MySQL 如何对 2 个以上的表进行 LEFT JOIN？
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How to do LEFT JOIN with more than 2 tables?
提问by aleafonso
Currently I am doing this query:
目前我正在做这个查询：
select a.x, b.x, c.x
from number as a, customer as b, numbergroup as c
where a.b = b.b and a.c = c.c and c.b = b.b
However, I want to retrieve records from table "a" even if "a.c = null", which is not retrieved due to the join between "a" and "c".
但是，即使“ac = null”，由于“a”和“c”之间的连接而未检索到，我也想从表“a”中检索记录。
I have found information about left joinbut I don't know how to do it when the query involves more than two tables like in this case.
我找到了有关的信息left join，但当查询涉及两个以上的表时，我不知道该怎么做，就像在这种情况下一样。
回答by Chris J
select a.x, b.x, c.x
from number as a
left join customer as b on a.b = b.b
left join numbergroup as c on a.c = c.c and c.b = b.b
