I have a table a, which contains columns a1 and a2.
我有一个表a，其中包含列a1和a2。
I have a table b, which contains columns b1 and b2.
我有一个表b，其中包含b1和b2列。
I want to left join b to a on condition1 if a2 is null and on condition2 if a2 is not null.
如果a2为null，我想将join b连接到on条件1;如果a2不为null，我想将条件2连接到条件2。
How can i construct this query?
我该如何构建此查询？
1 个解决方案
#1
1
If I understand correctly:
如果我理解正确：
proc sql;
select . . .
from a left join
b
on (a2 is null and condition1) or
(a2 is not null and condition2);
This is a direct translation of your requirements. In general, the following often has better performance because this can make better use of indexes (depending on the nature of the conditions):
这是您的要求的直接翻译。通常，以下通常具有更好的性能，因为这可以更好地使用索引（取决于条件的性质）：
proc sql;
select a.*, coalesce(b1.b2, b2.b2) as b2
from a left join
b b1
on (a2 is null and condition1) left join
b b2
on (a2 is not null and condition2);
#1
1
If I understand correctly:
如果我理解正确：
proc sql;
select . . .
from a left join
b
on (a2 is null and condition1) or
(a2 is not null and condition2);
This is a direct translation of your requirements. In general, the following often has better performance because this can make better use of indexes (depending on the nature of the conditions):
这是您的要求的直接翻译。通常，以下通常具有更好的性能，因为这可以更好地使用索引（取决于条件的性质）：
proc sql;
select a.*, coalesce(b1.b2, b2.b2) as b2
from a left join
b b1
on (a2 is null and condition1) left join
b b2
on (a2 is not null and condition2);