如何使mysql子查询

Question

我有一个大的表，现在该表被细分为几个日期

例如，

原始表

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

现在的表是：

UserLoginTable_Date(yyyyMM) 

UserLoginTable_201303

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

UserLoginTable_201304

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

我曾经

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

所以我想Kown如何通过一个SQL

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

的最佳效率点，以示对这种格式。谢谢。

Answer 1

尝试使用union all如下

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。如果您不想复制，则必须使用union insetad。

Answer 2

使用UNION ALL为：

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

如果没有为UserInYear重复值，任何一年UNION ALL将显示所有，而UNION不会显示。所以使用UNION ALL。

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); 

假设列名作为customerNumber之和 column_name1作为checkNumber和 COLUMN_NUMBER栏作为AMO