Question

我有一个名为Student的表，列名为uniquename，age，department，city，Homecountry和另一个名为Employee的表，列为uniquename，exp，qualification，Homecountry。

现在我想用where条件Student.uniquename = Employee.uniquename和Student.Homecountry = Employee.Homecountry下的Employee表的资格栏值更新Student表的department列。

请帮我写一下更新声明。

Answer 1

这种查询称为相关子查询。根据您的要求，查询将如下....

update students s
  set s.department = (
          select e.qualification
            from employee e
            where s.uniquename = e.uniquename 
              and s.Homecountry = e.Homecountry
       );

根据您的回复更新此信息。

再次，继续前进，始终发布创建表并插入语句（以及预期结果）以重现您的案例。如果您没有看到预期的结果，或者在执行查询时看到错误，请发布确切的消息，而不是仅仅说“不工作”。这是我的sqlplus会话的结果。

---创建表和插入语句

create table student(
     name varchar2(20),
     age  number,
     department varchar2(3),
     HomeCountry varchar2(10)
    );

Table created.

create table employee5(
     name varchar2(20),
     exp  number,
     qualification varchar2(3),
     homecountry varchar2(10)
   );

Table created.

insert into student values ('Mohan',25,'EEE','India');
insert into student values ('Raja',27,'EEE','India');
insert into student values ('Ahamed',26,'ECE','UK');
insert into student values ('Gokul',25,'IT','USA');
commit;

insert into employee5 values ('Mohan',25,'ECE','India');
insert into employee5 values ('Raja',24,'IT','India');
insert into employee5 values ('Palani',26,'ECE','USA');
insert into employee5 values ('Sathesh',29,'CSE','CANADA');
insert into employee5 values ('Ahamed',28,'ECE','UK');
insert into employee5 values ('Gokul',29,'EEE','USA');
commit;

在更新数据之前......

SQL> select * from student;

NAME                        AGE DEP HOMECOUNTR
-------------------- ---------- --- ----------
Mohan                        25 EEE India
Raja                         27 EEE India
Ahamed                       26 ECE UK
Gokul                        25 IT  USA

SQL> select * from employee5;

NAME                        EXP QUA HOMECOUNTR
-------------------- ---------- --- ----------
Mohan                        25 ECE India
Raja                         24 IT  India
Palani                       26 ECE USA
Sathesh                      29 CSE CANADA
Ahamed                       28 ECE UK
Gokul                        29 EEE USA

更新声明和结果

  1  update student s set s.age =
  2     ( select e.exp
  3          from employee5 e
  4          where e.name = s.name
  5            and e.homecountry = s.homecountry
  6*    )
SQL> /

4 rows updated.

SQL> select * from student;

NAME                        AGE DEP HOMECOUNTR
-------------------- ---------- --- ----------
Mohan                        25 EEE India
Raja                         24 EEE India
Ahamed                       28 ECE UK
Gokul                        29 IT  USA

SQL> commit;

Commit complete.

Answer 2

update student s 
   set s.age = (select e.exp 
                  from employee5 e 
                  where e.name = s.name 
                    and e.homecountry = s.homecountry  
                    and rownum < 2
               )
where s.age in (select age from employee5)

它不会显示消息子查询返回多个记录

如何使用另一个表的列值更新一个表列值？

2 个答案: