oracle 在选择查询中使用别名
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Use Alias in Select Query
提问by user960567
I need to ask how can use Alias in Select Query,
我需要问如何在选择查询中使用别名，
I need this
我需要这个
SELECT (Complex SubQuery) AS A, (Another Sub Query WHERE ID = A) FROM TABLE
回答by Johan
You cannot do this:
你不可以做这个：
SELECT (Complex SubQuery) AS A, (Another Sub Query WHERE ID = A) FROM TABLE
You can however do this:
但是，您可以这样做：
SELECT (Another Sub Query WHERE ID = A.somecolumn)
FROM table
JOIN SELECT (Complex SubQuery) AS A on (A.X = TABLE.Y)
Or
或者
SELECT (Another Sub Query)
FROM table
WHERE table.afield IN (SELECT Complex SubQuery.otherfield)
The problem is that you cannot refer to aliases like this in the SELECT and WHERE clauses, because they will not have evaluated by the time the select or where part is executed.
You can also use a havingclause, but having clauses do not use indexes and should be avoided if possible.
问题是你不能在 SELECT 和 WHERE 子句中引用这样的别名，因为在执行 select 或 where 部分时它们不会被评估。
您也可以使用having子句，但具有子句不使用索引，应尽可能避免使用。
回答by wqw
You can rewrite your query like this
你可以像这样重写你的查询
SELECT Complex.A, (Another Sub Query WHERE ID = Complex.A)
FROM TABLE
CROSS JOIN ((Complex SubQuery) AS A) Complex
回答by Arbel Sella
Another solution which you can use:
您可以使用的另一种解决方案：
SELECT (Complex SubQuery) AS A, (Another Sub Query WHERE ID = A)
FROM
TABLE MAIN
OUTER APPLY (SELECT (Complex SubQuery) AS A)
