sql - 选择常量作为伪列并对伪列进行算术运算

Question

我想做这样的事情:

select 999 as price, 0.1 as tax_rate, 
price*tax_rate as tax_amount, tax_amount+price as total
from Dual;

在 Oracle 数据库上。

Answer 1

您可以使用CROSS APPLY(Oracle 12c):

select price, tax_rate, tax_amount, tax_amount+price as total
from Dual
CROSS APPLY (SELECT 999 AS price, 0.1 AS tax_rate FROM dual) s
CROSS APPLY (SELECT price*tax_rate AS tax_amount FROM dual) s2;

select price, tax_rate, tax_amount, tax_amount+price as total
from Dual
,LATERAL (SELECT 999 AS price, 0.1 AS tax_rate FROM dual) s
,LATERAL (SELECT price*tax_rate AS tax_amount FROM dual) s2;

<强> db<>fiddle demo

您无法引用同一级别的定义列(SELECT)，但使用CROSS APPLY/LATERAL JOIN您可以创建一个链不使用子查询的计算列。

类似的方法:PostgreSQL using a calculated column in the same query