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;