1. Chapter 8 Embedded SQL

2. Objectives Embed SQL commands in PL/SQL programs
Retrieve single rows using embedded SQL
Update a table using embedded INSERT, UPDATE, and DELETE commands
Use cursors to retrieve multiple rows in embedded SQL

3. Objectives Update a database using cursors
Manage errors in programs containing embedded SQL commands
Use SQL in a language that does not support embedded SQL commands

4. Introduction SQL is a non-procedural language
Non-procedural language: many tasks can be accomplished using a single, relatively simple command
Procedural language: computer must be given the step-by-step process for accomplishing tasks

5. Introduction
PL/SQL
procedural language developed by Oracle
an extension of SQL
This chapter uses PL/SQL to illustrate how to embed SQL commands in another language
To embed SQL commands means to include SQL commands directly within programs written in another language

6. Using Prompt Variables
There are many sources of input for SQL commands
In this text, input comes from prompt variables
Prompt variables: variables for which the user is prompted to enter a value
To designate a prompt variable, precede the name with an ampersand (&)

7. Using Prompt Variables
Problem:
List the last name of the sales rep whose number is contained in the prompt variable I_REP_NUM.
Solution:
SQL> SELECT LAST_NAME 2 FROM REP 3 WHERE REP_NUM = '&I_REP_NUM';

8. PL/SQL Programs SQL commands can be embedded in PL/SQL programs
The programs can be created and saved as script files
To run the programs, run the script files

9. Retrieving a Single Row and Column
Problem:
Write a PL/SQL program to obtain the last name of the sales rep whose number is contained in the prompt variable I_REP_NUM, place it in the variable I_LAST_NAME, and then display the contents of I_LAST_NAME.

10. Retrieving a Single Row and Column
To place the results of a command in a variable, use the INTO clause
To see the contents of the line (the output), use:
SET SERVEROUTPUT ON

11. Retrieving a Single Row and Column
Solution:
SET SERVEROUTPUT ON DECLARE I_REP_NUM CHAR(2); I_LAST_NAME CHAR(15); BEGIN SELECT LAST_NAME INTO I_LAST_NAME FROM REP WHERE REP_NUM = '&I_REP_NUM'; DBMS_OUTPUT.PUT_LINE(I_LAST_NAME); END; /

12. Using the %Type Attribute
%TYPE attribute: ensures that a variable has the same type as a particular column
To assign the variable I_REP_NUM the same type as the REP_NUM column in the REP table, use the following: 
I_REP_NUM REP.REP_NUM%TYPE

13. Retrieving a Single Row from a Join
An embedded SQL command can be used to join tables
Problem:
Obtain the name of the customer whose customer number is stored in the prompt variable I_CUSTOMER_NUM, and the last and first names of the sales rep who represents this customer.

14. Retrieving a Single Row from a Join
SET SERVEROUTPUT ON DECLARE I_LAST_NAME REP.LAST_NAME%TYPE; I_FIRST_NAME REP.FIRST_NAME%TYPE; I_CUSTOMER_NUM CUSTOMER.CUSTOMER_NUM%TYPE; I_CUSTOMER_NAME CUSTOMER.CUSTOMER_NAME%TYPE; BEGIN SELECT LAST_NAME, FIRST_NAME, CUSTOMER_NAME INTO I_LAST_NAME, I_FIRST_NAME, I_CUSTOMER_NAME FROM REP, CUSTOMER WHERE REP.REP_NUM = CUSTOMER.REP_NUM AND CUSTOMER_NUM = '&I_CUSTOMER_NUM'; DBMS_OUTPUT.PUT_LINE(I_CUSTOMER_NAME); DBMS_OUTPUT.PUT_LINE(I_LAST_NAME); DBMS_OUTPUT.PUT_LINE(I_FIRST_NAME) END; /

15. Inserting a Row into a Table
To update databases from within PL/SQL programs, appropriate SQL commands are used
SQL INSERT: add a row to a table in the database
Problem:
Add a row to the REP table. Use prompt variables to obtain values for the fields.

16. Inserting a Row into a Table
The procedural code part of the solution program is:
BEGIN INSERT INTO REP (REP_NUM, LAST_NAME, FIRST_NAME, STREET, CITY, STATE, ZIP, COMMISSION, RATE) VALUES ('&I_REP_NUM', '&I_LAST_NAME', '&I_FIRST_NAME', '&I_STREET', '&I_CITY', '&I_STATE', '&I_ZIP', &I_COMMISSION, &I_RATE); END;

17. Changing a Single Row in a Table
SQL commands can also be used to update the rows in a database
Problem:
Change the last name of the sales rep whose number is stored in I_REP_NUM to the value currently stored in I_LAST_NAME.

18. Changing a Single Row in a Table
Solution:
SET SERVEROUTPUT ON DECLARE I_REP_NUM REP.REP_NUM%TYPE; I_LAST_NAME REP.LAST_NAME%TYPE;   BEGIN UPDATE REP SET LAST_NAME = '&I_LAST_NAME‘ WHERE REP_NUM = '&I_REP_NUM'; END; /

19. Deleting Rows from a Table
SQL commands can be used to delete rows
Problem:
Delete the sales rep whose number currently is stored in I_REP_NUM from the REP table.

20. Deleting Rows from a Table
Solution:
SET SERVEROUTPUT ON   DECLARE I_REP_NUM REP.REP_NUM%TYPE;   BEGIN DELETE FROM REP WHERE REP_NUM = '&I_REP_NUM';   END; /

21. Deleting Rows from Multiple Tables
SQL commands can be used to delete more than one row from a table
Problem:
Delete the order whose number is stored in I_ORDER_NUM from the ORDERS table, and then delete each order line for the order whose order number is currently stored in the variable from the ORDER_LINE table.

22. Deleting Rows from Multiple Tables
Solution:
DECLARE I_ORDER_NUM ORDERS.ORDER_NUM%TYPE; W_ORDER_NUM CHAR(5); BEGIN
I_ORDER_NUM := &W_ORDER_NUM; DELETE FROM ORDER_LINE WHERE ORDER_NUM = I_ORDER_NUM; DELETE FROM ORDERS WHERE ORDER_NUM = I_ORDER_NUM; END; /

23. Multiple-Row Select
A SELECT command that retrieves multiple rows poses a problem since PL/SQL can process only one record at a time
This problem can be solved by using a cursor

24. Using Cursors
Cursor: a pointer to a row in the collection of rows retrieved by a SQL command
The cursor advances one row at a time to provide sequential, one-record-at-a-time access to the retrieved rows
By using a cursor, PL/SQL can process the set of retrieved rows as though they were records in a sequential file

25. Using Cursors
Using a cursor in the procedural portion of the program involves three commands:
OPEN: opens the cursor and causes the query to be executed
FETCH: advances the cursor to the next row in the set of rows retrieved by the query and places the contents of the row in the indicated variables
CLOSE: closes a cursor and deactivates it

26. Opening a Cursor
Prior to opening the cursor, there are no rows available to be fetched
The OPEN command to open the CUSTGROUP cursor is:
OPEN CUSTGROUP;

27. Fetching Rows from a Cursor
FETCH: fetch (get) the next row from a cursor
The FETCH command is written as follows:
FETCH CUSTGROUP INTO I_CUSTOMER_NUM, I_CUSTOMER_NAME;

28. Closing a Cursor The CLOSE command is written as follows:
CLOSE CUSTGROUP;

29. Advantages of Cursors The three main advantages of using cursors:
The coding in the program is greatly simplified
In a program using embedded SQL, a special component of the DBMS called the optimizer determines the best way to access the data
If the database structure changes in such a way that the necessary information is still obtainable using a different query, the only change required in the program is the cursor definition

30. Updating Cursors
Data can be updated through a cursor by using the FOR UPDATE OF clause
A WHERE clause can be used to restrict the scope of the update

31. Error Handling
Programs must be able to handle exceptional conditions that can arise when accessing the database
For example, a user might enter a value that would cause an error to occur
Errors can be handled by using the EXCEPTION command

32. Using SQL in Microsoft Access Programs
In Microsoft Access, programs are written in Visual Basic
Visual Basic does not allow the inclusion of SQL commands directly in the code
If the SQL command is stored in a string variable, the DoCmd.RunSQL command can be used to run the command

33. Using SQL in Microsoft Access Programs
The procedure in which you place the SQL command can include arguments
Arguments are values that provide information to the procedure
Example:
In a procedure to delete a sales rep, the argument would be the sales rep number

34. Deleting Rows
To delete the sales rep whose number is 20, the command is:
DELETE FROM REP WHERE REP_NUM = '20';
Usually, the specific sales rep number to delete is not known in advance
It can be passed as an argument to the procedure containing the DELETE command
A procedure is entered in the Microsoft Visual Basic window

35. Microsoft Visual Basic window
Deleting Rows
Microsoft Visual Basic window

36. Running the Code Normally, you run a function by:
Calling it from another procedure
Associating it with some event
Functions can also be run directly by using the Immediate window

37. Running the Code
The Immediate window

38. Running the Code To run a function procedure in the Immediate window:
Type:
A question mark
The name of the procedure
A set of parentheses
Place the values for any arguments in the parentheses
After typing the command, press the Enter key

39. Updating Rows
A procedure can update a table by using an UPDATE command
Such a procedure would be similar to the one used to delete a sales rep

40. Inserting Rows The process for inserting rows is similar
The appropriate INSERT command is created in the strSQL variable
There will be multiple arguments in the procedure—one for each value to be inserted

41. Finding Rows
A SELECT command that returns several rows poses serious problems for record-at-a-time languages like PL/SQL and Visual Basic
For such SELECT commands, the results of a query are handled in the same way as a loop is used to process through the records in a table

42. Summary
To embed a SQL command in a PL/SQL program, type it in the procedural code
Variables in PL/SQL programs are declared after the word DECLARE
To assign variables the same type as a column, use the %TYPE attribute
You can request user input in SQL commands by using prompt variables
If a SELECT command is to retrieve more than one row, define a cursor to select one row at a time

43. Summary
Data in the tables on which a cursor is based can be updated with FOR UPDATE OF
To see whether an error has occurred, use the EXCEPTION command
To use SQL commands in Access, create the command in a string variable
To run the command stored in the string variable, use DoCmd.RunSQL
To process a collection of rows retrieved by a SELECT in Access, use a recordset

44. SQL Project Eight Completed
Good Luck
H. Zamanzadeh