这不是外链接。
外连接:
LEFT OUTER JOIN 或 LEFT JOINRIGHT OUTER JOIN 或 RIGHT JOINFULL OUTER JOIN 或 FULL JOIN
--使用左外链接
USE pubs
SELECT a.au_fname, a.au_lname, p.pub_name
FROM authors a LEFT OUTER JOIN publishers p
ON a.city = p.city
ORDER BY p.pub_name ASC, a.au_lname ASC, a.au_fname ASC
--
外连接:
LEFT OUTER JOIN 或 LEFT JOINRIGHT OUTER JOIN 或 RIGHT JOINFULL OUTER JOIN 或 FULL JOIN
--使用左外链接
USE pubs
SELECT a.au_fname, a.au_lname, p.pub_name
FROM authors a LEFT OUTER JOIN publishers p
ON a.city = p.city
ORDER BY p.pub_name ASC, a.au_lname ASC, a.au_fname ASC
--
---這個不是外连接!他是等值查询,这个相当于inner join:
select Card_Kind from T_Client_Info a inner join T_OpenCard_Info b on a.Client_Code=b.Client_Code
select select_list from table1,table2,table3 wherer table1.column1=table2.column1 and
table1.column2=ttable3.column2 and condition [(select Card_Kind from T_Client_Info a,T_OpenCard_Info b where a.Client_Code=b.Client_Code ) as Card_Kind,]这个语句放在检索语句,只是嵌套查询的一种写法。外连接包括左外连接,右外连接,全外连接三种基本语法:
左外连接:
select select_list from table1 left join table2 on table1.column1=table2.column2右外连接:select select_list from table1 right join table2 on table1.column1=table2.column2全外连接:select select_list from table1 full table2 on table1.column1=table2.column2