Question

我正在尝试从数据库中查询2个表，并希望使用group_concat（）只有一行结果。但是通过我创建的查询，我得到的数据库不只是一次，而是多次，我不知道为什么：

SELECT a.owner,
       group_concat(causConc, '') AS attributes,
       group_concat(causConc2, '') AS reqs
FROM (SELECT a.owner,
             '{' || key || ',' || group_concat(value, ',') || ';' || '}' AS causConc
      FROM attributes a
      WHERE a.owner = 162012
      GROUP BY a.owner,
               key) a
INNER JOIN (SELECT owner,
             '{' || key || ',' || group_concat(value, ',') || ';' || '}' AS causConc2
      FROM reqs r
      WHERE r.owner = 162012
      GROUP BY r.owner,
               key) r 
ON a.owner = r.owner
GROUP BY a.owner

任何人都可以告诉我为什么我多次获得这些数据库的命令？

提前致谢！：）

Answer 1

连接计算来自两个源的匹配行的所有可能组合。

要仅连接两个来源的行，请使用compound query：

SELECT owner,
       group_concat(causConc, '') AS attributes,
       group_concat(causConc2, '') AS reqs
FROM (SELECT owner, causConc, NULL AS causConc2
      FROM (... first subquery ...)
      UNION ALL
      SELECT owner, NULL, causConc2
      FROM (... second subquery ...))
GROUP BY owner;

group_concat（）在多个表的多个列上

1 个答案: