SQL 使用 3 列在 2 个表之间进行左连接并连接到 Oracle 上的第三个表
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Left join between 2 tables using 3 columns and joing to a third table on Oracle
提问by Mr S
i am using Oracle and need to left join 2 tables (which are actually the same table with alias) based on 3 columns and then join with a third table. What should be the best syntax?
我正在使用 Oracle 并且需要基于 3 列离开连接 2 个表（实际上是具有别名的同一个表），然后与第三个表连接。最好的语法应该是什么？
Select table_3.column_x
From (table_1 left join table_2
Using (column_1 , column_2 , column_3)), table_3
Where Table_2.column_1 = table_3.column_1
Should I use ‘,' on the ‘using statement or ‘AND'? Where exactly should I insert the table_3 statement even if it is not used on the left join?
我应该在“using 语句”还是“AND”上使用“,”？即使在左连接中没有使用 table_3 语句，我究竟应该在哪里插入它？
回答by Erkan Haspulat
Using ANSI SQL:
使用 ANSI SQL：
select * from
TABLE1 "TABLE1"
left join TABLE1 "TABLE2" on(TABLE1.c1 = TABLE2.C1 and TABLE1.c2 = TABLE2.C2)
left join TABLE3 "TABLE3" on(TABLE1.c3 = TABLE3.c3)
Using Oracle Join Syntax you have:
使用 Oracle 连接语法，您有：
select * from TABLE1 "TABLE1", TABLE1 "TABLE2", TABLE3 "TABLE3"
where
TABLE1.c1 = TABLE2.c1 (+)
and TABLE1.c2 = TABLE2.c2 (+)
and TABLE1.c3 = TABLE3.c3 (+)
(+) here represents the left join. I personally prefer ANSI SQL way. It seems cleaner to me. Your join predicates might not be the same with my example, keep that in mind.
(+) 这里代表左连接。我个人更喜欢 ANSI SQL 方式。对我来说似乎更干净。您的连接谓词可能与我的示例不同，请记住这一点。
