MYSQL选择计数关系除法

Question

我在mysql中有这个表  1.是否可以选择一个计数 - 所有相同的entity_id，其中field_tags_tid = 2和field_tags_tid = 7

在此示例中，结果为1，因为只有entity_id = 6匹配field_tags_tid = 2且field_tags_tid = 7

Answer 1

此问题通常称为Relational Division

SELECT  entity_ID
FROM    tableName
WHERE   field_tags_ID IN (2,7)
GROUP   BY entity_ID
HAVING  COUNT(*) = 2

如果field_tags_ID对entity_ID每个DISTINCT强制执行唯一性，则需要SELECT entity_ID FROM tableName WHERE field_tags_ID IN (2,7) GROUP BY entity_ID HAVING COUNT(DISTINCT field_tags_ID) = 2 个关键字。否则，保持原样，

SELECT  COUNT(*) totalCOunt
FROM
(
    SELECT  entity_ID
    FROM    tableName
    WHERE   field_tags_tid IN (2,7)
    GROUP   BY entity_ID
    HAVING  COUNT(DISTINCT field_tags_tid) = 2
) s

• SQLFiddle Demo
• SQL of Relational Division

更新1

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• SQLFiddle Demo