Oracle PL/SQL/Table/Drop Columns
Alter table to Drop a column
SQL> -- create demo table
SQL> create table Employee(
2 ID VARCHAR2(4 BYTE) NOT NULL,
3 First_Name VARCHAR2(10 BYTE),
4 Last_Name VARCHAR2(10 BYTE),
5 Start_Date DATE,
6 End_Date DATE,
7 Salary Number(8,2),
8 City VARCHAR2(10 BYTE),
9 Description VARCHAR2(15 BYTE)
10 )
11 /
Table created.
SQL>
SQL> -- prepare data
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date, End_Date, Salary, City, Description)
2 values ("01","Jason", "Martin", to_date("19960725","YYYYMMDD"), to_date("20060725","YYYYMMDD"), 1234.56, "Toronto", "Programmer")
3 /
1 row created.
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date, End_Date, Salary, City, Description)
2 values("02","Alison", "Mathews", to_date("19760321","YYYYMMDD"), to_date("19860221","YYYYMMDD"), 6661.78, "Vancouver","Tester")
3 /
1 row created.
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date, End_Date, Salary, City, Description)
2 values("03","James", "Smith", to_date("19781212","YYYYMMDD"), to_date("19900315","YYYYMMDD"), 6544.78, "Vancouver","Tester")
3 /
1 row created.
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date, End_Date, Salary, City, Description)
2 values("04","Celia", "Rice", to_date("19821024","YYYYMMDD"), to_date("19990421","YYYYMMDD"), 2344.78, "Vancouver","Manager")
3 /
1 row created.
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date, End_Date, Salary, City, Description)
2 values("05","Robert", "Black", to_date("19840115","YYYYMMDD"), to_date("19980808","YYYYMMDD"), 2334.78, "Vancouver","Tester")
3 /
1 row created.
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date, End_Date, Salary, City, Description)
2 values("06","Linda", "Green", to_date("19870730","YYYYMMDD"), to_date("19960104","YYYYMMDD"), 4322.78,"New York", "Tester")
3 /
1 row created.
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date, End_Date, Salary, City, Description)
2 values("07","David", "Larry", to_date("19901231","YYYYMMDD"), to_date("19980212","YYYYMMDD"), 7897.78,"New York", "Manager")
3 /
1 row created.
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date, End_Date, Salary, City, Description)
2 values("08","James", "Cat", to_date("19960917","YYYYMMDD"), to_date("20020415","YYYYMMDD"), 1232.78,"Vancouver", "Tester")
3 /
1 row created.
SQL>
SQL>
SQL>
SQL> -- display data in the table
SQL> select * from Employee
2 /
ID FIRST_NAME LAST_NAME START_DAT END_DATE SALARY CITY DESCRIPTION
---- ---------- ---------- --------- --------- ---------- ---------- ---------------
01 Jason Martin 25-JUL-96 25-JUL-06 1234.56 Toronto Programmer
02 Alison Mathews 21-MAR-76 21-FEB-86 6661.78 Vancouver Tester
03 James Smith 12-DEC-78 15-MAR-90 6544.78 Vancouver Tester
04 Celia Rice 24-OCT-82 21-APR-99 2344.78 Vancouver Manager
05 Robert Black 15-JAN-84 08-AUG-98 2334.78 Vancouver Tester
06 Linda Green 30-JUL-87 04-JAN-96 4322.78 New York Tester
07 David Larry 31-DEC-90 12-FEB-98 7897.78 New York Manager
08 James Cat 17-SEP-96 15-APR-02 1232.78 Vancouver Tester
8 rows selected.
SQL>
SQL>
SQL>
SQL> Alter table Employee Drop column Description;
Table altered.
SQL>
SQL>
SQL> select * from employee;
ID FIRST_NAME LAST_NAME START_DAT END_DATE SALARY CITY
---- ---------- ---------- --------- --------- ---------- ----------
01 Jason Martin 25-JUL-96 25-JUL-06 1234.56 Toronto
02 Alison Mathews 21-MAR-76 21-FEB-86 6661.78 Vancouver
03 James Smith 12-DEC-78 15-MAR-90 6544.78 Vancouver
04 Celia Rice 24-OCT-82 21-APR-99 2344.78 Vancouver
05 Robert Black 15-JAN-84 08-AUG-98 2334.78 Vancouver
06 Linda Green 30-JUL-87 04-JAN-96 4322.78 New York
07 David Larry 31-DEC-90 12-FEB-98 7897.78 New York
08 James Cat 17-SEP-96 15-APR-02 1232.78 Vancouver
8 rows selected.
SQL>
SQL>
SQL>
SQL>
SQL> -- clean the table
SQL> drop table Employee
2 /
Table dropped.
SQL>
SQL>
Drop a column
SQL>
SQL> CREATE TABLE myTable (
2 Name VARCHAR(50) PRIMARY KEY NOT NULL,
3 PhoneNo VARCHAR(15) DEFAULT "Unknown Phone",
4 SSN VARCHAR(15) NOT NULL,
5 CHECK (SSN LIKE "[0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]"));
Table created.
SQL>
SQL>
SQL>
SQL> ALTER TABLE myTable DROP COLUMN PhoneNo;
Table altered.
SQL>
SQL> drop table myTable;
Table dropped.
SQL>
Dropping Columns and query user_unused_col_tabs
create table people(
employee_id number(9),
first_name varchar2(15),
last_name varchar2(20),
email varchar2(25),
constraint pk_people primary key (employee_id)
);
insert into people values (1, "Tom", "Kyte", "YourName@q.ru");
insert into people values (2, "Sean", "Viper", "sdillon@q.ru");
insert into people values (3, "Christopher", "Beck", "clbeck@q.ru");
alter table people
drop column first_name
/
alter table people
drop column last_name
/
select * from user_unused_col_tabs;
ALTER TABLE departments DROP UNUSED COLUMNS;
drop table people;