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如何将多条查询同一表不同分组结果的SQL语句合并成一条语句执行?


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小浪云 2024-11-11 45

如何将多条查询同一表不同分组结果的SQL语句合并成一条语句执行?

mysql语句合并优化

问题:给定多条查询同一表不同分组结果的sql语句,能否将其合并成一条sql语句执行?

select *, count(*) as count from t_search where mark = 'a' group by title order by count desc limit 0, 20  select *, count(*) as count from t_search where mark = 'b' group by title order by count desc limit 0, 20  select *, count(*) as count from t_search where mark = 'c' group by title order by count desc limit 0, 20  ...
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总共有24条sql语句,每个查询的mark字段从a到z,每条语句查询20条结果。

解答:

方法1:mysql 8.0+

使用with子句和窗口函数:

with ranked_data as (     select *,            count(*) over (partition by title, mark) as count,            row_number() over (partition by mark order by count(*) desc) as row_num     from t_search     where mark between 'a' and 'z'     group by title, mark ) select * from ranked_data where row_num <= 20 order by mark, count desc;
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方法2:mysql 8.0以下

使用变量和子查询:

SELECT * FROM (     SELECT *,            @rank := IF(@prev_mark = mark, @rank + 1, 1) AS rank,            @prev_mark := mark,            COUNT(*) AS count     FROM t_search     JOIN (SELECT @rank := 0, @prev_mark := '') AS vars     WHERE mark BETWEEN 'a' AND 'z'     GROUP BY title, mark     ORDER BY mark, count DESC ) AS ranked_data WHERE rank <= 20 ORDER BY mark, count DESC;
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