Oracle SELECT - 一列的别名作为另一列的输入
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Oracle SELECT - alias of one column as an input to another
提问by Senthu Sivasambu
Folks I found similar but not exact questions on this forum - pardon me if i have not done enough searching for them. This is my question..in Oracle
我在这个论坛上发现了类似但不准确的问题 - 如果我没有对它们进行足够的搜索，请原谅我。这是我的问题……在 Oracle 中
select ( t.value*2) as inst2, (inst2 * 3) as inst3
from table t;
the thinking behind is if f() = t.value*2is an expensive call, then we do not need to make that twice..or is there an alternative query structure i could use (I am trying to achieve this in CTAS)
背后的想法是，如果f() = t.value*2是一个昂贵的调用，那么我们不需要进行两次......或者是否有我可以使用的替代查询结构（我试图在 CTAS 中实现这一点）
thanks in advance.
提前致谢。
回答by Thomas Tschernich
Another option:
另外一个选项：
with cte as (
select t.value*2 as inst2
)
select
cte.inst2,
(cte.inst2*3) as inst3
from cte
This is actually the same as in bluefeet's reply, but I would consider it easier to understand with the with-syntax.
这实际上与 bluefeet 的回复相同，但我认为使用with-syntax更容易理解。
回答by Taryn
If you want to use an alias in the second calculation, then you will want to use a subquery:
如果要在第二个计算中使用别名，则需要使用子查询：
select inst2,
(inst2 * 3) as inst3
from
(
select t.value*2 as inst2
from table t
)
