SQL在軟件測試數據庫中刪除重復記錄

SQL> desc employee

 Name                                      Null?    Type
 ----------------------------------------- -------- ------------------

emp_id                                                NUMBER(10)
emp_name                                           VARCHAR2(20)

salary                                                  NUMBER(10,2)

可以通過(guò)下面的語(yǔ)句查詢(xún)重復的記錄：

SQL> select * from employee;

    EMP_ID EMP_NAME                                  SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         1 sunshine                                      10000

         2 semon                                         20000

         2 semon                                         20000

         3 xyz                                           30000

         2 semon                                         20000


SQL> select distinct * from employee;

    EMP_ID EMP_NAME                                     SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         2 semon                                         20000

         3 xyz                                             30000

SQL>  select * from employee group by emp_id,emp_name,salary having count (*)>1

    EMP_ID EMP_NAME                                     SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         2 semon                                          20000

SQL> select * from employee e1

where rowid in (select max(rowid) from employe e2
 where e1.emp_id=e2.emp_id and

  e1.emp_name=e2.emp_name and e1.salary=e2.salary);

    EMP_ID EMP_NAME                                     SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         3 xyz                                             30000

         2 semon                                         20000

2. 刪除的幾種方法：

（1）通過(guò)建立臨時(shí)表來(lái)實(shí)現

SQL>create table temp_emp as (select distinct * from employee) 

SQL> truncate table employee; (清空employee表的數據）

SQL> insert into employee select * from temp_emp;  (再將臨時(shí)表里的內容插回來(lái)）

 (2）通過(guò)唯一rowid實(shí)現刪除重復記錄.在Oracle中，每一條記錄都有一個(gè)rowid，rowid在整個(gè)數據庫中是唯一的，rowid確定了每條記錄是在Oracle中的哪一個(gè)數據文件、塊、行上。在重復的記錄中，可能所有列的內容都相同，但rowid不會(huì )相同，所以只要確定出重復記錄中那些具有最大或最小rowid的就可以了，其余全部刪除。

SQL>delete from employee e2 where rowid not in (
        select max(e1.rowid) from employee e1 where

        e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and e1.salary=e2.salary);--這里用min(rowid)也可以。

SQL>delete from employee e2 where rowid <(
        select max(e1.rowid) from employee e1 where
        e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and

                  e1.salary=e2.salary);

（3）也是通過(guò)rowid，但效率更高。

SQL>delete from employee where rowid not in (
        select max(t1.rowid) from employee t1 group by

         t1.emp_id,t1.emp_name,t1.salary);--這里用min(rowid)也可以。

    EMP_ID EMP_NAME                                     SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         3 xyz                                             30000

         2 semon                                         20000

SQL> desc employee

 Name                                      Null?    Type
 ----------------------------------------- -------- ------------------

emp_id                                                NUMBER(10)
emp_name                                           VARCHAR2(20)

salary                                                  NUMBER(10,2)

可以通過(guò)下面的語(yǔ)句查詢(xún)重復的記錄：

SQL> select * from employee;

    EMP_ID EMP_NAME                                  SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         1 sunshine                                      10000

         2 semon                                         20000

         2 semon                                         20000

         3 xyz                                           30000

         2 semon                                         20000

SQL> select distinct * from employee;

    EMP_ID EMP_NAME                                     SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         2 semon                                         20000

         3 xyz                                             30000

SQL>  select * from employee group by emp_id,emp_name,salary having count (*)>1

    EMP_ID EMP_NAME                                     SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         2 semon                                          20000

SQL> select * from employee e1

where rowid in (select max(rowid) from employe e2
 where e1.emp_id=e2.emp_id and

  e1.emp_name=e2.emp_name and e1.salary=e2.salary);

    EMP_ID EMP_NAME                                     SALARY

---------- ---------------------------------------- ----------

         1 sunshine                                      10000

         3 xyz                                             30000

         2 semon                                         20000