Question

我正在尝试计算以下三个结果的总和，但我只计算一个结果。

$sql = "(SELECT COUNT(*) FROM  table1 WHERE somecondition)
UNION
(SELECT COUNT(*) FROM  table2 WHERE somecondition)
UNION
(SELECT COUNT(*) FROM  table3 WHERE somecondition)";

任何人都可以帮忙。谢谢

Answer 1

您的查询将返回三行，其中包含三个单独的计数。

你想要的是

  select sum(c) from (
      (SELECT COUNT(*) AS c FROM  table1 WHERE somecondition)
      UNION
      (SELECT COUNT(*) FROM  table2 WHERE somecondition)
      UNION
      (SELECT COUNT(*) FROM  table3 WHERE somecondition)
  ) all_three

Answer 2

你可以尝试这样的事情......

SELECT sum(
 ( SELECT count(*) from table1)
+ ( SELECT count(*) from table2)
+ ( SELECT count(*) from table3)
+ ( SELECT count(*) from table4) )as total from dual

Answer 3

如果您正在寻找每个表的计数作为不同的字段..

SELECT (SELECT count(*) FROM table_1) As first_count,
       (SELECT count(*) FROM table_2) As second_count,   
        (SELECT count(*) FROM table_3) As third_count

如果想要总计所有3个表的所有计数，那么

SELECT SUM ((SELECT count(*) FROM table_1) +
       (SELECT count(*) FROM table_2) +
        (SELECT count(*) FROM table_3) ) AS total_count

Answer 4

您的查询将返回3行 - 每个表用于表。

请改用此查询：

$sql = "SELECT SUM(C) FROM(
(SELECT COUNT(*) as C FROM  table1 WHERE somecondition)
UNION
(SELECT COUNT(*) as C FROM  table2 WHERE somecondition)
UNION
(SELECT COUNT(*) as C FROM  table3 WHERE somecondition)
)";

（您需要根据您使用的数据库调整查询）

select count（*）不能给出正确的计数

4 个答案: