Oracle PL/SQL/Constraints/Primary Key
Содержание
Alter to add primary key
<source lang="sql">
SQL> SQL> CREATE TABLE supplier
2 ( supplier_id numeric(10) not null, 3 supplier_name varchar2(50) not null, 4 contact_name varchar2(50) 5 );
Table created. SQL> SQL> desc supplier;
Name Null? Type ----------------------------------------------------------------------------------------------------- -------- -------------------------------------------------------------------- SUPPLIER_ID NOT NULL NUMBER(10) SUPPLIER_NAME NOT NULL VARCHAR2(50) CONTACT_NAME VARCHAR2(50)
SQL> SQL> ALTER TABLE supplier
2 add CONSTRAINT supplier_pk PRIMARY KEY (supplier_id);
Table altered. SQL> SQL> desc supplier;
Name Null? Type ----------------------------------------------------------------------------------------------------- -------- -------------------------------------------------------------------- SUPPLIER_ID NOT NULL NUMBER(10) SUPPLIER_NAME NOT NULL VARCHAR2(50) CONTACT_NAME VARCHAR2(50)
SQL> SQL> drop table supplier; Table dropped. SQL> SQL>
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Create a primary key with more than one field
<source lang="sql">
SQL> -- Create a primary key with more than one field: SQL> SQL> SQL> CREATE TABLE supplier
2 ( supplier_id numeric(10) not null, 3 supplier_name varchar2(50) not null, 4 contact_name varchar2(50), 5 CONSTRAINT supplier_pk PRIMARY KEY (supplier_id, supplier_name) 6 );
Table created. SQL> SQL> desc supplier;
Name Null? Type ----------------------------------------------------------------------------------------------------- -------- -------------------------------------------------------------------- SUPPLIER_ID NOT NULL NUMBER(10) SUPPLIER_NAME NOT NULL VARCHAR2(50) CONTACT_NAME VARCHAR2(50)
SQL> SQL> drop table supplier; Table dropped. SQL> SQL>
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DISTINCT keyword with primary key in select clause
<source lang="sql">
SQL> -- create demo table SQL> create table Employee(
2 ID VARCHAR2(4 BYTE), 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 constraint t_pk primary key(ID) 11 ) 12 /
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"), 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("03","James", "Smith", to_date("19781212","YYYYMMDD"), to_date("19900315","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("04","Celia", "Rice", to_date("19821024","YYYYMMDD"), to_date("19990421","YYYYMMDD"), 2334.78, "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"), 2334.78,"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"), 2334.78,"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"), 2334.78,"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 2334.78 Vancouver Tester 03 James Smith 12-DEC-78 15-MAR-90 2334.78 Vancouver Tester 04 Celia Rice 24-OCT-82 21-APR-99 2334.78 Vancouver Manager 05 Robert Black 15-JAN-84 08-AUG-98 2334.78 Vancouver Tester 06 Linda Green 30-JUL-87 04-JAN-96 2334.78 New York Tester 07 David Larry 31-DEC-90 12-FEB-98 2334.78 New York Manager 08 James Cat 17-SEP-96 15-APR-02 2334.78 Vancouver Tester 8 rows selected. SQL> SQL> SQL> SQL> SQL> SQL> -- DISTINCT keyword with primary key SQL> SQL> SELECT DISTINCT ID FROM Employee; ID
04 08 07 01 02 03 05 06 8 rows selected. SQL> SQL> -- clean the table SQL> drop table Employee
2 /
Table dropped. SQL> SQL>
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Primary Key: A primary key combines a unique and a not null constraint
<source lang="sql">
SQL> --Primary Key: A primary key combines a unique and a not null constraint. SQL> SQL> -- Additionally, a table can have at most one primary key. After creating a primary key, it can be referenced by a foreign key. SQL> SQL> create table myTable (
2 a number primary key, 3 b number 4 );
Table created. SQL> SQL> SQL> insert into myTable values (1,2); 1 row created. SQL> insert into myTable values (2,2); 1 row created. SQL> insert into myTable values (3,2); 1 row created. SQL> insert into myTable values (1,2); insert into myTable values (1,2)
ERROR at line 1: ORA-00001: unique constraint (SYS.SYS_C004362) violated
SQL> SQL> select * from myTable;
A B
----------
1 2
2 2
3 2
SQL> SQL> drop table myTable
2
SQL> / Table dropped. SQL>
</source>
