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：

TOKEN=

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;

db<>fiddle demo

您无法在同一级别（SELECT引用已定义的列，但是使用CROSS APPLY / LATERAL JOIN可以创建一系列计算列，而无需使用子查询。

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