Question

我有超过35列的表，前20列是固定的，每列中的列号不同。我需要从表格中选择最后10列，我该如何实现？就像这个查询返回前20条记录

一样

select * from table1 limit 10;

我想对列做同样的事情我的意思是在查询中返回列名，然后在另一个查询中使用这些名称，如：

SELECT (SELECT column_name FROM INFORMATION_SCHEMA.Columns WHERE TABLE_NAME = 'table1' ) FROM table1;

Answer 1

您可以通过准备好的陈述来实现这一目标。您的查询将如下所示：

SELECT 
  CONCAT('SELECT ', 
         GROUP_CONCAT(COLUMN_NAME), 
         ' FROM test') 
FROM 
  (SELECT 
    COLUMN_NAME, 
    ORDINAL_POSITION 
  FROM 
    INFORMATION_SCHEMA.COLUMNS 
  WHERE 
    TABLE_SCHEMA='test' 
    AND 
    TABLE_NAME='test' 
  ORDER BY 
    ORDINAL_POSITION DESC LIMIT 10) AS ord_desc 
ORDER BY 
  ord_desc.ORDINAL_POSITION

- 这将创建一个包含以下内容的SQL：

SELECT date,title FROM test

（在上面的示例中，我在选择中有2列，可在此部分进行调整：ORDER BY ORDINAL_POSITION DESC LIMIT 10）

所以你需要做的就是准备这个陈述。就我而言：

SQL：

mysql> set @sql=(SELECT CONCAT('SELECT ', GROUP_CONCAT(COLUMN_NAME), ' FROM test') FROM (SELECT COLUMN_NAME, ORDINAL_POSITION FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA='test' AND TABLE_NAME='test' ORDER BY ORDINAL_POSITION DESC LIMIT 2) AS ord_desc ORDER BY ord_desc.ORDINAL_POSITION);
Query OK, 0 rows affected (0.02 sec)

准备：

mysql> prepare stmt from @sql;
Query OK, 0 rows affected (0.00 sec)

结果：

mysql> execute stmt;
+------------+--------------+
| date       | title        |
+------------+--------------+
| 2014-02-04 | my event 001 |
| 2014-02-04 | my event 002 |
| 2014-02-05 | my event 003 |
| 2014-02-05 | my event 004 |
| 2014-02-05 | my event 005 |
| 2014-02-07 | my event 006 |
| 2014-02-07 | my event 007 |
+------------+--------------+
7 rows in set (0.00 sec)

从MySQL中选择表的最后N＃列

1 个答案: