我有一个 select 语句调用同一个函数两次以返回两个不同的列，因为同一个函数被调用两次，它会产生性能问题。
我只想调用函数一次并将其值复制到另一列。在 Oracle 中有可能吗？
SELECT ID
,PKGRESTFUNCTION.getBlock(table.ID, table.TYPE) "BLOCK"
,PKGRESTFUNCTION.getBlock(table.ID, table.TYPE) "MASK"
from table
where ID=condition;
最佳答案
您可以使用 with clause一次获取数据
with block as (
select PKGRESTFUNCTION.getBlock(table.ID, table.TYPE) as block
from table
where ID=condition;
) select ID, block.block as "BLOCK" , block.block as "MASK" from block
The WITH clause, or subquery factoring clause, is part of the SQL-99 standard and was added into the Oracle SQL syntax in Oracle 9.2. The WITH clause may be processed as an inline view or resolved as a temporary table. The advantage of the latter is that repeated references to the subquery may be more efficient as the data is easily retrieved from the temporary table, rather than being requeried by each reference. You should assess the performance implications of the WITH clause on a case-by-case basis.
关于oracle - SQL避免在select语句中调用同一个函数两次，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53387661/