mysql - 如何进行mysql子查询

Question

我有一个大表，现在表按日期细分为几个

例如

原表

UserLoginTable
+---------+------------+---------+
| UserID  | LoginTime  | others  |
+---------+------------+---------+
|  1      | 2013-03-12 | ....    |
+---------+------------+---------+
|  2      | 2013-05-12 | ....    |
+---------+------------+---------+
|  1      | 2013-06-12 | ....    |
+---------+------------+---------+
|  ...    | ...        | ....    |   
+---------+------------+---------+

现在表格是：

UserLoginTable_Date(yyyyMM)

用户登录表_201303

+---------+------------+---------+
| UserID  | LoginTime  | others  |
+---------+------------+---------+
|  1      | 2013-03-12 | ....    |
+---------+------------+---------+

用户登录表_201304

+---------+------------+---------+
| UserID  | LoginTime  | others  |  //this table is not have UserID=1
+---------+------------+---------+
|  2      | 2013-04-01 | ....    |
+---------+------------+---------+

我用了

select count(*) from UserLoginTable_201307 where UserID=1
select count(*) from UserLoginTable_201306 where UserID=1
...

所以我想知道如何通过一个 sql 显示这种格式

+--------------+ 
| UserInYear   |  
+--------------+ 
|  201303      |  //here dose find User in 201304
+--------------+
|  201306      |  
+--------------+
|  ....        |  
+--------------+

最佳效率点。谢谢。

Answer 1

用于UNION ALL：

SELECT COUNT(*) AS UserInYear FROM UserLoginTable_201307 WHERE UserID = 1
UNION ALL
SELECT COUNT(*) FROM UserLoginTable_201306 WHERE UserID = 1

如果任何年份的 UserInYear 存在重复值，则将UNION ALL全部显示，而UNION不会显示。所以使用UNION ALL.

Answer 2

尝试union all如下使用

select count(*) as UserInYear from UserLoginTable_201307 where UserID=1
union all
select count(*) from UserLoginTable_201306 where UserID=1

注意：union all不会消除重复。如果您不想重复，则必须使用unioninsetad。

Answer 3

子查询的一个例子：

SELECT column_name, column_name1, column_number
FROM their_table
WHERE column_number = (SELECT MAX(column_number) FROM the_other_table);

假设 column_name 作为 customerNumber，column_name1 作为 checkNumber，column_number 作为 amo