CREATE TABLE t1
 (
 a varchar(2) PRIMARY KEY,
 B varchar(2),
 c varchar(2)
 )
 INSERT INTO t1
 VALUES('a1','b1','c1')
 
 CREATE TABLE t2
 (
 a  varchar(2) ,
 d varchar(2) PRIMARY KEY,
 e varchar(2) ,
 f varchar(2) 
 )
 INSERT INTO t2
 VALUES( 'a1','d1','e1','f1'),( 'a1','d2','e1','f1')
 
 
 SELECT DISTINCT t1.a,b,c,e,f FROM t1 LEFT JOIN t2 ON t1.a=t2.a

------解决方案--------------------
探讨

SELECT DISTINCT t1.a,b,c,e,f FROM t1 LEFT JOIN t2 ON t1.a=t2.a


------解决方案--------------------
楼上正解，不过表2中的a不是索引的话，数据多的话，查询可能会慢哦