Question

创建视图时，如何从一个表中选择所有内容，从另一个表中选择某些列，

例如我写过

CREATE VIEW NOT_IN_MAN_GLA_LND
AS 
     SELECT 
         E.EMPLOYEE_ID, E.TITLE, E.FIRST_NAME, E.LAST_NAME, 
         E.HOUSE_NO, E.ADDRESS, E.POSTCODE, E.TELE_NO, E.START_DATE, 
         P.CITY, P.POST_CODE
     FROM 
         EMPLOYEE E, POSTCODE P
     WHERE 
         E.POSTCODE = P.POSTCODE
         AND P.CITY NOT IN ('MAN', 'GLA', 'LND');

因此，除了写出employee表中的所有列之外，我可以只选择它们，而仍然只选择邮政编码表中的两列。

Answer 1

更好的答案是使用正确的，明确的，标准 JOIN语法：

CREATE VIEW NOT_IN_MAN_GLA_LND AS
    SELECT E.*, P.CITY, P.POST_CODE
    FROM EMPLOYEE E JOIN
         POSTCODE P
         ON E.POSTCODE = P.POSTCODE
    WHERE P.CITY NOT IN ('MAN', 'GLA', 'LND');

如果您想在结果中包括员工-甚至没有匹配邮政编码的员工-那么：

CREATE VIEW NOT_IN_MAN_GLA_LND AS
    SELECT E.*, P.CITY, P.POST_CODE
    FROM EMPLOYEE E LEFT JOIN
         POSTCODE P
         ON E.POSTCODE = P.POSTCODE
    WHERE P.CITY NOT IN ('MAN', 'GLA', 'LND') OR
          P.CITY IS NULL;

Answer 2

create or replace VIEW NOT_IN_MAN_GLA_LND
AS SELECT E.*, P.CITY, P.POST_CODE as P_POST_CODE

FROM EMPLOYEE E, POSTCODE P

WHERE E.POSTCODE = P.POSTCODE

AND P.CITY NOT IN ('MAN', 'GLA', 'LND');

for example dept nd emp table:

create or replace view ns_1_v as
select e.*,d.deptno as d_dname,d.dname 
from scott.emp e ,scott.dept d
where
e.deptno=d.deptno;

如果两个表中都有一个通用名称，则必须为列名称提供别名，否则，在您的情况下，dupllicaate column name error会抛出postcode，因此请为其别名

从一个表中选择所有内容，从另一个SQL中选择某些列

2 个答案: