Maintaining Referential IntegrityPertemuan 2

Matakuliah : T0413/Current Popular IT IITahun : 2007

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AGENDA:•Constraining the Values of Data •Maintaining Referential Integrity •Entering, Deleting, and Changing Data

Book:Mastering SQL by Martin GruberSybex (2000)Chapter : 4 – 6

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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

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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.

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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));

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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);

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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’));

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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 LuckyBarcelonaCHECK (comm < .15 OR city = ‘Barcelona’));

• Dropping constraints:ALTER TABLE Salespeople DROP CONSTRAINT

LuckyBarcelona;

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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

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Maintaining Referential Integrity• Foreign Key and Parent Key• Declaring Columns As Foreign Key:

1. FOREIGN KEY as a table constraintCREATE 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 constraintCREATE 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 valuesCREATE 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 DataThe INSERT statement• Entering values into tables• Syntax:

INSERT INTO table nameVALUES (value,…);

• Example:INSERT INTO SalespeopleVALUES (1001, ‘Peel’, ‘London’, .12);

• Inserting NULLs valueINSERT INTO SalespeopleVALUES (1001, ‘Peel’, NULL, .12);

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Entering, Deleting, and Changing Data (cont’d)

• Naming columns for INSERTINSERT INTO Customers (city, cname, cnum)VALUES (‘London’, ’Hoffman’, 2001);

• Inserting the Result of a QueryINSERT INTO Londonstaff

SELECT * FROM SalespeopleWHERE city = ‘London’;

INSERT INTO LondonstaffSELECT snum, sname, city, comm * 1.1FROM SalespeopleWHERE city = ‘London’;

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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 CustomersSET rating = 200;

• Updating only certain rowsUPDATE Customers

SET rating = 200WHERE snum = 1001;

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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 UPDATEUPDATE Salespeople

SET comm = comm * 2WHERE city = ‘London’;

• Updating to NULL valueUPDATE Customers

SET rating = NULLWhere city = ‘London’;

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End ofMaintaining Referential Integrity

Thank you