我认为MysqL中没有简单的方法。一种方法是通过为按rating_name分组的每一行生成一个行号,然后仅选择row_number为2或更少的行。在大多数数据库中,您可以使用以下方法进行此操作:
SELECT * FROM (
SELECT
rating_name,
etc...,
ROW_NUMBER() OVER (PARTITION BY rating_name ORDER BY good) AS rn
FROM your_table
) T1
WHERE rn <= 2
不幸的是,MysqL不支持该ROW_NUMBER
语法。但是,您可以ROW_NUMBER
使用变量进行模拟:
SELECT
rating_name, id_markets, good, neutral, bad
FROM (
SELECT
*,
@rn := CASE WHEN @prev_rating_name = rating_name THEN @rn + 1 ELSE 1 END AS rn,
@prev_rating_name := rating_name
FROM (
SELECT
rating_name,
id_markets,
SUM(COALESCE(rating_good, 0)) AS good,
SUM(COALESCE(rating_neutral, 0)) AS neutral,
SUM(COALESCE(rating_bad, 0)) AS bad
FROM zzratings
WHERE rating_year = YEAR(CURDATE()) AND rating_week = WEEK(CURDATE(), 1)
GROUP BY rating_name, id_markets
) AS T1, (SELECT @prev_rating_name := '', @rn := 0) AS vars
ORDER BY rating_name, good DESC
) AS T2
WHERE rn <= 2
ORDER BY rating_name, good DESC
对测试数据运行时的结果:
法国1 2 0 0
法国2 1 0 0
爱尔兰1 4 2 0
爱尔兰21 3 1 0
波兰1 3 1 0
波兰2 1 0 0