如果在另一个表中找到记录，则从表中选择 [英] Select from table if record found in another table

问题描述

我需要从表1中选择一些行，要说是否在表2中找到了一个值.因此，我想检查是否在表2中找到了该值(我将从命令行输入该值)，然后选择行从Table1，如果不是，我想从另一个表中选择行. 我尝试了CASE，但是只有当您想检查一个表中的值时，我才能从CASE中获得结果.有什么主意吗?

I need to select some rows from Table 1 lets say if a value is found in Table 2. So I want to check if the value (I will enter the value from command line) is found in Table 2 and then select rows from Table1, if not I want to select rows from another table. I tried CASE but from what I got that works only if you want to check for value within one table. Any idea?

推荐答案

您可以执行以下操作:

-- If value is found in table2, select from table1
select * -- <- use padding if necessary 
  from table1
 where exists (select 1
                 from table2
                where myField = value)

union all

-- If value is not found in table2, select from another_Table
select * -- <- use padding if necessary
  from another_Table
 where not exists (select 1
                     from table2
                    where myField = value)

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