Oracle PL/SQL/Constraints/Drop Constraint
Alter table to drop constraint with name
<source lang="sql">
SQL> --Unique Key SQL> SQL> SQL> create table myTable (
2 a number unique, 3 b number 4 );
Table created. SQL> SQL> SQL> desc Usage: DESCRIBE [schema.]object[@db_link] SQL> SQL> insert into myTable values (4, 5); 1 row created. SQL> insert into myTable values (2, 1); 1 row created. SQL> insert into myTable values (2, 1); insert into myTable values (2, 1)
ERROR at line 1: ORA-00001: unique constraint (SYS.SYS_C004357) violated
SQL> insert into myTable values (9, 8); 1 row created. SQL> insert into myTable values (6, 9); 1 row created. SQL> insert into myTable values (null,9); 1 row created. SQL> insert into myTable values (null,9); 1 row created. SQL> SQL> select * from myTable;
A B
----------
4 5
2 1
9 8
6 9
9
9
6 rows selected. SQL> SQL> alter table myTable drop constraint sys_c004357; Table altered. SQL> SQL> SQL> insert into myTable values (4, 5); 1 row created. SQL> insert into myTable values (2, 1); 1 row created. SQL> insert into myTable values (2, 1); 1 row created. SQL> insert into myTable values (9, 8); 1 row created. SQL> insert into myTable values (6, 9); 1 row created. SQL> insert into myTable values (null,9); 1 row created. SQL> insert into myTable values (null,9); 1 row created. SQL> SQL> select * from myTable;
A B
----------
4 5
2 1
9 8
6 9
9
9
4 5
2 1
2 1
9 8
6 9
A B
----------
9
9
13 rows selected. SQL> SQL> drop table myTable;
</source>
Drop a UNIQUE constraint without specifying its name by referencing the column or columns
<source lang="sql">
SQL> -- create demo table SQL> create table Employee(
2 ID VARCHAR2(4 BYTE) unique, 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> -- Drop a UNIQUE constraint without specifying its name by referencing the column or columns. SQL> SQL> ALTER TABLE Employee DROP UNIQUE (id); Table altered. SQL> SQL> SQL> SQL> -- clean the table SQL> drop table Employee
2 /
Table dropped. SQL> SQL> SQL>
</source>
Drop Unique Constraint and Add Primary Key
<source lang="sql">
SQL> SQL> CREATE TABLE myTable (
2 Name VARCHAR(50) NOT NULL, 3 PhoneNo VARCHAR(15), 4 CONSTRAINT unq_name UNIQUE(Name));
Table created. SQL> SQL> ALTER TABLE myTable DROP CONSTRAINT unq_name; Table altered. SQL> ALTER TABLE myTable ADD CONSTRAINT PK_myTableName PRIMARY KEY (Name); Table altered. SQL> SQL> SQL> drop table myTable; Table dropped.
</source>
