Question

我有两张桌子：

table1        table2
column id     column id   column value
1             1           count_20
2             1           count_30
3             2           count_20
4             2           count_50
...           2           count_200
              3           count_30
              3           count_50
              3           count_200
              4           count_130
              ...         ...

我想构建一个查询，从table1, column id中选择每一行，从MAX中选择相应column value的{{1}}值并生成table2在DESC列中缩写为int。

所以输出应该是：

value

我已尝试table1.id value 2 count_200 3 count_200 4 count_130 1 count_30 ... ...但是，对于JOIN中的每个value (count_%)，我都会从table2获得相应的id。

table1

输出：

SELECT table1.id, table2.id, table2.value FROM table1
LEFT JOIN table2
ON table2.id=table1.id
WHERE table1.id<'100'
ORDER BY
CASE value
  WHEN 'count_20' THEN '20' 
END DESC,
CASE value
  WHEN 'count_30' THEN '30' 
END DESC,
CASE value
  WHEN 'count_50' THEN '50' 
END DESC,
CASE value
  WHEN 'count_130' THEN '130' 
END DESC,
CASE value
  WHEN 'count_200' THEN '200' 
END DESC;

任何帮助都将不胜感激。

Answer 1

尝试一下：

select t2.id, 
'count_' + cast(max(cast(replace(t2.value, 'count_', '') as int)) varchar) intValue
from table1 t1
join table2 t2 on t1.id = t2.id
group by t2.id
order by max(cast(replace(t2.value, 'count_', '') as int)) desc

这导致：

+----+-----------+
| ID |   VALUE   |
+----+-----------+
|  2 | count_200 |
|  3 | count_200 |
|  4 | count_130 |
|  1 | count_30  |
+----+-----------+

小提琴here。

Answer 2

http://www.w3schools.com/sql/sql_distinct.asp 看一下这个。这只会显示值。

MySQL 5.5从table2中为table1中的每个唯一id选择MAX

2 个答案: