如何正确使用 group_concat 连接 MYSQL 中的 Join 查询结果？

Question

我编写了以下 MYSQL 查询，Mysql 版本是 8.0.18-commercial

SELECT p.server, 'Type_ABC' AS Check_Type, COALESCE(vmtable.res) AS result
FROM server p 
INNER JOIN truns t ON t.oq_id = p.oq_id
AND t.id = (SELECT t2.id FROM truns t2 WHERE t2.oq_id = p.oq_id order by t2.created_at desc limit 1 )
INNER JOIN qvuln_info vmtable ON vmtable.run_id = t.id 
LEFT JOIN qvuln_info_data vmtableinfo ON vmtableinfo.qid = vmtable.qid   
WHERE p.server regexp 'server1';

我从上面的查询中得到以下输出：

Hostname   Check_Type result
server1    Type_ABC   Result 1
server1    Type_ABC   Result 2
server1    Type_ABC   Result 3
server1    Type_ABC   Result 4

我想连接结果，以便输出如下所示：

Hostname   Check_Type  result
server1    Type_ABC    Result 1,,Result 2,,Result 3,,Result 4

为实现上述输出，我编写了以下查询，但出现语法错误：

SELECT p.server, 'Type1' AS Check_Type, 
GROUP_CONCAT((COALESCE(vmtable.res) AS result) SEPARATOR ', ')
FROM server p 
INNER JOIN truns t ON t.oq_id = p.oq_id
AND t.id = (SELECT t2.id FROM truns t2 WHERE t2.oq_id = p.oq_id order by t2.created_at desc limit 1 )
INNER JOIN qvuln_info vmtable ON vmtable.run_id = t.id 
LEFT JOIN qvuln_info_data vmtableinfo ON vmtableinfo.qid = vmtable.qid   
WHERE p.server regexp 'server1';

如何正确使用 GROUP_CONCAT 和 COALESCE？

Answer 1

您的查询缺少 GROUP BY 子句；你需要GROUP BY p.server。请注意，您的 COALESCE 实际上并没有做任何事情，因为如果值为 NULL，您还没有提供要替换的值，所以您最好将其省略（因为 GROUP_CONCAT忽略 NULL 值，当 vmtable.res 为 NULL 时，这将防止任何值出现在 result 中）。您的查询应如下所示：

SELECT p.server, 'Type1' AS Check_Type, 
       GROUP_CONCAT(vmtable.res SEPARATOR ', ') AS result
FROM server p 
INNER JOIN truns t ON t.oq_id = p.oq_id
AND t.id = (SELECT t2.id FROM truns t2 WHERE t2.oq_id = p.oq_id order by t2.created_at desc limit 1 )
INNER JOIN qvuln_info vmtable ON vmtable.run_id = t.id 
LEFT JOIN qvuln_info_data vmtableinfo ON vmtableinfo.qid = vmtable.qid   
WHERE p.server regexp 'server1'
GROUP BY p.server

另请注意 AS result 应该在 GROUP_CONCAT 之外。

如何正确使用 group_concat 连接 MYSQL 中的 Join 查询结果？

How to correctly use group_concat to concatenate Join query result in MYSQL?

mysql

join

select

inner-join

coalesce