php - 我如何在mysql中查询两个不同的表

Question

如果第一个查询为 NULL，我如何验证两个查询继续第二个查询？

第一个查询:

 SELECT max(logs) as logs,id FROM table1 WHERE 
 message NOT LIKE "[ SYSTEM%"

第二个查询:

 SELECT max(logs) as logs,id FROM table2 WHERE 
 message LIKE "[ SYSTEM%"

Answer 1

我认为你应该看看你的解释。因为对数据库的查询次数更少 - 更好。在这种情况下，您应该使用联合:

SELECT max(logs) as logs, id, 'table1' type
FROM table1 WHERE message NOT LIKE "[ SYSTEM%"
UNION
SELECT max(logs) as logs, id, 'table2' type
FROM table2 WHERE message LIKE "[ SYSTEM%"
;

按字段类型可以了解从哪个表接收数据。
但是如果你的解释不好，你应该使用单独的查询:

<?php

$dbh = new PDO('mysql:dbname=test;host=127.0.0.1', 'root');

$sth = $dbh->prepare('
    SELECT max(logs) as logs, id
    FROM table1 WHERE message NOT LIKE :like
');
$sth->bindParam(':like', $like, PDO::PARAM_STR);
$sth->execute();
$result = $sth->fetchAll(PDO::FETCH_ASSOC);

if (empty($result)) {
    $sth = $dbh->prepare('
        SELECT max(logs) as logs, id
        FROM table2 WHERE message LIKE :like
    ');
    $sth->bindParam(':like', $like, PDO::PARAM_STR);
    $sth->execute();
    $result = $sth->fetchAll(PDO::FETCH_ASSOC);
}

var_export($result);