MySQL – 选择count大于1的数据
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我有下表:
+-------------------------------------+----------------------------------------------------------------+
| keyword | landing_page |
+-------------------------------------+----------------------------------------------------------------+
| orange | https://www.example.co.uk/ |
| apple | https://www.example.co.uk/ |
| pear | https://www.example.co.uk/ |
| apple | https://www.example.co.uk/ |
| apple | https://www.example.co.uk/landing-page |
+-------------------------------------+----------------------------------------------------------------+
我想选择具有多个不同着陆页的任何关键字,因此在此示例中,我们将返回:
apple, https://www.example.co.uk
apple, https://www.example.co.uk/landing-page
我怎样才能用MySQL实现这个目标?
更新:
我尝试了以下但它似乎不起作用:
select keyword, count(landing_page)
from search_data
group by keyword
having count(distinct landing_page) > 1;
解决方法:
您尝试的查询是解决方案的一部分.将该查询用作内联视图,以标识具有多个目标网页的关键字.将该查询的结果连接回原始表.
SELECT t.keyword
, t.landing_page
FROM ( -- keyword with more than one landing page
SELECT r.keyword
FROM search_data r
GROUP BY r.keyword
HAVING COUNT(DISTINCT r.landing_page) > 1
) s
JOIN search_data t
ON t.keyword = s.keyword
GROUP BY t.keyword, t.landing_page
ORDER BY t.keyword, t.landing_page
这不是唯一的方法.还有其他查询模式也将返回等效结果.作为另一种方法的示例,使用相关子查询来检查表中具有相同关键字但具有不同landing_page的另一行的存在:
SELECT DISTINCT t.keyword, t.landing_page
FROM search_data t
WHERE EXISTS ( SELECT 1
FROM search_data r
WHERE r.keyword = t.keyword
AND NOT ( r.landing_page <=> t.landing_page )
)
ORDER BY t.keyword, t.landing_page
跟进
演示设置:
CREATE TABLE search_data (keyword VARCHAR(10), landing_page VARCHAR(80))
;
CREATE INDEX search_data_IX1 ON search_data (keyword, landing_page)
;
INSERT INTO search_data (keyword, landing_page) VALUES
('orange','https://www.example.co.uk/')
,('apple','https://www.example.co.uk/')
,('pear','https://www.example.co.uk/')
,('apple','https://www.example.co.uk/')
,('apple','https://www.example.co.uk/landing-page')
;
EXPLAIN查询1
EXPLAIN
SELECT t.keyword
, t.landing_page
FROM ( -- keyword with more than one landing page
SELECT r.keyword
FROM search_data r
GROUP BY r.keyword
HAVING COUNT(DISTINCT r.landing_page) > 1
) s
JOIN search_data t
ON t.keyword = s.keyword
GROUP BY t.keyword, t.landing_page
ORDER BY t.keyword, t.landing_page
-- id select_type table type possible_keys key key_len ref rows Extra
-- ------ ----------- ---------- ------ --------------- --------------- ------- ------ ------ ------------------------
-- 1 PRIMARY <derived2> system (NULL) (NULL) (NULL) (NULL) 1
-- 1 PRIMARY t ref search_data_IX1 search_data_IX1 13 const 2 Using where; Using index
-- 2 DERIVED r index (NULL) search_data_IX1 96 (NULL) 5 Using index
执行查询1
SELECT t.keyword
, t.landing_page
FROM ( -- keyword with more than one landing page
SELECT r.keyword
FROM search_data r
GROUP BY r.keyword
HAVING COUNT(DISTINCT r.landing_page) > 1
) s
JOIN search_data t
ON t.keyword = s.keyword
GROUP BY t.keyword, t.landing_page
ORDER BY t.keyword, t.landing_page
-- keyword landing_page
-- ------- --------------------------------------
-- apple https://www.example.co.uk/
-- apple https://www.example.co.uk/landing-page
解释查询2
EXPLAIN
SELECT DISTINCT t.keyword, t.landing_page
FROM search_data t
WHERE EXISTS ( SELECT 1
FROM search_data r
WHERE r.keyword = t.keyword
AND NOT ( r.landing_page <=> t.landing_page )
)
ORDER BY t.keyword, t.landing_page
-- id select_type table type possible_keys key key_len ref rows Extra
-- ------ ------------------ ------ ------ --------------- --------------- ------- -------------- ------ -------------------------------------
-- 1 PRIMARY t range (NULL) search_data_IX1 96 (NULL) 6 Using where; Using index for group-by
-- 2 DEPENDENT SUBQUERY r ref search_data_IX1 search_data_IX1 13 test.t.keyword 1 Using where; Using index
执行查询2
SELECT DISTINCT t.keyword, t.landing_page
FROM search_data t
WHERE EXISTS ( SELECT 1
FROM search_data r
WHERE r.keyword = t.keyword
AND NOT ( r.landing_page <=> t.landing_page )
)
ORDER BY t.keyword, t.landing_page
-- keyword landing_page
-- ------- --------------------------------------
-- apple https://www.example.co.uk/
-- apple https://www.example.co.uk/landing-page
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