1 DBS201: More on SQL Lecture 3

2 Agenda Review Constraints Primary Key Not Null Unique Check Foreign Key Changing a Table Definition Changing and deleting Table Rows

3 Review What information is stored in a database structure chart? Data Dictionary shows Column Name Column Type Column Length PK? FK Reference? Req’d? Unique? Validation?

4 Review Terms starting with the largest SQL Terms Native Equivalents Schema/CollectionLibrary TablePhysical File RowRecord ColumnField ViewLogical File IndexLogical File

5 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.

6 Review Is different than

7 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

8 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

9 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.

10 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.

11 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?

12 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 and 40000)  (Grade IN(‘A’,’B’,’C’,’D’,’F’,’I’))

13 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 AND 4000),  CONSTRAINT TEST_GRADE_CK  CHECK (GRADE IN('A', 'B', 'C', 'D', 'F', 'I') ) )

14 Constraints – Foreign Key FOREIGN KEY The 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.

15 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 ) )

16 Foreign Key Constraint INSERT INTO PAINTRUS/CUSTOMER VALUES('99999', 'Smith', 'Ronald', 'Mississauga', , '111') Operation not allowed by referential constraint CUSTOMER_CUSTOMER_CP INSERT INTO PAINTRUS/painter VALUES('111', 'Wong', 'Mary','Mississauga', ) 1 rows inserted in PAINTER in PAINTRUS. INSERT INTO PAINTRUS/CUSTOMER VALUES('99999', 'Smith', 'Ronald', 'Mississauga', , '111') 1 rows inserted in CUSTOMER in PAINTRUS.

17 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

18 Constraints - Examples  LAB 3 has examples of these 5 types of constraints.

19 Agenda Data Definition Language How to use SQL to update table definitions Data Manipulation Language How to update data in a table How to delete rows of data in a table

20 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

21 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)

22 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'

23 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

24 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‘)

25 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)

26 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’

27 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’

28 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