现在有两张表table_a和table_b ,其中每张表的数据如下
table_a 表中数据：
Id Name Score
1 a 90
2 b 80
3 c 85
table_b 表中数据：
Id Name Score
2 b 80
3 c 85
4 d 90
(1) left join
<strong></strong><pre class="html" name="code"><span style="font-size:12px;">select a.id,a.name,a.score from table_a a left join table_b b on a.id=b.id;</span>
结果如下：
1 a 90
2 b 80
3 c 85
(2) left outer join
select a.id,a.name,a.score from table_a a left outer join table_b b on a.id=b.id;结果如下：
1 a 90
2 b 80
3 c 85
(3) left semi join
<pre class="html" name="code">select a.id,a.name,a.score from table_a a left semi join table_b b on a.id=b.id;结果如下：
2 b 80
3 c 85
(4) full outer join
select a.id,a.name,a.score from table_a a full outer join table_b b on a.id=b.id;结果如下：
1 a 90
2 b 80
3 c 85
NULL NULL NULL