SQL查詢的幾種方式

 1  /*  左鏈接 left join 或者 left outer join   */
 2  /* 左鏈接 Table_A表數據所有顯示，Table_B根據條件匹配Table_A 匹配上顯示，不然顯示NULL */
 3  SELECT * from Table_A
 4  SELECT * from Table_B
 5  SELECT * from Table_A a  left outer join Table_B b on a.Code = b.Code
 6  
 7  
 8  
 9  /*  右鏈接 right join 或者 right outer join   */
10  /* 右鏈接 Table_B表數據所有顯示，Table_A根據條件匹配Table_B 匹配上顯示，不然顯示NULL */
11  SELECT * from Table_A
12  SELECT * from Table_B
13  SELECT * from Table_A a right join Table_B b on a.Code = b.Code
14  
15  
16  /*完整外部聯接:full join或full outer join*/
17  /*完整外部聯接返回Table_A和Table_b中的全部行。當Table_A在Table_B表中沒有匹配行時，
18  則Table_B的選擇列表列包含空值。若是表之間有匹配行，則整個結果集行包含基表的數據值。*/
19  SELECT * from Table_A
20  SELECT * from Table_B
21  SELECT * from Table_A a full join Table_B b on a.Code = b.Code
22  
23 /*內鏈接:join或 inner join*/
24 /*返回Table_A和Table_B中匹配的列*/
25  SELECT * from Table_A
26  SELECT * from Table_B
27  SELECT * from Table_A a  join Table_B b on a.Code = b.Code
28  
29  /* 交差鏈接 cross join */
30  /*交差鏈接返回的結果是 Table_A 和Table_B表的笛卡爾積(Table_A的行數乘以Table_B的行數) */
31  SELECT * from Table_A
32  SELECT * from Table_B
33  SELECT Count(*) from Table_A a cross join Table_B 
34  SELECT * from Table_A a cross join Table_B