结合想要不同过滤的最大值的sql查询

Question

我有两个MySQL查询从几乎相同的查询中查找MAX（）值。我希望有一种方法可以将查询结合起来以获得更好的性能。

SELECT name, MAX(version) AS highest 
FROM publish 
WHERE name IN ('alpha', 'beta') AND deprecated = TRUE 
GROUP BY name; 

SELECT name, MAX(version) AS closed 
FROM publish 
WHERE name IN ('alpha', 'beta') AND open = FALSE 
GROUP BY name; 

该模式非常简单。对于这个简单的例子，它看起来像

CREATE TABLE publish 
(
    name CHAR(36) NOT NULL, 
    version INT NOT NULL, 
    deprecated TINYINT NOT NULL, 
    open TINYINT DEFAULT 0 NOT NULL, 
    PRIMARY KEY (name, version), 
); 
CREATE INDEX open ON publish (open); 
CREATE INDEX deprecated ON publish (deprecated); 

Answer 1

可以使用条件聚集到你的查询

SELECT name, MAX(case when open = FALSE then version end) AS closed, 
MAX(case when deprecated = TRUE then version end) AS highest 
FROM publish 
WHERE name IN ('alpha', 'beta') 
GROUP BY name; 

Answer 2

结合你可以尝试UNION

SELECT name, MAX(version) AS highest 
FROM publish 
WHERE name IN ('alpha', 'beta') AND deprecated = TRUE 
GROUP BY name 
UNION ALL 
SELECT name, MAX(version) AS closed 
FROM publish 
WHERE name IN ('alpha', 'beta') AND open = FALSE 
GROUP BY name; 

但优化的解决方案是使用CASE（用于条件功能）

SELECT name, MAX(case when deprecated = TRUE then version end) AS highest, 
MAX(case when open = FALSE then version end) AS closed, 
FROM publish 
WHERE name IN ('alpha', 'beta') 
GROUP BY name; 

Answer 3

这应该工作

使用UNION（如果你不想重复行）或UNION ALL（当您想检索所有行）

我将使用UNION：

(SELECT name, MAX(version) AS highest FROM publish WHERE deprecated = TRUE) 
UNION 
(SELECT name, MAX(version) AS closed FROM publish WHERE open = FALSE) 
WHERE name IN ('alpha', 'beta') GROUP BY name; 

干杯;）