в 13:45, 26 мая 2010

2010-05-26T13:45:19Z

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2010-05-26T10:01:57Z

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==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>

</source>

==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>

</source>

==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>

</source>

==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>

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в 13:45, 26 мая 2010

Admin: 1 версия