使用单个 PL SQL 查询返回多个计数答案

【问题标题】：Return multiple counts with single PL SQL Query使用单个 PL SQL 查询返回多个计数
【发布时间】：2010-10-20 13:19:34
【问题描述】：

我有以下两个返回计数的 PL/SQL Oracle 查询：

SELECT count(*)
  INTO counter_for_x
  FROM Table_Name
 WHERE Column_Name = 'X';

SELECT count(*)
  INTO counter_for_y
  FROM Table_Name
 WHERE Column_Name = 'Y';

是否可以编写一个查询来返回计数并填充相应的计数器变量？

【问题讨论】：

标签： sql oracle plsql

【解决方案1】：

SELECT  (
        SELECT COUNT(*)
        FROM   table_name
        WHERE  column_name = 'X'
        ),
        (
        SELECT COUNT(*)
        FROM   table_name
        WHERE  column_name = 'Y'
        )
INTO    counter_for_x, counter_for_y
FROM    dual

【讨论】：

【解决方案2】：

你可以，但我不会这样做......

select nvl(sum(decode(column_name,'X',1,0)),0), nvl(sum(decode(column_name,'Y',1,0)),0)
  into counter_for_x, counter_for_y
  from table_name
  where column_name in ('X', 'Y');

【讨论】：

【解决方案3】：

另一种方式。

SELECT
   Max(CASE WHEN Column_Name = 'X' THEN Count ELSE NULL END) AS Count_X ,
   MAX(CASE WHEN Column_Name = 'Y' THEN Count ELSE NULL END) AS Count_Y
FROM
(
    SELECT count(*) as Count, Column_Name
    FROM Table_Name
    Where Column_Name in ('X', 'Y')
    Group By Column_Name
) AS InnerTable

【讨论】：

【解决方案4】：

这样就可以了：

select count(decode(column_name,'X',1)) x_count
,      count(decode(column_name,'Y',1)) y_count
into   counter_for_x, counter_for_y
from   table_name
where  column_name in ('X','Y');

或者如果您更喜欢使用 CASE：

select count(case when column_name = 'X' then 1 end) x_count
,      count(case when column_name = 'Y' then 1 end) y_count
into   counter_for_x, counter_for_y
from   table_name
where  column_name in ('X','Y');

【讨论】：