Matakuliah : T0413/Current Popular IT II
Tahun
: 2007
Maintaining Referential Integrity
Pertemuan 2
AGENDA:
•Constraining the Values of Data
•Maintaining Referential Integrity
•Entering, Deleting, and Changing Data
Book:
Mastering SQL by Martin Gruber
Sybex (2000)
Chapter : 4 – 6
2
Constraining the Values of Data
• Declaring constraints
– Values that can be entered into its columns on a table
– SQL will generally reject any values that violate the criteria you created
before
• Syntax:
CREATE TABLE tablename
({columnname datatype column constraint} …,
[table constraint (columnname ,…) ,…];
• Alternative : ALTER TABLE
3
Constraining the Values of Data (cont’d)
• Using Constraints to Exclude NULLs
– To prevent a column from permitting NULLs as a value
– Use CREATE TABLE statement with NOT NULLs constraint
• Example:
CREATE TABLE Salespeople
(snum INTEGER NOT NULL,
sname CHAR(10) NOT NULL,
city CHAR(10),
comm DECIMAL);
• Column with NOT NULL constraint must be assigned values in every
INSERT clause.
4
Constraining the Values of Data (cont’d)
• Specifying the Primary Key
• Example:
CREATE TABLE Salespeople
(snum INTEGER NOT NULL PRIMARY KEY,
sname CHAR(10) NOT NULL,
city CHAR(10),
comm DECIMAL);
• Primary Keys of More Than One Column
• Example:
CREATE TABLE Namefield
(firstname CHAR(10) NOT NULL,
lastname CHAR(10) NOT NULL,
city CHAR(10),
PRIMARY KEY (firstname, lastname));
5
Constraining the Values of Data (cont’d)
• Making Sure Values Are Unique
– Using UNIQUE constraint
– UNIQUE vs. PRIMARY KEY:
• PRIMARY KEY constraint can only be used on one column or group of columns.
UNIQUE constraint may be used any number of times.
• PRIMARY KEY column may not contain NULLs, UNIQUE constraint may.
– Example:
CREATE TABLE Salespeople
(snum INTEGER NOT NULL PRIMARY KEY,
sname CHAR(10) NOT NULL UNIQUE,
city CHAR(10),
comm DECIMAL);
6
Constraining the Values of Data (cont’d)
• Checking Column Values
– Using CHECK to Predetermine Valid Input Values
– Example:
CREATE TABLE Salespeople
(snum INTEGER NOT NULL PRIMARY KEY,
sname CHAR(10) NOT NULL,
city CHAR(10) CHECK,
(city IN (‘London’, ‘New York’, ‘San Jose’, ‘Barcelona’)),
comm DECIMAL CHECK (comm < 1));
– Check Conditions Based on Multiple Columns
– Example:
CREATE TABLE Salespeople
(snum INTEGER NOT NULL PRIMARY KEY,
sname CHAR(10) NOT NULL UNIQUE,
city CHAR(10),
comm DECIMAL,
CHECK (comm < .15 OR city = ‘Barcelona’));
7
Constraining the Values of Data (cont’d)
• Naming and Dropping Constraints
• Example:
CREATE TABLE Salespeople
(snum INTEGER NOT NULL PRIMARY KEY,
sname CHAR(10) NOT NULL UNIQUE,
city CHAR(10),
comm DECIMAL,
CONSTRAINT LuckyBarcelona
CHECK (comm < .15 OR city = ‘Barcelona’));
• Dropping constraints:
ALTER TABLE Salespeople DROP CONSTRAINT LuckyBarcelona;
8
Constraining the Values of Data (cont’d)
• Assigning Default Values
• Example:
CREATE TABLE Salespeople
(snum INTEGER NOT NULL PRIMARY KEY,
sname CHAR(10) NOT NULL,
city CHAR(10) DEFAULT = ‘New York’,
comm DECIMAL CHECK (comm < 1));
• Default Values and NULLs
9
Maintaining Referential Integrity
•
•
Foreign Key and Parent Key
Declaring Columns As Foreign Key:
1. FOREIGN KEY as a table constraint
CREATE TABLE Customers
(cnum INTEGER NOT NULL PRIMARY KEY,
cname CHAR(10),
city CHAR(10),
snum INTEGER,
FOREIGN KEY (snum) REFERENCES Salespeople(snum));
Note: Customers table with snum defined as a foreign key referencing the
Salespeople table.
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Maintaining Referential Integrity (cont’d)
2. FOREIGN KEY as a column constraint
CREATE TABLE Customers
(cnum INTEGER NOT NULL PRIMARY KEY,
cname CHAR(10),
city CHAR(10),
snum INTEGER REFERENCES Salespeople(snum));
Note: Customers table with snum as a foreign key whose parent key is
Salespeople.snum.
It is equivalent to this table constraint:
FOREIGN KEY (snum) REFERENCES Salespeople (snum)
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Maintaining Referential Integrity (cont’d)
3. Using FOREIGN KEY to predetermined valid input values
CREATE TABLE Officecities
(office (CHAR(10) NOT NULL PRIMARY KEY);
CREATE TABLE Salespeople
( snum INTEGER NOT NULL PRIMARY KEY,
sname CHAR(10) NOT NULL,
city CHAR(10) REFERENCES Officecities,
comm DECIMAL CHECK (comm < 1));
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Maintaining Referential Integrity (cont’d)
• PRIMARY vs. UNIQUE Parent Keys
• Multicolumn Foreign Keys
• Referential Triggered Actions :
– how parent-key changes affect foreign keys
– It enable you to specify when creating a FOREIGN KEY constraint what you
would like to have happen to the foreign-key values when the referenced
parent-key values are deleted or changed.
– UPDATE : what happens to a foreign key value when the parent key value it
references is changed.
– DELETE : what happens to a foreign key value when the parent key row it
references is deleted.
– Solutions : CASCADE, SET NULL, SET DEFAULT, NO ACTION
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Entering, Deleting, and Changing Data
The INSERT statement
• Entering values into tables
• Syntax:
INSERT INTO table name
VALUES (value,…);
• Example:
INSERT INTO Salespeople
VALUES (1001, ‘Peel’, ‘London’, .12);
• Inserting NULLs value
INSERT INTO Salespeople
VALUES (1001, ‘Peel’, NULL, .12);
14
Entering, Deleting, and Changing Data (cont’d)
• Naming columns for INSERT
INSERT INTO Customers (city, cname, cnum)
VALUES (‘London’, ’Hoffman’, 2001);
• Inserting the Result of a Query
INSERT INTO Londonstaff
SELECT * FROM Salespeople
WHERE city = ‘London’;
INSERT INTO Londonstaff
SELECT snum, sname, city, comm * 1.1
FROM Salespeople
WHERE city = ‘London’;
15
Entering, Deleting, and Changing Data (cont’d)
The DELETE statement
• Removing Rows from tables
• DELETE FROM Salespeople;
• DELETE FROM Salespeople WHERE snum = 1003;
• DELETE FROM Salespeople WHERE city = ‘London’;
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Entering, Deleting, and Changing Data (cont’d)
The UPDATE Statement
• Changing field values
• Example:
UPDATE Customers
SET rating = 200;
• Updating only certain rows
UPDATE Customers
SET rating = 200
WHERE snum = 1001;
17
Entering, Deleting, and Changing Data (cont’d)
• Updating multiple columns at once
UPDATE Salespeople
SET sname = ‘Gibson’, city = ‘Boston’, comm = .10
WHERE snum = 1004;
• Using value expression in UPDATE
UPDATE Salespeople
SET comm = comm * 2
WHERE city = ‘London’;
• Updating to NULL value
UPDATE Customers
SET rating = NULL
Where city = ‘London’;
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End of
Maintaining Referential Integrity
Thank you
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