Question

我有两个按ID链接的表格（下面的简化示例）：

Table 1

ID     NAME
1      John
2      Frank

Table 2

ID     DAY     TIME_FROM    TIME_TO
1      Sun     8:00         15:00
1      Mon     8:00         15:00
1      Tue     NULL         NULL
1      Wed     NULL         NULL
1      Thu     NULL         NULL
1      Fri     8:00         15:00
1      Sat     8:00         15:00
2      Sun     8:00         15:00
...

我想要的是一个查询，理想地返回一个字段中每个ID的缩写天数，如下所示：

ID     NAME    DAYS 
1      John    S M F S 
2      Frank   S M T W T F S

或者也许：

ID     NAME    SUN    MON   TUE    
1      John    TRUE   TRUE  FALSE
2      Frank   TRUE   TRUE  TRUE

如果可能的话，首选解决方案。

Answer 1

使用GROUP_CONCAT()功能

SELECT t1.ID,t1.NAME,
       GROUP_CONCAT(`DAY` SEPERATOR ' ') as `DAYS`
FROM table1 t1
INNER JOIN table2 t2
ON t1.ID=t2.ID
GROUP BY t1.ID,t1.NAME

Answer 2

试试这个：

首先解决方案：

SELECT T1.ID,T1.Name,
        GROUP_CONCAT(T2.`DAY` SEPARATOR ' ') as Day
FROM Table1 T1 JOIN
     Table2 T2 ON T1.Id=T2.Id
GROUP BY T1.ID,T1.Name

结果：

ID  NAME    DAY
1   John    Thu Fri Sat Sun Mon Tue Wed
2   Frank   Sun

注意：使用3个字母可避免Sat和Sun之间的混淆。查看SQL Fiddle中的结果。

第二个解决方案：

SELECT T1.ID,T1.Name,
        MAX(CASE WHEN (COALESCE(TIME_FROM,TIME_TO) IS NOT NULL  AND `DAY` ='Sun') THEN 'TRUE' ELSE 'FALSE' END) as SUN,
        MAX(CASE WHEN (COALESCE(TIME_FROM,TIME_TO) IS NOT NULL  AND `DAY` ='Mon') THEN 'TRUE' ELSE 'FALSE' END) as MON,
        MAX(CASE WHEN (COALESCE(TIME_FROM,TIME_TO) IS NOT NULL  AND `DAY` ='Tue') THEN 'TRUE' ELSE 'FALSE' END) as TUE,
        MAX(CASE WHEN (COALESCE(TIME_FROM,TIME_TO) IS NOT NULL  AND `DAY` ='Wed') THEN 'TRUE' ELSE 'FALSE' END) as WED,
        MAX(CASE WHEN (COALESCE(TIME_FROM,TIME_TO) IS NOT NULL  AND `DAY` ='Thu') THEN 'TRUE' ELSE 'FALSE' END) as THU,
    MAX(CASE WHEN (COALESCE(TIME_FROM,TIME_TO) IS NOT NULL  AND `DAY` ='Fri') THEN 'TRUE' ELSE 'FALSE' END) as FRI,
    MAX(CASE WHEN (COALESCE(TIME_FROM,TIME_TO) IS NOT NULL  AND `DAY` ='Sat') THEN 'TRUE' ELSE 'FALSE' END) as SAT
FROM Table1 T1 JOIN
     Table2 T2 ON T1.Id=T2.Id
GROUP BY T1.ID,T1.Name

<强>解释

COALESCE将有助于检查TIME_FROM和TIME_TO NULL。

结果（使用给定示例）：

ID  NAME    SUN     MON     TUE     WED     THU     FRI     SAT
1   John    TRUE    TRUE    FALSE   FALSE   FALSE   TRUE    TRUE
2   Frank   TRUE    FALSE   FALSE   FALSE   FALSE   FALSE   FALSE

结果为SQL Fiddle。

如何在MYSQL中选择多个行值作为列值？

2 个答案: