mysql - SQL 合并行求和

Question

我正在尝试对从 UNION 中的不同 SQL 查询获得的两行求和，这可能吗？我所能实现的只是两个单独的行，但我无法对它们求和，数据库引擎一直告诉我 *) FROM(SUM 旁边的部分)附近的语法有错误...

这是查询:

SELECT * FROM

(SELECT COUNT(*) as cntclients                                                                                               
   FROM                                                                                                                      
   (SELECT DISTINCT clientkey AS clients                                                                                     
      FROM <table>
     WHERE <conditions...>)                                                                                                                 
   ) AS clients                                                                                                              
) cntclients

UNION

(SELECT SUM(occurrences) AS cntclientsad                                                    
   FROM <table2>
   WHERE <conditions...>                                     
)

例如，这让我感到震惊:

cntclients
----------
901
50

在第一行中添加 SELECT SUM(*) FROM 而不是 SELECT * FROM，并用括号将两个查询括起来只会抛出上述错误...

我愿意

cntclients <- or whatever name...
----------
951

知道这个总和应该如何计算吗？

Answer 1

您实际上不需要为此使用 UNION - 您可以手动将它们添加在一起:

SELECT a.countKey + b.sumOccur as total
FROM (SELECT COUNT(DISINCT clientkey) as countKey
      FROM <table>
      WHERE <conditions>) as a
CROSS JOIN (SELECT SUM(occurrences) as sumOccur
            FROM <table2>
            WHERE <conditions>) as b