Question

这个概念是我试图比较2个等值表来查看另一个查询是否具有相同的值，或者它们是否存在于另一个查询中。我加入表格的方式是： “为table1 a选择a.sth，a.sth2，a.st3，b.value，table2 b，其中a.key = b.valkey” 这将导致显示table1的值列，然后显示table2中的列value2，其中键的键相同。现在我有另外2个表包含类似的数据，我想检查我的查询结果是否存在于我将为其他表构建的查询中，如： “为table3 a选择a.sth，a.sth2，a.st3，b.value，table4 b，其中a.key = b.valkey”

我想到这样做的唯一方法是使用嵌套的隐式游标。例如：

BEGIN
     FOR item IN (select a.sth, a.sth2, a.st3, b.value for table1 a, table2 b where a.key = b.valkey)
     LOOP
Begin
FOR item2 IN (select a.sth, a.sth2, a.st3, b.value for table3 a, table4 b where a.key = b.valkey)
  LOOP
    Begin
if (item1.sth = item2.sth) and (item1.sth2 = item2.sth2) and (item1.sth3 = item2.sth3) and (item1.value = item2.value) Then
dbms_output.put_line("Found and value is the same");
Elsif (item1.sth = item2.sth) and (item1.sth2 = item2.sth2) and (item1.sth3 = item2.sth3) and Not (item1.value = item2.value) Then 
dbms_output.put_line("Found but value is different");
Exception When no_data_found then
dbms_output.put_line("item1 was not found in table3");
End;
  END LOOP;
End;
 END LOOP;
 END;

以上只是我想做的伪代码。我可以做这样的事情，还是有更好的性能，我可以使用？我期待着你的建议。

Answer 1

你不需要游标。通常，基于集合的代码将更好地工作。查询看起来像这样：

select coalesce(a.key, b.valkey) as thekey,
       a.sth, a.sth2, a.st3, b.value
       (case when a.key is null then 'Not found in a'
             when b.key is null then 'Not found in b'
             when (a.sth = b.sth) and (a.sth2 = b.sth2) and (a.sth3 = b.sth3) and
                  (a.value = b.value)
             then 'Found and same'
             when (a.sth = b.sth) and (a.sth2 = b.sth2) and (a.sth3 = b.sth3) and
                  (a.value <> b.value)
             then 'Found and different'
             else 'Other!!!'
        end)
from table1 a full outer join
     table2 b 
     on a.key = b.valkey

Oracle Compare 2 equijoined表

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