如何通过解码找到小于？

Question

ORA-00907: missing right parenthesis

00907\. 00000 -  "missing right parenthesis"

---

SELECT last_name
      ,salary
      ,DECODE(salary, salary <  6000, 0.36,
                      salary <  8000, 0.38,
                      salary < 10000, 0.4,
                      salary < 12000, 0.42,
                      salary < 14000, 0.44,
                      salary < 16000, 0.45) as "TAX RATE"
  FROM employees;

Answer 1

不要让你的生活成为痛苦。 使用CASE表达式而不是DECODE 。

select case when salary <  6000 then 0.36
            when salary <  8000 then 0.38
            ...
            when salary < 16000 then 0.45
            else null
       end as tax_rate
from employees

如果你想用DECODE来做，你会使用SIGN function （检查薪水是否低于一定数量），然后根据需要嵌套尽可能多的DECODE 。 这行得通，但维护起来是一场噩梦。

我没有你的表，所以我会尝试使用 Scott 的emp来说明它：

SQL> select ename, sal,
  2    decode(sign(sal - 1000), -1, 'less than 1000',
  3      decode(sign(sal - 1500), -1, 'less than 1500',
  4        decode(sign(sal - 2000), -1, 'less than 2000'))
  5          ) rate
  6  from emp;

ENAME             SAL RATE
---------- ---------- --------------
SMITH             840 less than 1000
ALLEN            1600 less than 2000
WARD             1250 less than 1500
JONES            2975
MARTIN           1250 less than 1500
BLAKE            2850
CLARK            2450
SCOTT            3000
KING             5000
<snip>

如果将它与CASE进行比较，差异将非常明显：

SQL> select ename, sal,
  2    case when sal < 1000 then 'less than 1000'
  3         when sal < 1500 then 'less than 1500'
  4         when sal < 2000 then 'less than 2000'
  5    end rate
  6  from emp;

ENAME             SAL RATE
---------- ---------- --------------
SMITH             840 less than 1000
ALLEN            1600 less than 2000
WARD             1250 less than 1500
JONES            2975
MARTIN           1250 less than 1500
<snip>