Question

我有以下查询：

SELECT a.topicID, d.catalogFileID, d.catalogFileExtension, a.sortorder
FROM catalog_topics a
LEFT JOIN catalog_files_join b ON a.catalogID = b.foreignKey
LEFT JOIN catalog_files_join c ON c.foreignKey = b.catalogFileID
LEFT JOIN catalog_files d ON d.catalogFileID = b.catalogFileID
WHERE b.fileTypeID = 'gvl401'
AND c.fileTypeID = 'gvl25'
AND a.topicid = 'top340'

取出：

topicID  catalogFileID  catalogFileExtension  sortorder
top340   cfil1070       jpg                   5
top340   cfil958        jpg                   7
top340   cfil958        jpg                   7
top340   cfil956        jpg                   6
top340   cfil864        jpg                   4
top340   cfil862        jpg                   3

但是我不想回到多行，而是想获得一行（最小排序顺序）。所以在这种情况下是最后一行。

我尝试了以下查询：

SELECT a.topicID, d.catalogFileID, d.catalogFileExtension, min( a.sortorder )
AS smallestorder
FROM catalog_topics a
LEFT JOIN catalog_files_join b ON a.catalogID = b.foreignKey
LEFT JOIN catalog_files_join c ON c.foreignKey = b.catalogFileID
LEFT JOIN catalog_files d ON d.catalogFileID = b.catalogFileID
WHERE b.fileTypeID = 'gvl401'
AND c.fileTypeID = 'gvl25'
AND a.topicid = 'top340'
GROUP BY a.topicid

取出：

topicID  catalogFileID  catalogFileExtension  smallestorder
top340   cfil1070       jpg                   3

那是错的。即使我得到了最小的排序顺序......我没有得到与之对应的行。

如果通过将第一个查询的结果存储在一个单独的表中来更容易解决这个问题，那么我也会对此持开放态度。

Answer 1

SELECT ... ORDER BY a.sortorder LIMIT 1

Answer 2

您可以使用ORDER BY和LIMIT代替GROUP BY：

SELECT a.topicID, d.catalogFileID, d.catalogFileExtension, a.sortorder
FROM catalog_topics a
LEFT JOIN catalog_files_join b ON a.catalogID = b.foreignKey
LEFT JOIN catalog_files_join c ON c.foreignKey = b.catalogFileID
LEFT JOIN catalog_files d ON d.catalogFileID = b.catalogFileID
WHERE b.fileTypeID = 'gvl401'
AND c.fileTypeID = 'gvl25'
AND a.topicid = 'top340'
ORDER BY a.sortorder ASC
LIMIT 1

从group by的查询中选择最小值

2 个答案: