Question

我有一份日期清单：

1/1/2011
2/2/2011
3/3/2011
4/4/2011
5/5/2011

我需要取出“x”个日期并将其标记为已启用。

=＆GT;得到2个最老的，然后我需要

1/1/2011 - 0 (enabled)
2/2/2011 - 0
3/3/2011 - 1 (disabled)
4/4/2011 - 1
5/5/2011 - 1

=＆GT;得到3个最老的，然后我需要

1/1/2011 - 0 (enabled)
2/2/2011 - 0
3/3/2011 - 0
4/4/2011 - 1  (disabled)
5/5/2011 - 1

我可以这样：

select * from table order by date_column limit 2; - for 2 entries.

select * from table order by date_column limit 3; - for 3 entries.

但是如何在单个查询中根据日期值添加1或0？有什么办法可以在一个查询中完成吗？

Answer 1

此查询的工作原理是假设日期是唯一的：

SELECT
    A.date_column,ISNULL(B.date_column) enabled
FROM
    `table` LEFT JOIN
    (SELECT date_column FROM `table` ORDER BY date_column LIMIT 3) B
    USING (date_column);

如果表格中的日期不唯一，请尝试以下查询：

SELECT
    A.date_column,
    IF(ISNULL(B.date_column)=0,'0 (enabled)','1 (disabled)') status
FROM
    `table` A LEFT JOIN
    (
        SELECT date_column
        FROM (SELECT DISTINCT date_column FROM `table` ORDER BY date_column) AA
        LIMIT 3
    ) B
    USING (date_column);

试一试!!!

这次我尝试了你的数据：

use junk
drop table `table`;
create table `table` (date_column DATE);
INSERT INTO `table` VALUES
('2011-01-01'),
('2011-02-02'),
('2011-03-03'),
('2011-04-04'),
('2011-05-05');
SELECT * FROM `table`;
SELECT

    A.date_column,
    IF(ISNULL(B.date_column)=0,'0 (enabled)','1 (disabled)') status
FROM
    `table` A LEFT JOIN
    (SELECT date_column FROM
        (SELECT DISTINCT date_column FROM `table` ORDER BY date_column) AA
    LIMIT 3) B
USING (date_column);

这是输出：

mysql> use junk
Database changed
mysql> drop table `table`;
Query OK, 0 rows affected (0.02 sec)

mysql> create table `table` (date_column DATE);
Query OK, 0 rows affected (0.06 sec)

mysql> INSERT INTO `table` VALUES
    -> ('2011-01-01'),('2011-02-02'),('2011-03-03'),
    -> ('2011-04-04'),('2011-05-05');
Query OK, 5 rows affected (0.05 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM `table`;
+-------------+
| date_column |
+-------------+
| 2011-01-01  |
| 2011-02-02  |
| 2011-03-03  |
| 2011-04-04  |
| 2011-05-05  |
+-------------+
5 rows in set (0.00 sec)

mysql> SELECT
    ->
    ->     A.date_column,
    ->     IF(ISNULL(B.date_column)=0,'0 (enabled)','1 (disabled)') status
    -> FROM
    ->     `table` A LEFT JOIN
    ->     (SELECT date_column FROM
    ->         (SELECT DISTINCT date_column FROM `table` ORDER BY date_column) AA
    LIMIT 3) B
    ->     LIMIT 3) B
    -> USING (date_column);
+-------------+--------------+
| date_column | status       |
+-------------+--------------+
| 2011-01-01  | 0 (enabled)  |
| 2011-02-02  | 0 (enabled)  |
| 2011-03-03  | 0 (enabled)  |
| 2011-04-04  | 1 (disabled) |
| 2011-05-05  | 1 (disabled) |
+-------------+--------------+
5 rows in set (0.00 sec)

Answer 2

select 
  T1.DateColumn,
   Case when Isnull(T2.DateColumn) 
    then 1
    Else 0 end 
  as disabled
 from table T1 left outer join
  (select dateColumn from table 
   order by date_column asc limit 3) T2
  On t1.dateColumn =t2.DateColumn
 Order by t1.datecolumn asc

单个查询以获取日期并将日期标记为已启用

2 个答案: