SQL查询，关联查询的区别 （LEFT JOIN 、LEFT OUTER JOIN、INNER JOIN）

 CREATE TABLE #a(f1 VARCHAR(30),    f2 VARCHAR(40) )
 CREATE TABLE #b(f1 VARCHAR(30),    f2 VARCHAR(40) )
 ------------------------------------------------
 INSERT INTO #a(f1,f2)VALUES('','a1')
 INSERT INTO #a(f1,f2)VALUES('','a2')
 INSERT INTO #a(f1,f2)VALUES('','a3')
 INSERT INTO #a(f1,f2)VALUES('','a4')
 -------------------------------------
 INSERT INTO #b(f1,f2)VaLUES('','b1')
 INSERT INTO #b(f1,f2)VaLUES('','b2')
 --INSERT INTO #b(f1,f2)VALUES('3','b3')
 --INSERT INTO #b(f1,f2)VaLUES('4','b4')
 SELECT a.*,b.*
 FROM #a AS a LEFT JOIN #b AS b ON a.f1 = b.f1
 --
 SELECT a.*,b.*
 FROM #a AS a LEFT OUTER JOIN #b AS b ON a.f1 = b.f1
 -----------
 SELECT a.*,b.*
 FROM #a AS a , #b AS b WHERE  a.f1 = b.f1
 --
 SELECT a.*,b.*
 FROM #a AS a INNER JOIN #b AS b ON a.f1 = b.f1