1 到 n 关系中的 MySQL 数据透视表

Question

我有这样的数据 表master_item

+-------+----------+ |item_id|item_name| +-------+----------+ | 001 |车A | | 002 |车B | +-------+----------+

和关系到表进程

+-------+--------+ |proc_id|proc_seq| +-------+--------+ | 001 | 1 | | 001 | 2 | | 001 | 3 | | 001 | 4 | | 001 | 5 | | 002 | 1 | | 002 | 2 | | 002 | 3 | +-------+--------+

当我选择 item_id = 001 时，我想要这样的结果

+-------+---------+-----+------+-----+-----+-----+- -+-----+ |item_id|item_name|proc1|proc2|proc3|proc4|proc5|proc6|proc7| +-------+---------+-----+------+-----+-----+-----+- -+-----+ | 001 |车A | 1 | 2 | 3 | 4 | 5 | | | +-------+---------+-----+------+-----+-----+-----+- -+-----+

产生这个结果的查询是什么？

Answer 1

问题在于PIVOT TABLE类别。

在这里您可以通过下面给出的查询来完成您的结果：

SET @sql := '';
SELECT 
CONCAT('SELECT 
MI.item_id,
MI.item_name,',
GROUP_CONCAT('MAX(CASE WHEN P.proc_seq =', P.proc_seq ,' THEN P.proc_seq END) AS ', 'proc',P.proc_seq,' '),
'FROM master_item MI
INNER JOIN process P ON MI.item_id = P.proc_id
WHERE MI.item_id = 1
GROUP BY P.proc_id') INTO @sql
FROM master_item MI
INNER JOIN process P ON MI.item_id = P.proc_id
WHERE item_id = 1
GROUP BY P.proc_id;


PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE stmt;

WORKING DEMO

但就像我说的，最好在应用程序逻辑中做这种工作。否则单独通过 MySQL 做起来太麻烦了。

编辑：

为了得到每个item_id的结果

SET @sql := '';
SELECT 
CONCAT('SELECT 
MI.item_id,
MI.item_name,',
GROUP_CONCAT('MAX(CASE WHEN P.proc_seq =', P.proc_seq ,' THEN P.proc_seq END) AS ', 'proc',P.proc_seq,' '),
'FROM master_item MI
INNER JOIN process P ON MI.item_id = P.proc_id
GROUP BY P.proc_id') INTO @sql
FROM master_item MI
INNER JOIN process P ON MI.item_id = P.proc_id

WHERE
    item_id = (
        SELECT
            maxProcId.proc_id
        FROM
            (
                SELECT
                    proc_id,
                    COUNT(proc_seq) total
                FROM process
                GROUP BY proc_id
                ORDER BY total DESC
                LIMIT 1
            ) AS maxProcId
    )
GROUP BY
    P.proc_id;


PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE stmt;

Demonstrated here

Answer 2

使用Group_concat，然后将数据拆分到单独的列即可

SELECT t1.*,
      SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(t2.proc_seq), ',', 1), ',', -1) AS proc1, 
      SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(t2.proc_seq), ',', 2), ',', -1) AS proc2, 
      SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(t2.proc_seq), ',', 3), ',', -1) AS proc3, 
      SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(t2.proc_seq), ',', 4), ',', -1) AS proc4, 
      SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(t2.proc_seq), ',', 5), ',', -1) AS proc5
FROM tt1 t1
LEFT JOIN tt2 t2 ON t1.item_id=t2.proc_id