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JOIN语句基础

join test1

#join test1  查询t1、t2表的交集部分
select * from t_test  t1  
inner join t_test2 t2 on t1.id=t2.id;

join test2

#join test2
select * from t_test t1
 right join t_test2 t2 on t1.id=t2.id;

join test3

#join test3
select * from t_test t1 left join t_test2 t2 on t1.id=t2.id;

join test4

#join test4  
select * from t_test t1
    left join t_test2 t2 on t1.id=t2.id
where t2.id is null;

join test5

#join test5
select * from t_test t1
    right join t_test2 t2 on t1.id=t2.id
where t1.id is null;

join test6

#join test6
select * from t_test  t1
      left  join  t_test2 t2 on t1.id=t2.id
union
select * from t_test  t1
                  right   join  t_test2 t2 on t1.id=t2.id;

join test7

#join test7
select * from t_test  t1
                  left  join  t_test2 t2 on t1.id=t2.id
where t2.id is null
union
select * from t_test  t1
                  right   join  t_test2 t2 on t1.id=t2.id
where t1.id is null;

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SQL执行顺序

手写的SQL

select  <distinct  >  <select content>
from  <table name>
 <join type>   on  < join condition>
where
<where condition>
group by  <group by condition>
having <having condition>
order by <order by condition>
limit <limit condition>

手写代码经过MySQL解析器解析成机器识别的SQL

from  <table name>
 <join type>   on  < join condition>
where
<where condition>
group by  <group by condition>
having <having condition>
select  <distinct  >  <select content>
order by <order by condition>
limit <limit condition>

SQL鱼骨图