PostgreSQL视图:在另一个计算字段中引用一个计算字段 [英] PostgreSQL Views: Referencing one calculated field in another calculated field
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问题描述
我与#1895500 ,但使用PostgreSQL而不是MySQL。
I have the same question as #1895500, but with PostgreSQL not MySQL.
如何定义具有计算字段的视图,例如:
How can I define a view that has a calculated field, for example:
(mytable.col1 * 2) AS times_two
...并创建基于第一个字段的另一个计算字段:
... and create another calculated field that's based on the first one:
(times_two * 2) AS times_four
...?
推荐答案
根据formla的沉重程度,您可以使用子查询:
Depending on how heavy the formla is, you could use a subquery:
select inner.*, times_two * 2 from
(select mycol * 2 as times_two from table) sub
或重写计算:
select mycol * 2, mycol * 2 * 2 from table
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