Question

我试图在sql developer（emp table）中得到这个结果：

TOTAL       1980       1981      1982     1983
-------- --------- --------- --------- ---------
14            1        10         2        1

但我得到了：

TOTAL       1980       1981      1982     1983
-------- --------- --------- --------- ---------
13            1        10         2        1

指望整个桌子给我14：

SELECT COUNT(*) FROM EMP;

为什么这种情况下的计数会返回13而不是14？

SELECT COUNT(*) TOTAL,
SUM(DECODE(EXTRACT(YEAR FROM HIREDATE),1980,COUNT(*))) "1980",
SUM(DECODE(EXTRACT(YEAR FROM HIREDATE),1981,COUNT(*))) "1981",
SUM(DECODE(EXTRACT(YEAR FROM HIREDATE),1982,COUNT(*))) "1982",
SUM(DECODE(EXTRACT(YEAR FROM HIREDATE),1983,COUNT(*))) "1983"
FROM EMP GROUP BY HIREDATE;

Answer 1

我认为你想要条件聚合：

SELECT COUNT(*) TOTAL,
       SUM(CASE WHEN EXTRACT(YEAR FROM HIREDATE) = 1980 THEN 1 ELSE 0 END) as "1980",
       SUM(CASE WHEN EXTRACT(YEAR FROM HIREDATE) = 1981 THEN 1 ELSE 0 END) as "198`",
       SUM(CASE WHEN EXTRACT(YEAR FROM HIREDATE) = 1982 THEN 1 ELSE 0 END) as "1982",
       SUM(CASE WHEN EXTRACT(YEAR FROM HIREDATE) = 1983 THEN 1 ELSE 0 END) as "1983"
FROM EMP;

注意：

无需GROUP BY HIREDATE。您似乎只想要一行输出。
DECODE()是特定于Oracle的。条件表达式的ANSI标准是CASE。
您在COUNT(*)内嵌套了聚合函数（SUM()）。这是导致问题的原因。此版本应解决此问题。

Count（*）在sql developer（ORACLE）中返回（行号-1）

1 个答案: