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DBS201: More on SQL

Lecture 3

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Agenda

Review Constraints

Primary KeyNot NullUniqueCheckForeign Key

Changing a Table Definition Changing and deleting Table Rows

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Review

What information is stored in a database structure chart?

Data Dictionary showsColumn NameColumn TypeColumn LengthPK?FK Reference?Req’d?Unique?Validation?

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Review

Terms starting with the largest SQL Terms Native Equivalents

Schema/Collection Library Table Physical File Row Record Column Field View Logical File Index Logical File

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Review

CREATE TABLE painter ( p_num char (4) not null with default, p_lname char (15) not null with default, p_fname char (15) not null with default, p_city char (20), p_phone dec (10), Constraint Painter_P_num_PK primary key (p_num) ) Table PAINTER in DR201C40 created but was not journaled.

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Review

Is different than

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Review

CREATE TABLE painter ( p_num char (4) not null with default, p_lname char (15) not null with default, p_fname char (15) not null with default, p_city char (20), p_phone dec (10), Constraint Painter_P_num_PK primary key (p_num) ) Table PAINTER created in PAINTRUS

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Constraints

Constraints are used to ensure that the database receives “good” data

PRIMARY KEY unique and not null. NOT NULL a value must exist. UNIQUE value exists only once in a column. CHECK value must pass validation criteria FOREIGN KEY used to enforce Relational Integrity between two tables

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Constraints – Primary Key

PRIMARY KEY Provides rapid access to a row on a table

Guarantees uniqueness of the PK field (there can be only one Doctor # D5524 in Ontario)

Insists that a primary key value be specified by the user for every row on the table.

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Constraints – Not Null

NOT NULL The user must specify a value.

NOT NULL WITH DEFAULT The user must specify a value or the system will

specify a value.(spaces for char, 0 for numeric and “sysdate” for date fields)

NOT NULL WITH DEFAULT “value” The user must specify a value or the system will

insert “value” into the field.

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Constraints – Unique

UNIQUE The database will not allow rows to be added or

modified if it results in the unique field occurring more than once in the column in a table.

This is useful for fields like: Social Insurance Number Driver’s License Number Ontario Health Card Number Why not make these a primary key to uniquely locate a

table row? Do you want someone in your company having any of these

unique numbers when they need to update your address?

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Constraints – Check

CHECK The database will examine the value of the

field. There is a condition to be satisfied. The database will not allow rows to be added or modified if it results in the field failing the validation.

Here are some common validations: (Age >= 18 and Age <= 49) (Salary BETWEEN 20000 and 40000) (Grade IN(‘A’,’B’,’C’,’D’,’F’,’I’))

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Constraints – Check

CREATE TABLE TEST ( AGE DECIMAL (3,0) NOT NULL, SALARY DECIMAL (7,2) NOT NULL WITH DEFAULT, GRADE CHARACTER (1), CONSTRAINT TEST_AGE_CK CHECK (AGE >= 18 AND AGE <= 49), CONSTRAINT TEST_SALARY_CK CHECK (SALARY BETWEEN 20000 AND 4000), CONSTRAINT TEST_GRADE_CK CHECK (GRADE IN('A', 'B', 'C', 'D', 'F', 'I') ) )

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Constraints – Foreign Key

FOREIGN KEYThe Foreign Key is used to get information from

another table using the Primary Key of the other table.

A PATIENT record has the DoctorNum as a Foreign Key field. DoctorNum is the Primary Key of the DOCTOR table. The DoctorNum is used to get information about the Doctor from the DOCTOR table.

The Foreign Key is used to enforce relational integrity between the two tables. We will have more to say about Relational Integrity later in this course.

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Constraints - Examples CREATE TABLE customer( c_num char (5) not null with default, c_lname char (15) not null with default, c_fname char (15) not null with default, c_city char (20), c_phone dec (10), cp_num char(4), Constraint Customer_c_num_PK primary key (c_num), Constraint Customer_Customer_cp_num_FK Foreign Key (cp_num) References paintrus.Painter (p_num ) )

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Foreign Key Constraint

INSERT INTO PAINTRUS/CUSTOMER VALUES('99999', 'Smith', 'Ronald',

'Mississauga', 9059998888, '111') Operation not allowed by referential constraint

CUSTOMER_CUSTOMER_CP INSERT INTO PAINTRUS/painter VALUES('111', 'Wong',

'Mary','Mississauga', 9054443234) 1 rows inserted in PAINTER in PAINTRUS. INSERT INTO PAINTRUS/CUSTOMER

VALUES('99999', 'Smith', 'Ronald', 'Mississauga', 9059998888, '111')

1 rows inserted in CUSTOMER in PAINTRUS.

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Foreign Key Constraint

delete from painter Delete prevented by referential constraint

CUSTOMER_CUSTOMER_CP_NUM delete from customer 1 rows deleted from CUSTOMER in PAINTRUS. delete from painter 1 rows deleted from PAINTER in PAINTRUS

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Constraints - Examples

LAB 3 has examples of these 5 types of constraints.

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Agenda

Data Definition LanguageHow to use SQL to update table

definitions

Data Manipulation LanguageHow to update data in a tableHow to delete rows of data in a table

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Changing a Table Definition

ALTER TABLE Used to update a database definition

Syntax ALTER TABLE tablename

Can do any of the following Add a field Alter a field Drop a field Add a constraint Drop a constraint

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Changing a Table Definition

To add a field: ALTER TABLE tablename ADD COLUMN field-name datatype Example: ALTER TABLE MARINA

ADD COLUMN Boat_Description CHAR (20)

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Changing a Table Definition

To change a field definition: ALTER TABLE tablename ALTER COLUMN fieldname SET DATA TYPE data type Example: ALTER TABLE MARINA

ALTER COLUMN Boat_Description SET DATA TYPE CHAR(12) NOT NULL WITH DEFAULT 'abc'

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Changing a Table Definition

To remove a field: ALTER TABLE tablename DROP COLUMN column_name Example: ALTER TABLE MARINA DROP COLUMN Boat_Description *Note – be careful not to drop a column that you may in fact need as

the data will be lost.

Rule of thumb: do not alter a table after it contains data

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Changing a Table Definition

To add a constraint: Example defining the PRIMARY KEY:

ALTER TABLE MARINA ADD CONSTRAINT Marina_Boat_No_PK PRIMARY KEY (Boat_No) Example of adding a check constraint:

ALTER TABLE MARINA ADD CONSTRAINT Marina_Boat_Code_CK CHECK (Boat_Code BETWEEN 'AAA' AND 'DDD‘)

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Updating a Table Definition - DDL

To drop a constraint ALTER TABLE tablename DROP CONSTRAINT constraint_name ALTER TABLE MARINA DROP CONSTRAINT Boat_Name_UN

Name must be the name assigned to the constraint (may have been assigned by user or by system)

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Updating Data in a Table

To update data in a table, use UPDATE. UPDATE tablename SET column name = new value WHERE condition examples UPDATE MARINA SET Dock_Number = ‘AAA' UPDATE MARINA SET Dock_Number = ‘AAB‘ WHERE Marina_Num = ‘M-2407’

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How to Delete Rows in Tables-DML

To delete a row in a table, Use the Delete statement

DELETE FROM tablename

WHERE condition

example

DELETE FROM MARINA

WHERE Dock_Num = ‘CCC’

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Updating a Table Definition - DDL

Adding a Primayr Key and Foreign Key Constraint ALTER TABLE CUSTOMER

ADD CONSTRAINT CUSTOMER_CUSTOMER_NUMBER_PK PRIMARY KEY (CUSTOMER_NUMBER)

ALTER TABLE CUSTOMER ADD CONSTRAINT CUSTOMER_SALES_REP_NUMBER_FK FOREIGN KEY (SALES_REP_NUMBER) REFERENCES SALESREP(SALES_REP_NUMBER)

Table SALESREP in PRMIERC40 does not have a matching parent key