Question

我正在尝试根据主键列以降序查询表。

以下是查询：

SELECT * FROM fdmsus_demo.vitalstats
ORDER BY 
( SELECT `COLUMN_NAME`
FROM `information_schema`.`COLUMNS`
WHERE (`TABLE_SCHEMA` = 'fdmsus_demo')
  AND (`TABLE_NAME` = 'vitalstats')
  AND (`COLUMN_KEY` = 'PRI') 
 ) DESC LIMIT 10;

我希望此查询以降序返回行。但是它没有按预期工作。我觉得DESC没有应用于查询。我以这种方式编写查询的原因是，我想在我的Java代码中使用此查询，它将参数化函数如：

public void myFunction(String dbName, String tableName);

因为在运行时我不知道表的主键是什么。但是我只提供2个参数dbname和tablename。因此，使用以下子查询获取主键列名称：

( SELECT `COLUMN_NAME`
FROM `information_schema`.`COLUMNS`
WHERE (`TABLE_SCHEMA` = 'fdmsus_demo')
  AND (`TABLE_NAME` = 'vitalstats')
  AND (`COLUMN_KEY` = 'PRI') 
 )

以上查询相当于：

SELECT * FROM fdmsus_demo.vitalstats ORDER BY VitalsMasterKey DESC LIMIT 10;

返回的结果按预期降序排列。

任何人都可以帮我纠正查询并按降序输出。任何帮助将不胜感激。

感谢。

Answer 1

尝试将desc应用于内部查询。

Answer 2

试试这个会起作用

set @Query1=Concat('SELECT * FROM fdmsus_demo.vitalstats ORDER BY ', (SELECT `COLUMN_NAME`
    FROM `information_schema`.`COLUMNS`
    WHERE (`TABLE_SCHEMA` = 'fdmsus_demo')
      AND (`TABLE_NAME` = 'vitalstats')
      AND (`COLUMN_KEY` = 'PRI')),' desc limit 10');

 PREPARE stmt FROM @Query1; 
 EXECUTE stmt;

Answer 3

您必须编写准备声明

SET @col = '';
SELECT `COLUMN_NAME` INTO @col
FROM `information_schema`.`COLUMNS`
WHERE (`TABLE_SCHEMA` = 'fdmsus_demo')
  AND (`TABLE_NAME` = 'vitalstats')
  AND (`COLUMN_KEY` = 'PRI');
SET @q = CONCAT('SELECT * FROM fdmsus_demo.vitalstats ORDER BY ',@col,' DESC LIMIT 10');
PREPARE stmt FROM @q;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Answer 4

SELECT * FROM fdmsus_demo.vitalstats
ORDER BY 
( SELECT `COLUMN_NAME`
FROM `information_schema`.`COLUMNS`
WHERE (`TABLE_SCHEMA` = 'fdmsus_demo')
  AND (`TABLE_NAME` = 'vitalstats')
  AND (`COLUMN_KEY` = 'PRI') 
ORDER BY COLUMN_NAME DESC LIMIT 10;
) ORDER BY COLUMN_NAME DESC LIMIT 10;

这应该做。您缺少需要在内部查询中应用desc函数。

MySQL按主要顺序以DESC顺序动态排序

4 个答案: