DATABASE PROGRAMS CS 260 Database Systems. Overview  Introduction  Anonymous blocks  Oracle’s PL/SQL language basics  Conditions and loops  Cursors.

DATABASE PROGRAMS CS 260 Database Systems

Overview  Introduction  Anonymous blocks  Oracle’s PL/SQL language basics  Conditions and loops  Cursors and SQL commands in PL/SQL  Exception handling  Stored programs  Procedures  Functions  Packages  Triggers

Introduction  A database program is used to automate data processing  It is written using a procedural language extension that is specific to the DBMS  Oracle: PL/SQL “Procedural Language/Structured Query Language”  MySQL: MySQL  Microsoft SQL Server: T-SQL “Transact-SQL”  IBM DB2: SQL PL DB2 also runs PL/SQL

Introduction  Why do we need database programs?  Addresses the limitations of SQL commands SQL has no conditional statements or looping mechanisms Database programs are helpful for importing and exporting data You can only go so far with nested queries An SQL query returns a tabular result set, stored programs can manipulate this format  Why not just put stored program logic in an application? “Stored programs” are accessible to any application using the db Database programs interface directly with the database More efficient in terms of both speed and lines of code DBMS can manage security issues

Introduction  Why might we want to avoid database programs?  They increase the DBMS server’s load  Writing the program logic in an external application may allow for more flexibility  Database programs may be more difficult to debug

Introduction  PL/SQL Example  This stored program identifies the number of days until Christmas CREATE OR REPLACE FUNCTION shopping_days_xmas(current_date IN DATE) RETURN NUMBER IS shopping_days NUMBER; BEGIN shopping_days := TO_DATE('25-DEC-2015', 'DD-MON-YYYY') - current_date; RETURN shopping_days; END;

Introduction  Types of PL/SQL programs  Anonymous blocks Not persistent (not stored in the database) Cannot be called by other programs No parameters/arguments  Stored programs Stored as database objects Procedures Functions Packages Triggers Can be called by other programs Allow parameters/arguments

PL/SQL Language Basics  Basic program structure  Statements may span multiple lines and end with a semicolon  Text is not case sensitive  Basic anonymous block program syntax /* block comment */ DECLARE ; BEGIN ; --line comment EXCEPTION ; END;

PL/SQL Language Basics  Variables  Names must follow the Oracle object naming standard  Names should be descriptive  Naming conventions Use lowercase letters with words separated by underscores Example: current_student_id

PL/SQL Language Basics  PL/SQL is a strongly-typed language  All variables must be declared with a type prior to use  Declaration syntax  Declaration example  Initialization example ; current_student_id NUMBER(6); current_student_id NUMBER(6) := 1;

PL/SQL Language Basics  Common data types  SQL data types VARCHAR2, CHAR NUMBER DATE  Non-SQL data types Integers BINARY_INTEGER, INTEGER, INT, SMALLINT, … Real numbers DEC, DECIMAL, DOUBLE, PRECISION, NUMBERIC, REAL, … BOOLEAN  Composite data types RECORD, TABLE, VARRAY

PL/SQL Language Basics  Reference data types  %TYPE Assumes the data type of a database field Variable declaration example  %ROWTYPE Creates a RECORD data type that holds the data types present in the returned SQL query RECORDS are ordered collections of specific data types %ROWTYPE creates a RECORD according to the types in a result Syntax current_cust_name candy_customer.cust_name%TYPE; %ROWTYPE;

PL/SQL Language Basics  Basic Operators Exponentiation** Multiplication* Division/ Addition/Subtraction+/- Assignment:= Comparison= Concatenation||

PL/SQL Language Basics  Displaying PL/SQL output using Oracle SQL Developer  Enable and/or increase memory buffer Necessary to see PL/SQL output on the console  Output data to the console SET SERVEROUTPUT ON SIZE 4000; DBMS_OUTPUT.PUT_LINE(‘ ’); DBMS_OUTPUT.PUT_LINE(‘Output: ’ || );

PL/SQL Language Basics  Anonymous block example  This program prints the current date to the console in the format “Today is ” SET SERVEROUTPUT ON SIZE 4000; DECLARE todays_date DATE; BEGIN todays_date := SYSDATE; DBMS_OUTPUT.PUT_LINE ('Today is ' || todays_date); END;

PL/SQL Language Basics  Anonymous block example output

Conditions and Loops  Conditional statements  Syntax 0 or more “ELSIF” statements Optional “ELSE” statement IF THEN ; ELSIF THEN ; ELSE ; END IF;

Conditions and Loops  Conditional statement example  This program extends the functionality of the previous program by also indicating whether Christmas is coming or has passed DECLARE todays_date DATE; BEGIN todays_date := SYSDATE; DBMS_OUTPUT.PUT_LINE ('Today is ' || todays_date); IF todays_date > to_date('25-JUN', 'DD-MON') THEN DBMS_OUTPUT.PUT_LINE ('Christmas is coming!'); ELSE DBMS_OUTPUT.PUT_LINE ('Christmas has passed.'); END IF; END;

Conditions and Loops  EXIT WHEN loop (equivalent to Java do-while loop)  Syntax  Example LOOP ; EXIT WHEN ; END LOOP; DECLARE i NUMBER; BEGIN i := 0; LOOP i := i+1; DBMS_OUTPUT.PUT_LINE ('i is ' || i); EXIT WHEN i = 10; END LOOP; END;

Conditions and Loops  WHILE loop (equivalent do Java while loop)  Syntax  Example WHILE LOOP ; END LOOP; DECLARE i NUMBER; BEGIN i := 0; WHILE i < 10 LOOP i := i+1; DBMS_OUTPUT.PUT_LINE ('i is ' || i); END LOOP; END;

Conditions and Loops  FOR loop (equivalent do Java for loop)  Syntax  Example FOR IN.. LOOP ; END LOOP; BEGIN FOR i IN 1.. 10 LOOP DBMS_OUTPUT.PUT_LINE ('i is ' || i); END LOOP; END; You cannot manually update the for loop counter within the loop

Cursors and SQL in PL/SQL  Using SQL within a PL/SQL Program

--create table to store all dates in 2015 CREATE TABLE dates_2015 ( date_value DATE ); --program to insert dates SET SERVEROUTPUT ON SIZE 4000; DECLARE first_date DATE := '01-JAN-2015'; counter INT := 0; BEGIN WHILE counter < 365 LOOP INSERT INTO dates_2015 VALUES (first_date + counter); DBMS_OUTPUT.PUT_LINE(first_date + counter); counter := counter + 1; END LOOP; COMMIT; END; Cursors and SQL in PL/SQL  Example looping program SQL can exist in the same script as PL/SQL DML and Transaction control can exist within PL/SQL

Cursors and SQL in PL/SQL  Using SELECT commands in PL/SQL  Create a “cursor” to allow the PL/SQL program to reference the retrieved values Cursor: “CURrent Set Of Records” Pointer to a memory location on the database server  Cursor types Implicit Explicit

Cursors and SQL in PL/SQL  Implicit cursors  Can be used for SELECT queries that return one (and only one) record The query must return a record  Can be used to assign the column values returned by a SELECT statement into one or more variables  The variables need to be declared, but the cursor itself does not

Cursors and SQL in PL/SQL  Implicit cursors  Syntax  Usage The number of variables in the INTO clause must match the number of fields in the SELECT clause The corresponding field/variable data types must be compatible %TYPE may be useful here SELECT,, … INTO,, … FROM WHERE ;

Cursors and SQL in PL/SQL  Implicit cursor example  This program places the cust_name and cust_addr of the candy_customer with a cust_id = 1 into the program’s curr_cust_name and curr_cust_add variables DECLARE curr_cust_name candy_customer.cust_name%TYPE; curr_cust_add candy_customer.cust_addr%TYPE; BEGIN SELECT cust_name, cust_addr INTO curr_cust_name, curr_cust_add FROM candy_customer WHERE cust_id = 1; DBMS_OUTPUT.PUT_LINE(curr_cust_name); DBMS_OUTPUT.PUT_LINE(curr_cust_add); END;

Cursors and SQL in PL/SQL  Explicit cursors  Can be used for SELECT queries that return zero, one, or multiple records  Can be used to assign the column values returned by a SELECT statement into one or more variables  Both the variables and the cursor need to be declared  Explicit cursors are processed sequentially using a loop The loop typically iterates through each record in the result set The cursor points to the current record

Cursors and SQL in PL/SQL  Using an explicit cursor 1. Declare the cursor in the DECLARE section 2. Open the cursor in the program 3. Fetch the cursor result into PL/SQL program variables 4. Close the cursor

Cursors and SQL in PL/SQL  Explicit cursor example  This program loops through all candy_customer cust_id and cust_name values obtained using a cursor and prints them to the console DECLARE CURSOR customer_cursor IS SELECT cust_id, cust_name FROM candy_customer; curr_id candy_customer.cust_id%TYPE; curr_name candy_customer.cust_name%TYPE; BEGIN OPEN customer_cursor; LOOP FETCH customer_cursor INTO curr_id, curr_name; EXIT WHEN customer_cursor%NOTFOUND; DBMS_OUTPUT.PUT_LINE(curr_id || ' ' || curr_name); END LOOP; CLOSE customer_cursor; END;

Cursors and SQL in PL/SQL  Alternate version of explicit cursor example  Uses a single variable of %ROWTYPE data type instead of separate variables for each field DECLARE CURSOR customer_cursor IS SELECT cust_id, cust_name FROM candy_customer; customer_row customer_cursor%ROWTYPE; BEGIN OPEN customer_cursor; LOOP FETCH customer_cursor INTO customer_row; EXIT WHEN customer_cursor%NOTFOUND; DBMS_OUTPUT.PUT_LINE(customer_row.cust_id || ' ' || customer_row.cust_name); END LOOP; CLOSE customer_cursor; END;

Cursors and SQL in PL/SQL  Processing an explicit cursor  Using a cursor FOR loop Special syntax just for explicit cursors Automatically opens, processes, and closes the cursor Automatically terminates after all cursor records are processed Allows for much less code

Cursors and SQL in PL/SQL  Previous example using a cursor FOR loop DECLARE CURSOR customer_cursor IS SELECT cust_id, cust_name FROM candy_customer; customer_row customer_cursor%ROWTYPE; BEGIN FOR customer_row IN customer_cursor LOOP --process each row DBMS_OUTPUT.PUT_LINE(customer_row.cust_id || ' ' || customer_row.cust_name); END LOOP; END;

Exception Handling  Exception handling  An exception may occur due to a runtime error or an event that violates a business rule  If the exception isn’t handled, the program will terminate and a default error message will be displayed  If the exception is handled, the program can continue executing and/or a custom error message can be displayed

Exception Handling  Program flow with and without exception handling Program Body System displays a default error message and program terminates error Program Body Exception handlers error System can display a custom error message without with Program optionally executes additional statements

Exception Handling  Exception types  Predefined (named) Most common system errors have corresponding named exceptions  User-defined (named) Handle application specific errors (business rules)  Undefined (unnamed) Used for less common system errors Built-in exception handler is associated with the ORA error code number

Exception Handling  Syntax for handling predefined named exceptions DECLARE ; BEGIN ; EXCEPTION WHEN THEN ; END;

Exception Handling  Common PL/SQL named exceptions

Exception Handling  Handling a predefined named exception example  This program retrieves and prints a cust_name to the console, but inappropriately retrieves more than one record using an implicit cursor  The “TOO_MANY_ROWS” named exception is handled DECLARE curr_cust_id candy_customer.cust_id%TYPE; curr_cust_name candy_customer.cust_name%TYPE; BEGIN SELECT cust_name INTO curr_cust_name FROM candy_customer; DBMS_OUTPUT.PUT_LINE(curr_cust_name); EXCEPTION WHEN TOO_MANY_ROWS THEN DBMS_OUTPUT.PUT_LINE('Change your query so it' || ' retrieves only one record'); END;

Exception Handling  Syntax for creating, raising, and handling user-defined exceptions  Declare exception as a variable in the DECLARE section  Raise the exception in the program (in the BEGIN section) when appropriate using the RAISE command DECLARE EXCEPTION; BEGIN RAISE ; EXCEPTION WHEN THEN ; END;

Exception Handling  Creating, raising, and handling a user-defined exception example DECLARE curr_purch_id candy_purchase.purch_id%TYPE := 1; curr_purch_date candy_purchase.purch_date%TYPE; new_delivery_date DATE := '05-SEP-07'; e_invalid_date EXCEPTION; BEGIN SELECT purch_date INTO curr_purch_date FROM candy_purchase WHERE purch_id = curr_purch_id; IF curr_purch_date <= new_delivery_date THEN UPDATE candy_purchase SET delivery_date = new_delivery_date WHERE purch_id = curr_purch_id; ELSE RAISE e_invalid_date; END IF; COMMIT; EXCEPTION WHEN e_invalid_date THEN DBMS_OUTPUT.PUT_LINE('Delivery date cannot be before purchase date, please change it'); END;

Exception Handling  Syntax for handling unnamed exceptions  Unnamed exceptions can be identified by their SQL codes  Named exceptions must be handled first  The SQLERRM function returns a message describing the error Potentially useful when handling an unnamed exception DECLARE ; BEGIN ; EXCEPTION -- handle named exceptions first WHEN OTHERS THEN IF SQLCODE = THEN ; END;

Exception Handling  Handling an unnamed exception example DECLARE new_candy_product_id candy_product.prod_id%TYPE := 100; BEGIN --update an FK value using a non-existent value UPDATE candy_purchase SET prod_id = new_candy_product_id WHERE purch_id = 1; EXCEPTION --...named exception handlers WHEN OTHERS THEN IF SQLCODE = -2291 THEN DBMS_OUTPUT.PUT_LINE('Product ID ' || new_candy_product_id || ' does not exist.'); DBMS_OUTPUT.PUT_LINE('Message: ' || SQLERRM ); END IF; END; SQL code list: http://psoug.org/oraerror.htm

Exception Handling  Exception scope and propagation  Exception handlers only handle exceptions thrown in their BEGIN block  Nested blocks can be created so that outer block execution isn’t impacted by inner block exceptions After an exception is raised and handled, all uncommitted transactions are rolled back Execution resumes in the outer block

Exception Handling  Nested block syntax DECLARE ; BEGIN ; DECLARE ; BEGIN ; EXCEPTION ; END; ; EXCEPTION ; END;

Exception Handling  Suppose the cust_type of “W” was assumed to be removed and updated for all customers in our candy database  Write an anonymous block that does the following:  Print the name and cust_type of each customer  If the cust_type is anything other than ‘P’ or ‘R’, raise a custom “invalid_cust_type” exception  If this exception is raised, the program should print the name and invalid cust_type and continue processing

Stored PL/SQL Programs  Can be executed by other programs and users  Can accept input parameters  They’re database objects  Permissions must be granted as needed  Names must be unique in their schemas  Follow object naming standards and conventions  Stored in a compiled form  Types of stored PL/SQL programs  Procedures  Functions  Packages  Triggers

Stored PL/SQL Programs  Parameter modes  IN Default parameter mode (used if no mode is specified) Used to pass values into the program Similar to Java’s pass-by-value argument passing scheme  OUT Used to pass values out of the program Useful for procedures as they cannot “return” values Acts like an uninitialized variable It should be assigned a value  IN OUT Used to both pass values into and out of the program Similar to C++’s pass-by-reference argument passing scheme

Stored Procedures  Stored procedures allow parameters, can call other programs, but cannot return a value  Syntax CREATE OR REPLACE PROCEDURE (,, …) IS ; BEGIN ; EXCEPTION ; END; / “AS” can be used in place of “IS” Header Body

Stored Procedures  Stored procedure example CREATE OR REPLACE PROCEDURE update_delivery_date (curr_purch_id IN candy_purchase.purch_id%TYPE, new_delivery_date IN DATE) IS -- local variable curr_purch_date candy_purchase.purch_date%TYPE; BEGIN -- implicit cursor (only one row returned) SELECT purch_date INTO curr_purch_date FROM candy_purchase WHERE purch_id = curr_purch_id; IF curr_purch_date <= new_delivery_date THEN UPDATE candy_purchase SET delivery_date = new_delivery_date WHERE purch_id = curr_purch_id; DBMS_OUTPUT.PUT_LINE('Delivery date updated'); END IF; COMMIT; END; /

Stored Procedures  Calling a stored procedure  Stored procedures can be called from an SQL script or a PL/SQL program  SQL script syntax  Example  PL/SQL example (anonymous block) EXECUTE (<comma separated list of arguments); EXECUTE update_delivery_date (1, SYSDATE); BEGIN update_delivery_date (1, SYSDATE); END;

Stored Functions  Stored functions are similar to stored procedures, but they return a single value  Syntax CREATE OR REPLACE FUNCTION (,, …) RETURN IS ; BEGIN ; RETURN ; EXCEPTION ; RETURN ; END; / “AS” can be used in place of “IS” Header Body Exception handlers should return a value

Stored Functions  Stored function example  Example call from an SQL script CREATE OR REPLACE FUNCTION calc_diff (date1 IN DATE, date2 IN DATE) RETURN NUMBER IS days_passed NUMBER; BEGIN days_passed := date1 - date2; RETURN days_passed; END; / SET SERVEROUTPUT ON SIZE 4000; EXEC DBMS_OUTPUT.PUT_LINE(calc_diff('25-DEC-2014', SYSDATE));

Stored Functions  Calling a stored function  Stored functions can also be called from within an SQL statement or a PL/SQL program  Syntax Can be called anywhere a value of the return type is allowed  Examples SELECT purch_id, calc_diff(delivery_date, purch_date) FROM candy_purchase; SELECT purch_id FROM candy_purchase WHERE calc_diff(delivery_date, purch_date) > 0;

Packages  A package is an object that groups related PL/SQL objects, such as variables, cursors, procedures, and functions  It consists of a specification and a body  Specification Declares a public interface  Body Contains a private implementation  Clients can reference and call objects declared in the specification, but not those declared in the body  Similar to header and source files in C++

Packages  Benefits of packages  Encapsulation of related objects  Information hiding Clients cannot see the implementation details in the body If a procedure is declared in the body (and not the specification), it can be called only from within the package body  Better performance Package specifications and bodies are compiled separately If changes to the body are needed, only the package body needs to be recompiled instead of all clients that call objects in the package body

Packages  Package specification syntax CREATE OR REPLACE PACKAGE IS --public variables and cursors ; CURSOR IS ; … --procedures & functions PROCEDURE ( ); FUNCTION ( ) RETURN ; … END; /

Packages  Package specification example  The public variables “max_pounds” and “curr_purch_id” can be used within the “update_pounds” and “update_delivery_date” implementations They can also be used anywhere access to the package is allowed CREATE OR REPLACE PACKAGE purchase_package IS --public variable declarations max_pounds NUMBER := 100; curr_purch_id candy_purchase.purch_id%TYPE; --procedure declarations PROCEDURE update_pounds (new_pounds IN NUMBER); PROCEDURE update_delivery_date (new_delivery_date IN DATE); END; /

Packages  Example package body CREATE OR REPLACE PACKAGE BODY purchase_package IS PROCEDURE update_delivery_date (new_delivery_date DATE) IS curr_purch_date candy_purchase.purch_date%TYPE; BEGIN SELECT purch_date INTO curr_purch_date FROM candy_purchase WHERE purch_id = curr_purch_id; IF curr_purch_date <= new_delivery_date THEN UPDATE candy_purchase SET delivery_date = new_delivery_date WHERE purch_id = curr_purch_id; END IF; COMMIT; END; PROCEDURE update_pounds (new_pounds NUMBER) IS BEGIN IF new_pounds <= max_pounds THEN UPDATE candy_purchase SET pounds = new_pounds WHERE purch_id = curr_purch_id; END IF; COMMIT; END; / Procedure 1 Procedure 2

Packages  When referencing or calling an object in a package, it is prefaced with its package name  Syntax  Example (called from an SQL script) The EXECUTE command isn’t used when referencing or calling package objects from within a PL/SQL block For example, dbms_output.put_line(‘…’); is an example of calling a procedure inside the dbms_output package. ; EXECUTE purchase_package.curr_purch_id := 1; EXECUTE purchase_package.update_pounds(3.7);

Packages  When creating a package body, use the SHOW ERRORS command to print errors to the console  Oracle built-in packages  Provide support for basic database functionality  Owned by the SYS database schema  Visible using the “Connections” pane in Oracle SQL Developer Expand your schema > Other Users > SYS > Packages / SHOW ERRORS;

Triggers  Database triggers are programs that are attached to specific database tables  They may be executed in response to the following table operations:  INSERT  UPDATE  DELETE

Triggers  Why are triggers useful?  Force related operations to always happen Update a “quantity on hand” field whenever an item is sold Update a “current enrollment total” field whenever a student enrolls in a course section  Create an audit trail Record the username and IP address of every user who changes a table For example, record who changed a student grade, when they changed it, what they changed it from, and what they changed it to

Triggers  When defining a trigger, the following must be specified:  Operation that causes the trigger to fire INSERT, UPDATE, or DELETE  Timing BEFORE or AFTER the operation occurs  Level STATEMENT or ROW

Triggers  Trigger timing  BEFORE The trigger fires before the statement executes For example, for an audit trail, record the old grade value before it is updated Though it’s still possible to accomplish this using AFTER  AFTER The trigger fires after the statement executes For example, update the “quantity on hand” after an item is sold

Triggers  Trigger levels  ROW The trigger fires once for each row that is affected For example, update a corresponding “quantity on hand” value for each item that was sold  STATEMENT The trigger fires once regardless of how many rows are updated For example, for an audit trail, you just want to record that someone updated a table, but you don’t care how many rows were updated

Triggers  Restrictions  Triggers cannot have any parameters  Triggers can only be created on tables that you own  Triggers cannot execute a COMMIT command This is handled by the transaction firing the trigger  Triggers can be enabled or disabled ALTER TRIGGER ;

Triggers  Creation syntax  Choose one of “BEFORE” or “AFTER”  Choose one or more of “INSERT”, “UPDATE”, and “DELETE”, separated by “OR”  “FOR EACH ROW” is optional The trigger has statement level if omitted  “WHEN ( )” is optionally used only at the ROW level Causes trigger to fire only when the row satisfied the condition CREATE OR REPLACE TRIGGER ON [FOR EACH ROW] [WHEN ( )] BEGIN ; END; /

Triggers  Statement level example CREATE TABLE purchase_audit( date_changed DATE, user_changing VARCHAR2(30) ); CREATE OR REPLACE TRIGGER purchase_audit AFTER INSERT OR UPDATE OR DELETE ON candy_purchase BEGIN INSERT INTO purchase_audit VALUES (SYSDATE, USER); END; / SHOW ERRORS; UPDATE candy_purchase SET pounds = 4.5 WHERE purch_id = 1 AND prod_id = 1; SELECT * FROM purchase_audit; USER returns the database user executing the statement

Triggers  Row level example CREATE TABLE purchase_audit_row (purch_id NUMBER(9), old_pounds NUMBER, new_pounds NUMBER, change_date DATE, change_user VARCHAR2(30)); CREATE OR REPLACE TRIGGER purchase_audit_row BEFORE UPDATE ON candy_purchase FOR EACH ROW BEGIN INSERT INTO purchase_audit_row VALUES( :OLD.purch_id, :OLD.pounds, :NEW.pounds, SYSDATE, USER); END; / SHOW ERRORS; SELECT * FROM purchase_audit_row; UPDATE candy_purchase SET pounds = 15 WHERE purch_id = 5; SELECT * FROM purchase_audit_row; :OLD. references a field’s old value :NEW. references a field’s new value

Triggers  Trigger design (from Oracle)  Triggers should not duplicate features already built into the database E.g. Checking constraints  If size is much more than 60 lines, place logic in a stored procedure and call from the trigger  Triggers should not be recursive For example, a trigger should not update a table if it’s been designed to fire after updates are made to that table Causes out of memory errors  Because of their potentially frequent use, they should be designed and implemented carefully

PL/SQL Programs in Scripts  Using PL/SQL programs in scripts  PL/SQL programs in a script must be followed by a single forward slash CREATE OR REPLACE PACKAGE show_message IS PROCEDURE hello_world; END; / CREATE OR REPLACE PACKAGE BODY show_message IS PROCEDURE hello_world IS BEGIN DBMS_OUTPUT.PUT_LINE('Hello World'); END; / SET SERVEROUTPUT ON SIZE 4000; BEGIN show_message.hello_world(); END; /

DATABASE PROGRAMS CS 260 Database Systems. Overview  Introduction  Anonymous blocks  Oracle’s PL/SQL language basics  Conditions and loops  Cursors.

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DATABASE PROGRAMS CS 260 Database Systems. Overview  Introduction  Anonymous blocks  Oracle’s PL/SQL language basics  Conditions and loops  Cursors.

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Presentation on theme: "DATABASE PROGRAMS CS 260 Database Systems. Overview  Introduction  Anonymous blocks  Oracle’s PL/SQL language basics  Conditions and loops  Cursors."— Presentation transcript:

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