SQL查询,关联查询的区别 (LEFT JOIN 、LEFT OUTER JOIN、INNER JOIN)
1 CREATE TABLE #a(f1 VARCHAR(30), f2 VARCHAR(40) ) 2 CREATE TABLE #b(f1 VARCHAR(30), f2 VARCHAR(40) ) 3 ------------------------------------------------ 4 INSERT INTO #a(f1,f2)VALUES('1','a1') 5 INSERT INTO #a(f1,f2)VALUES('2','a2') 6 INSERT INTO #a(f1,f2)VALUES('3','a3') 7 INSERT INTO #a(f1,f2)VALUES('4','a4') 8 ------------------------------------- 9 INSERT INTO #b(f1,f2)VaLUES('1','b1') 10 INSERT INTO #b(f1,f2)VaLUES('2','b2') 11 --INSERT INTO #b(f1,f2)VALUES('3','b3') 12 --INSERT INTO #b(f1,f2)VaLUES('4','b4') 13 SELECT a.*,b.* 14 FROM #a AS a LEFT JOIN #b AS b ON a.f1 = b.f1 15 -- 16 SELECT a.*,b.* 17 FROM #a AS a LEFT OUTER JOIN #b AS b ON a.f1 = b.f1 18 ----------- 19 SELECT a.*,b.* 20 FROM #a AS a , #b AS b WHERE a.f1 = b.f1 21 -- 22 SELECT a.*,b.* 23 FROM #a AS a INNER JOIN #b AS b ON a.f1 = b.f1