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Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 22Ć2Schedule: Timing Topic 40 minutes Lecture 45 minutes Practice 85 minutes Total Class Management Note: Files required fo

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Interacting with Oracle

22

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Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 22Ć2

Schedule: Timing Topic

40 minutes Lecture

45 minutes Practice

85 minutes Total

Class Management Note:

Files required for lesson

Demonstration: l22cust.pls, l22newsd.pls, l22delr.pls

Practice: None

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Interacting with Oracle 22Ć3

In this lesson, you access the database and control transactions through SQL statements in PL/SQL.

At the end of this lesson, you should be able to

D Use SELECT, INSERT, UPDATE, and DELETE commands in PL/SQL

subprograms

D Determine the outcome of SQL statements by using implicit cursor attributes

D Control transactions within PL/SQL

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Remind students that they will combine the commands covered in thislesson with the subprograms learned in the previous lessons

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When you need to extract information from or apply changes to the database, youmust use SQL PL/SQL supports full data manipulation language and transactioncontrol commands within SQL You can use SELECT statements to populate

variables with values queried from a row in a table Your DML commands canprocess multiple rows

Comparing SQL and PL/SQL Statement Types

D A PL/SQL block is not a transaction unit Commits, savepoints, and rollbacks areindependent of blocks, but you can issue these commands within a block

D PL/SQL does not support data definition language (DDL), such as CREATETABLE, ALTER TABLE, or DROP TABLE

D PL/SQL does not support data control language (DCL), such as GRANT orREVOKE

D DBMS_SQL package allows you to issue DDL and DCL statements

DBMS_SQL package is a new package available in Oracle7 Release 7.2

For more information about DBMS_SQL package, see Oracle7 Server

Application Developer’s Guide, Release 7.2.

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The INTO clause is required in a SELECT statement in PL/SQL This is incontrast to SQL, where the INTO clause is forbidden

Output variables are PL/SQL variables through which values pass from thedatabase out to the PL/SQL block The datatype of an output variable must

be compatible with the datatype of the source column, although the sourcecolumn may be an expression; in particular, Boolean variables are notpermitted

Input variables are PL/SQL variables through which values pass from thePL/SQL block into the database

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Use the SELECT statement to retrieve data from the database The SELECT

statement contains an additional mandatory clause: the INTO clause In the INTOclause, list the output variables for receiving the data The SELECT statement mustreturn exactly one row or an error will occur

where: select_list is a list of at least one column, and can include

SQL expressions, row functions, or groupfunctions

variable_name is the scalar variable to hold the retrieved value

record_name is the PL/SQL RECORD to hold the retrieved

values

table specifies the database table name

condition is composed of column names, expressions,

constants, and comparison operators, includingPL/SQL variables and constants

Take advantage of the full range of Oracle7 Server syntax for the SELECT statement.Guidelines

D Terminate each SQL statement with a semicolon (;)

D Assign values into PL/SQL tables in a loop by declaring an explicit cursor

D The INTO clause is required for the SELECT statement when it is embedded

within PL/SQL

D The WHERE clause is optional, and can be used to specify input variables,constants, literals, or PL/SQL expressions

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Guidelines

D Specify the same number of output variables in the INTO clause as databasecolumns in the SELECT clause Be sure that they correspond positionally and thattheir datatypes are compatible

D Ensure that the datatype of the identifiers match the datatype of the columns byusing the %TYPE attribute The datatype and number of variables in the INTOclause match those in the SELECT list

D Terminate the PL/SQL block with the END statement You can add the name ofthe subprogram after the keyword END for clarity

D Include at least one RETURN statement in a function

D Use group functions, such as SUM, in a SQL statement since group functionsapply to groups of rows in a table

On the board, write: v_sum_salaries := SUM (s_emp.salary),and draw a line through it to emphasize that group functions must be used

in a SQL statement

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Question: Ask students what the record structure looks like

Answer: Three fields, ID, NAME, and REGION_ID

Question: Ask students how to reference the value in the NAME field of therecord

Answer: Reference the value as DEPT_RECORD.NAME

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A PL/SQL RECORD can be used to easily create fields that match a database table’scolumns Each field has the same name and datatype as a column in the table Whenretrieving all columns from a table, use a PL/SQL RECORD to hold the retrievedvalues

Note for page 22-16

Question: Ask students how to change the code to avoid receiving the error

Answer: Name the identifiers with the v_ prefix.

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Avoid ambiguity in the WHERE clause by adhering to a naming convention thatdistinguishes database column names from PL/SQL variable names

Example

Retrieve the order date and the ship date for the specified order This example raises

an unhandled runtime exception.

SELECT date_ordered, date_shipped

INTO date_ordered, date_shipped

ERROR 0 at line 1, column 0

Unhandled exception ORA-01422: exact fetch returns

more than requested number of rows

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Exceptions are covered in a later lesson

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SELECT statements within a PL/SQL block fall into the “Embedded SQL”ANSI

classification Be sure that the SELECT statement retrieves exactly one row;

otherwise an exception is raised An exception is an error that terminates a PL/SQLblock

SELECT Exceptions

The SELECT statement identifies more

than one row

TOO_MANY_ROWS exception(Oracle7 Server error number -1422).The SELECT statement does not identify

any rows

NO_DATA_FOUND exception (Oracle7Server error number +1403)

Note: Handle the raised exceptions with exception-handling routines, which will be

covered in a later lesson Alternatively, fetch multiple rows one-by-one in aloop by declaring an explicit cursor

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TOO_MANY_ROWS Exception

When more than one record is identified with a SELECT statement, Oracle7 Serverraises an error number -1422, also referred to as TOO_MANY_ROWS, which is thepredefined exception name

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Manipulate data in the database by using the DML commands

D INSERT statement adds new rows of data to the table

D UPDATE statement modifies existing rows in the table

D DELETE statement removes unwanted rows from the table

Inserting Data

When adding rows to a table, you can eliminate unnecessary IN arguments

D Use SQL function, such as USER and SYSDATE

D Generate primary key values by using database sequences

D Derive values in the PL/SQL block

D Add column default values

Technical Note:

There is no possibility for ambiguity with identifiers and column names inthe INSERT statement Any identifier in the INSERT clause must be adatabase column name

DEMO: l22cust.pls

PURPOSE: This example demonstrates using the INSERT commandsembedded in a procedure

1 Select from the menu File—>Load, and load the l22cust.pls file.

2 Show the code to the students

3 Execute the procedure at the Interpreter prompt

Enter: cust_order(201);

4 Verify the change to the table Enter: SELECT * FROM s_ord

WHERE customer_id = 201;

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Updating and Deleting Data

There may be ambiguity in the SET clause of the UPDATE statement because

although the identifier on the left of the assignment operator is always a databasecolumn, the identifier on the right can be either a database column or a PL/SQLvariable

Remember that the WHERE clause is used to determine which rows are affected If

no rows are modified, no error occurs, unlike the SELECT statement in PL/SQL

Technical Note:

PL/SQL variable assignments always use “:=”; SQL column assignmentsalways use “=”

Recall that if column names and identifier names are identical in the

WHERE clause, the Oracle7 Server looks to the database first for the name

DEMO: l22newsd.pls

PURPOSE: Show the use of parameters in a procedure to update a value inthe table

1 Select from the menu File—>Load, and load the l22newsd.pls file.

Enter: new_ship_date(101,’7-Nov-95’);

4 Verify the change to the table

Enter: SELECT * FROM s_ord WHERE id = 101;

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Whenever you issue a SQL command, the Server opens an area of memory in which

the command is parsed and executed This area is called a cursor.

When the executable part of a block issues a SQL command, PL/SQL creates animplicit cursor, which has the SQL identifier PL/SQL manages this cursor

automatically An explicit cursor is explicitly declared and named by the programmer.There are four attributes available in PL/SQL that can be applied to cursors

Note: More about explicit cursors will be covered in Lesson 24.

SQL Cursor Attributes

You can use these attributes in PL/SQL statements as you would functions, but not inSQL commands They are useful to evaluate the result of a DML operation PL/SQLdoes not consider a data manipulation language statement that affects no rows to havefailed, unlike the SELECT statement, which returns an exception

Attribute Description

SQL%ROWCOUNT Number of rows affected by the most recent SQL

statement (an integer value)

SQL%FOUND Boolean attribute that evaluates to TRUE if the most

recent SQL statement affects one or more rows.SQL%NOTFOUND Boolean attribute that evaluates to TRUE if the most

recent SQL statement does not affect any rows.SQL%ISOPEN Always evaluates to FALSE because PL/SQL closes

implicit cursors immediately after they are executed

For more information, see

PL/SQL User’s Guide and Reference, Release 2.3, Chapter 4, “Implicit Cursor

Attributes” section

You can also use the attributes in the EXCEPTION section of a block toevaluate the results of a failed SELECT statement This topic will be

covered in a later lesson

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DEMO: l22delr.pls

PURPOSE: Show students that the SQL cursor attributes indicate thenumber of rows affected Show that if no rows are deleted, there is no error,unlike with the SELECT statement, which produces an exception

Procedure Builder instructions:

1 Select from the menu File—>Load, and load the l22delr.pls file.

Enter: del_rows(100);

4 Roll back the changes when done

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DELETE FROM s_item

WHERE ord_id = v_ord_id;

1 Show the code in the l22delrs.sql file.

2 Start the file to create the procedure

3 Create the global variable to print out the result

Enter: variable g_rows_deleted VARCHAR2(25)

4 Execute the procedure at the prompt

Enter: execute del_rows(100, :g_rows_deleted);

5 Print the results Enter: print g_rows_deleted

6 Roll back the changes when done

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Control the logic of transactions with COMMIT and ROLLBACK SQL commands,rendering some groups of database changes permanent, while discarding others Aswith Oracle7, DML transactions start at the first command to follow a COMMIT orROLLBACK, and end on the next successful COMMIT or ROLLBACK Theseactions may occur within a PL/SQL block or as a result of events in the host

environment (for example, ending a Procedure Builder session automatically commitsthe pending transaction)

You can also include explicit locking commands (such as LOCK TABLE and

SELECT FOR UPDATE) in a block They take effect until the end of the

where: WORK is for compliance with ANSI standards

Note: A transaction is defined as a sequence of SQL statements.

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SAVEPOINT Command

Alter the transactional logic with Oracle7 Server savepoints based upon runtimeconditions SAVEPOINT marks an intermediate point in the transaction processing.Syntax

SAVEPOINT savepoint_name;

ROLLBACK TO SAVEPOINT discards pending changes made after the savepointwas marked

Syntax

ROLLBACK [WORK] TO [SAVEPOINT] savepoint_name;

where: savepoint_name is a PL/SQL identifier

Technical Note:

SAVEPOINT is not ANSI standard It is an Oracle extension of the standardSQL language You can have more than one savepoint per transaction, eachidentified by a different marker name If you create a second savepoint withthe same marker name, the previous savepoint is erased Savepoints areespecially useful with conditional logic

Question: How many rows are inserted?

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You can embed SQL within the PL/SQL block You can use the following validcommands:

Statement Description

SELECT Retrieves exactly one row into scalar variables or into a

record variable

UPDATE Modifies one or more existing rows

DELETE Removes one or more existing rows

COMMIT Makes all pending transactions permanent

ROLLBACK Eliminates all pending transactions

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In this practice, you create three procedures to input, update, and delete information

in a table, all using DML statements within a PL/SQL block

Practice Contents

D Creating a procedure to insert data into a table

D Creating a procedure to update data in a table

D Creating a procedure to delete a record from a table

D Verifying your changes to the table using Oracle Procedure Builder built-ins andimplicit cursor attributes

Duration: 45 minutes

For additional exercises, see Practice 26, Exercises 1a and 1d

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If you are not already connected to the database, be sure to connect now

1. Create a procedure to insert a new department into the S_DEPT table

a. Use the S_DEPT_ID sequence generator for the department number

b. Create a parameter for the department name

c. Leave the region number null for now

d. Execute the procedure

e. Display the new department that you created

2. Create a procedure to update the region number for an existing department

a. Create a parameter for the department number

b. Create a parameter for the region name

c. Set the region number to the value that corresponds to the specified regionname

d. Test the procedure What happens if you enter a region name that does notexist?

e. Display the department number, region number, and region name for theupdated department

3. Create a procedure to delete the department created in Exercise 1

a. Create a parameter for the department number

b. Print to the screen the number of rows affected

c. Test the procedure What happens if you enter a department number that doesnot exist?

What happens if you enter a department that has employees?

d. Confirm that the department has been deleted

Tiêu đề	Introduction to Oracle: SQL and PL/SQL Using Procedure Builder
Trường học	Unknown University
Chuyên ngành	Computer Science
Thể loại	Lecture Notes

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