Question

我在SQL中有两个count语句，我希望得到它们之间的区别。我正在尝试这样的事情。

SELECT  'Customers After', SUM(Counts) Counts
FROM
(SELECT 'Customers Before', COUNT(*) AS Counts FROM CUSTOM3
MINUS
SELECT  'Customers to be', COUNT(*) AS Counts FROM
CUSTOM3 a
WHERE 
    a.CUSTOMER_FLAG IS NULL
AND NOT EXISTS (SELECT 1 FROM ACC2 acc WHERE acc.CUSTOMER_ID = a.CUSTOMER_ID)
AND CUST_BQ IS NULL);

但是它只是返回行数，我应该使用什么而不是MINUS，或者我应该如何启动它？

我应该得到这样的东西：

Customers After 15
Customers Before 20
Customers to be 5

Answer 1

使用子查询和案例表达式：

SELECT Customers_before, Customers_after,
       Customers_before - Customers_after As Customers_to_be
FROM (
    SELECT count(*) As Customers_before,
           count( case when a.CUSTOMER_FLAG IS NULL
                       and not exists( 
                            SELECT 1 FROM ACC2 acc 
                            WHERE acc.CUSTOMER_ID = a.CUSTOMER_ID)
                       and CUST_BQ IS NULL
                   then 1 end ) as Customers_after
    FROM CUSTOM3 a
)

Answer 2

执行此操作时：

SELECT 'Customers Before', COUNT(*)
MINUS
SELECT  'Customers to be', COUNT(*)

... minus没有做任何事情，因为第二个查询中的第一列值不相同。即使该字符串相同，您也可以看到相同的数据（如果计数不同）或者没有返回任何行（如果计数相同）。我认为你只是误解了what the minus set operator does。

如果您想要计算差值，则需要减去它们的值：

SELECT  'Customers After',
  (SELECT COUNT(*) FROM CUSTOM3)
  - (SELECT COUNT(*) FROM CUSTOM3 a
      WHERE a.CUSTOMER_FLAG IS NULL
      AND NOT EXISTS (SELECT 1 FROM ACC2 acc WHERE acc.CUSTOMER_ID = a.CUSTOMER_ID)
      AND CUST_BQ IS NULL) Counts
FROM dual;

或仅计算不匹配＆＃39;减去＆＃39;的行数。标准（验证空处理）：

SELECT  'Customers After', COUNT(*) AS Counts
FROM CUSTOM3 a
WHERE NOT (a.CUSTOMER_FLAG IS NULL
AND NOT EXISTS (SELECT 1 FROM ACC2 acc WHERE acc.CUSTOMER_ID = a.CUSTOMER_ID)
AND CUST_BQ IS NULL);

或

SELECT  'Customers After', COUNT(*) AS Counts
FROM CUSTOM3 a
WHERE a.CUSTOMER_FLAG IS NOT NULL
OR EXISTS (SELECT 1 FROM ACC2 acc WHERE acc.CUSTOMER_ID = a.CUSTOMER_ID)
OR CUST_BQ IS NOT NULL;

或者如果您确实想要查看结果集中的所有三个计数，请使用子查询，如@krokodilko所示。

Answer 3

我喜欢使用with的代码，对我来说似乎更清楚：

with cb as (SELECT COUNT(*) AS Counts FROM CUSTOM3),
     ctb as (SELECT COUNT(*) AS Counts FROM CUSTOM3 a
WHERE a.CUSTOMER_FLAG IS NULL
AND NOT EXISTS (SELECT 1 FROM ACC2 acc WHERE acc.CUSTOMER_ID = a.CUSTOMER_ID)
AND CUST_BQ IS NULL)
     select 'Customers Before' as description, counts from cb union all
     select 'Customers to be' as description, counts from ctb union all
     select 'Customers After' as description, cb.counts - ctb.counts as counts from cb, ctb

两个计数语句之间的区别

3 个答案: