A Guide to SQL, Seventh Edition. Objectives Embed SQL commands in PL/SQL programs Retrieve single...

A Guide to SQL, Seventh Edition

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


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


Introduction

A procedural language requires a step-by-step process to accomplish tasks

You can embed, or include, SQL commands in the programs using procedural languages

Useful when needed tasks are beyond the capabilities of SQL


Using Prompt Variables

Sources of input for SQL commands

Onscreen form

Passed as arguments from procedure

Prompt variables

Prompt variables are when user is prompted to enter a value when the program is run

Precede the variable with an “&”


PL/SQL Programs

Embed SQL commands in PL/SQL programs

Create and save the programs as script files

Run the script files to run the programs


Retrieving a Single Row and Column

To place the results of a command in a variable, use the INTO clause

SELECT LAST_NAMEINTO I_LAST_NAMEFROM REPWHERE REP_NUM = ‘&I_REP_NUM;’



When executed, user will be prompted for a value for I_REP_NUM

That value will be used to retrieve the last name of the sales rep whose number equals this value

The results will be placed in the variable I_LAST_NAME

This variable can be used in another program



Procedure uses one argument and produces a single line of text containing this argument output

To see the output, execute the command

SET SERVEROUTPUT ON

Include this command in the PL/SQL program to ensure it will be executed



Procedural code are commands that specify exactly what program is to do

Procedural code located between BEGIN and END commands

Each variable declaration and command as well as the word END are followed by semicolons



The slash (/) at the end of the program appears on its own line

When the script is run, the slash causes commands in the program to be executed immediately

With the slash, commands are only loaded into memory

Typing the slash runs the program


Using the %TYPE Attribute

The %TYPE attribute ensures the variable has the same type as a particular column in a table

Do not enter a data type it is automatically assigned from the corresponding column

I_REP_NUM REP.REP_NUM%TYPE


Retrieving a Single Row from a Join Use embedded SQL commands to join tables


Inserting a Row into a Table When updating a database from the PL/SQL program, use

appropriate SQL commands


Changing a Single Row in a Table

Use the SQL command to insert rows in a database


Deleting Rows from a Table

SQL commands are used to delete rows from a table


Multiple-Row Select

PL/SQL can process only one record at a time

A cursor is a pointer to a row in the collection of rows retrieved by a SQL command

A cursor advances one row at a time to provide sequential one-record-at-a-time access to retrieved rows


Using Cursors

The first step is to declare the cursor and describe the associated query in the declaration section

CURSOR CUSTGROUP ISSELECT CUSTOMER_NUM, CUSTOMER_NAMEFROM CUSTOMERWHERE REP_NUM = ‘&I_REP_NUM’;

Three commands are needed

OPEN, FETCH, CLOSE


Opening a Cursor

OPEN command

Opens cursor

Causes query to be executed

Makes results available to the program

Prior to opening, there are no rows available to be fetched

OPEN CUSTGROUP


Fetching Rows from a Cursor

FETCH command Advances cursor to next row in set of retrieved

rows

Places contents of row in indicated variables

FETCH CUSTGROUP I_CUSTOMER_NUM,I_CUSTOMER_NAME;

Execution of fetch command produces only a single row


Closing a Cursor

CLOSE command Closes a cursor Deactivates it Data retrieved by execution of the query is no longer

available


More Complex Cursors

Any SLQ query is legitimate in a cursor definition

More complicated retrieval requirements result in greater benefits


Advantages of Cursors

Simplified coding in the program Progams with embedded SQL utilizes the

optimizer Programmer doesn’t worry about the best way to

retrieve data Program doesn’t have to change even if the

underlying structure does Cursor definition only changes; not procedural

code


Updating Cursors

Update the rows encountered in processing cursors with FOR UPDATE OF


Error Handling

Handle errors with the EXCEPTION command


Using SQL in Microsoft Access Programs

In Access, programs are written in Visual Basic

Does not allow inclusion of SQL commands in the code

If the SQL command is store in string variable, use the DoCmd.RunSQL command


Deleting Rows

Place the SQL command in the procedure, including arguments

Example

DELETE FROM REP WHERE REP_NUM = ’20’


Running the Code

Normally run by calling it from another procedure or by associating it with an event

Can be run by using the Immediate window

Normally for testing


Updating Rows

Similar to the procedure to delete a sales rep, except

Need the UPDATE command

Two arguments rather than one

• Two portions of the construction of the SQL command that involve variables


Inserting Rows

Process is similar

Create the appropriate INSERT command in the strSQL variable

Multiple arguments

Once for each value inserted


Finding Rows

SELECT commands handled differently than in PL/SQL

No cursors

Handle results of query just as you would use a loop to process through the records on the table


Summary

How to embed SQL commands in PL

Created programs Retrieved single rows

Inserted new rows

Changed and deleted existing rows

Cursors to update database

Error Handling

Using SQL command in Access


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