我如何在mysql中查询两个不同的表

Question

我如何验证两个查询,如果第一个查询是NULL继续第二个查询？

第一查询:

 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

   $query1 = "SELECT max(logs) as logs,id FROM table1 WHERE 
 message NOT LIKE '[ SYSTEM%'";
$query2 = SELECT max(logs) as logs,id FROM table2 WHERE 
 message LIKE '[ SYSTEM%'";
if(mysql_query($query1)) {
    $result = mysql_query($query1);
} else {
   $result = mysql_query($query2);
}