mysql - 复杂的？ MySQL查询

Question

我有一个包含列、id、日期、estValue 和 Gradeid 的表。每个成绩 ID 大约有 12 条记录，大约有 10 个不同的成绩，总共大约 120 条记录[给出或接受]我需要从数据库中创建一个选择，为我提供一个如下所示的结果集:

date    |gradeid1 |gradeid2 |gradeid3 3|etc...
01/01/01|estValue1|estValue2||estValue3|etc....
01/01/02|estValue1|estValue2||estValue3|etc....

我有一个可以选择一条记录的查询，但我需要将它们全部按日期排序:

select eh.id, eh.date as wdate,
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '1') as '1',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '2') as '2',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '3') as '3',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '4') as '4',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '5') as '5',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '6') as '6',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '7') as '7',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '8') as '8',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '9') as '9',
    (select estValue from nas_estimatehistory where `date` like '2011-03-%' and gradeid = '10') as '10'
from nas_estimatehistory eh  
group by wdate 
order by `wdate` asc
limit 1;

它返回几乎我需要的内容，但只有 1 行，如果我删除限制，那么我每个月都会得到一行 [12 行]，但所有列值都是相同的 [它们应该都不同]，即每行和列中的 estValue 应该是唯一的值...

我不确定最好的方法是什么。

-谢谢 -肖恩

Answer 1

Cross-tabulation关键是:使用aggregate function和 IF 函数。

SELECT eh.date AS wdate,
    GROUP_CONCAT(IF(gradeid=1,estValue,NULL)) as `1`,
    GROUP_CONCAT(IF(gradeid=2,estValue,NULL)) as `2`,
    GROUP_CONCAT(IF(gradeid=3,estValue,NULL)) as `3`,
    GROUP_CONCAT(IF(gradeid=4,estValue,NULL)) as `4`,
    GROUP_CONCAT(IF(gradeid=5,estValue,NULL)) as `5`,
    GROUP_CONCAT(IF(gradeid=6,estValue,NULL)) as `6`,
    GROUP_CONCAT(IF(gradeid=7,estValue,NULL)) as `7`,
    GROUP_CONCAT(IF(gradeid=8,estValue,NULL)) as `8`,
    GROUP_CONCAT(IF(gradeid=9,estValue,NULL)) as `9`,
    GROUP_CONCAT(IF(gradeid=10,estValue,NULL)) as `10`
FROM nas_estimatehistory eh  
GROUP BY wdate 
ORDER BY `wdate` ASC;

MAX 或 MIN 也可能是合适的聚合函数。