Question

将3个SQL查询合并到一个简单的查询中，我遇到了一个很大的问题。有没有办法将这些简单的SQL查询加入一个？

QUERY1：

SELECT COUNT(FieldID) AS "CountA"
FROM table WHERE Rezervovany = 0 AND Prodany = 0

QUERY2：

SELECT COUNT(FieldID) AS "CountB"
FROM table WHERE Rezervovany = 1 AND Prodany = 0

QUERY3：

SELECT COUNT(FieldID) AS "CountC"
FROM table WHERE Prodany = 1

Answer 1

您可以将条件放在汇总case函数内的count子句中：

SELECT Count(CASE 
               WHEN rezervovany = 0 AND prodany = 0 THEN fieldid 
               ELSE NULL 
             END) AS "CountA", 
       Count(CASE 
               WHEN rezervovany = 1 AND prodany = 0 THEN fieldid 
               ELSE NULL 
             END) AS "CountB", 
       Count(CASE 
               WHEN prodany = 1 THEN fieldid 
               ELSE NULL 
             END) AS "CountC" 
FROM   table

请注意，count仅计算非空值。

Answer 2

如果你想一个接一个地获取行，你可以这样做：

SELECT COUNT(FieldID) AS "CountA" FROM table WHERE Rezervovany = 0 AND Prodany = 0
union
SELECT COUNT(FieldID) AS "CountB" FROM table WHERE Rezervovany = 1 AND Prodany = 0
union
SELECT COUNT(FieldID) AS "CountC" FROM table WHERE Prodany = 1

Reference (for MySQL)

一个SQL查询中的不同结果的多个WHERE条件

2 个答案: