindParam(":info1", $info1);
$stmt->bindParam(":info2", $info2);

$stmt->bindParam(":valueA", $valueA);
$stmt->bindParam(":valueB", $valueB);

$stmt->execute();

$result = $stmt->fetchAll(PDO::FETCH_ASSOC);

echo json_encode($result);

QUESTION: what might I be doing wrong? I have been spending hours on this issue knowing that it's probably a small error right under my nose.

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Edited:

I obtained this error message when loading the page that contains the php code:

Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error' in ajaxCall.php:89 Stack trace: #0 ajaxCall.php(89): PDOStatement->fetchAll(2) #1 {main} thrown in ajaxCall.php on line 89

I am using ajax to call the php page that contains the above code, and when I load the php page from the browser, I get the above error message.

Line 89 is: $result = $stmt->fetchAll(PDO::FETCH_ASSOC);

Answer 1

Since you are running two queries, you need to call nextRowset to access the results from the second one.

So, do it like this:

// code
$stmt->execute();
$stmt->nextRowset();
// code

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When you run two or more queries, you get a multi-rowset result. That means that you get something like this (representation only, not really this) :

Array(
    [0] => rowset1,
    [1] => rowset2,
    ...
)

Since you want the second set -the result from the SELECT -, you can consume the first one by calling nextRowset . That way, you'll be able to fetch the results from the 'important' set.
(Even though 'consume' might not be the right word for this, it fits for understanding purposes)

Answer 2

Executing two queries with one call is only allowed when you are using mysqlnd . Even then, you must have PDO::ATTR_EMULATE_PREPARES set to 1 when using prepared statements. You can set this using:

$conn->setAttribute(PDO::ATTR_EMULATE_PREPARES, 1);

Alternatively, you can use $conn->exec($sql) , which works regardless. However, it will not allow you to bind any data to the executed SQL.

All in all, don't execute multiple queries with one call.