ORDER，LIMIT和使用sprintf查詢

Question

我有包括ORDER和LIMIT到SQL查詢中的問題。

$STH_1 = $DBH_R->query("SELECT table_name       
         FROM information_schema.tables       
         WHERE table_name       
         LIKE 'v_c_ei\_9%' 
         "); 
$stmts_1 = array(); 

//echo "date = ".  $date."<br>";         // $date is today date 
$date_60 = date('Y-m-d', strtotime('-60 day', strtotime($date)));  // $date_60 = today - 60 days 


while (($row_1 = $STH_1 -> fetch_assoc()) !== null){ 

$table_name = $row_1['table_name']; 
$stmts_1[] = sprintf("SELECT * 
         FROM $table_name 
         WHERE (date_time >= '$date_60') AND (ei_code = '1117')  
        ");  
} 

// at this place I need help, I think. I have few data from every query but I want to reduce the number of solutions to 1 per table 

$stmt_1 = implode("\nUNION\n", $stmts_1); 
$stmt_1 .= "\nORDER BY date_time ASC";  
$STH_5_2 = $DBH_R->query($stmt_1);   
while (($row_5_2 = $STH_5_2 -> fetch_assoc()) !== null){ 

上面的腳本工作正常。但我想限制數據的數量（我只需要每個表中的最後一個）。我嘗試通過

ORDER BY date_time DESC LIMIT 0,1 

在sprintf查詢但它不想工作。當我添加ORDER等。我有答案

Fatal error: Call to a member function fetch_assoc() on a non-object in "while (($row_5_2 ..."

任何人都可以幫助嗎？

Answer 1

看你的代碼，這很可能是你很可能得到以下錯誤（但請對此予以肯定）：

 
Incorrect usage of UNION and ORDER BY 

如果是這樣，那是因爲你缺少括號。請參閱UNION的手冊：

To apply ORDER BY or LIMIT to an individual SELECT, place the clause inside the parentheses that enclose the SELECT:

(SELECT a FROM t1 WHERE a=10 AND B=1 ORDER BY a LIMIT 10) 
UNION 
(SELECT a FROM t2 WHERE a=11 AND B=2 ORDER BY a LIMIT 10);