用条件计数行

Question

我在桌子上工作＆＃34;船舶＆＃34;像这样：

shipid
container1
container2

始终填充

shipid 和 container1 ， container2 是可选的。

这是我现在的查询：

SELECT COUNT(container1) FROM table

我怎样才能实现此查询计算容器2的数量？！

它必须是由这两个查询组成的联合查询：

SELECT COUNT(container1) FROM table
SELECT COUNT(container2) FROM table WHERE container2!=''

感谢任何提示！

Answer 1

SELECT COUNT(container1) FROM table
UNION
SELECT COUNT(container2) FROM table

Answer 2

您可以使用SUM

SELECT 
     SUM(container1) AS c1
    ,SUM(CASE WHEN container2 IS NOT NULL THEN 1 ELSE 0 END) AS c2
FROM ships

Answer 3

要添加到先前的答案，您可以执行此操作以获得1个结果中的计数。

 SELECT SUM(count) FROM
  (
   SELECT COUNT(container1) as count FROM table
   UNION ALL
   SELECT COUNT(container2) as count FROM table
  ) as a

或者你可以这样做：

SELECT COUNT(*) FROM
  (
   SELECT container1  FROM table
   UNION ALL
   SELECT container2  FROM table
  ) as a