Question

我在向SQL查询中包含ORDER和LIMIT时遇到问题。

$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){

上面的脚本工作正常。但我想限制数据的数量（我只需要每个表中的最后一个）。我试着通过

来做

ORDER BY date_time DESC LIMIT 0,1

在sprintf查询中

但它不想工作。当我添加ORDER等。我有答案

致命错误：在“while（（$ row_5_2 ...”
中的非对象上调用成员函数fetch_assoc（）

任何人都可以提供帮助吗？

Answer 1

查看您的代码，您可能会收到以下错误（但请检查以确定）：

Incorrect usage of UNION and ORDER BY

如果是这样，那是因为你没有括号。请参阅UNION的手册：

要将ORDER BY或LIMIT应用于单个SELECT，请将该子句放在括起SELECT的括号内：
(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);

使用sprintf进行ORDER，LIMIT和查询

1 个答案: