oracle slides04 fp2005 ver 1.0

Programming Using Pro *C
Oracle Day 4
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Objectives

Introduction to Oracle Pre-compilers

Embedded SQL

Pro *C
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Pre-compilers
•
Pre-compilers are tools that allow you to embed SQL statements in the
HLL (High Level Language) source code.
•
Pre-compilers accept SQL statements , translate the SQL statements into
runtime calls , generate a source code that can be compiled, linked and
executed.
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Oracle Pre-compilers
•
Oracle supports pre-compilers for the following HLL,
•
C
•
COBOL
•
Fortran
•
Pascal
•
PL/I
•
Ada
•
Oracle supports all this on different platforms like UNIX,DOS,
NETWARE,WINDOWS,VAX,SUN etc
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Advantages of Pre-compilers
•
Write applications using High level programming language
•
Embed SQL in HLL programs.
•

Automatically convert datatypes
–
between those supported by Oracle and the Programming Language.
•
Transalate SQL queries into appropriate programming language code
automatically
•
Handle errors and warnings
–
using the SQLCA (SQL Communication Area) – Explained further
•
Separate pre-compilation of the program modules and then linking them
together.
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Embedded SQL- Definition
•
SQL statements within a programming language called
Embedded SQL statements.
•
The source code containing the embedded SQL is called
Host program.
•
Embedded SQL statements in the source code begin with
EXEC SQL
•
Example:

EXEC SQL INSERT INTO branch (bcode,location)
VALUES (:br_code.:br_location);
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Embedded SQL Program Dev – The big picture
Embedded SQL
Program
Editor
ORACLE
Pre-compiler
Translated Source
Program
Compiler
Object Program
Linker
Executable
Program
ORACLE Run time
Library(SQLLIB)
Resolve calls
SQL statements replaced
by Library calls
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Embedded SQL- Some Basic Concepts
•
Embedded SQL statements
–
Executable
–
Declarative
•
Host, Indicator and pointer variables
•
Context areas, cursors and active sets
•
Transactions
•
Errors and Warnings
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Executable Statements
•
Result in calls and return codes to Oracle.
•
They are used to connect to the ORACLE database, define, query,
manipulate and control access to the Oracle Database.
•
Example:
–
EXEC SQL insert into branch values(:brcode,:br_location,:br_mgr);

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Declarative Statements
•
All statements that allow you to declare variables(host variables) used in
SQL statements , Communication areas and Oracle objects.
•
Following keywords are used for the respective job:
•
DECLARE for Oracle objects
•
INCLUDE for communication areas
•
WHENEVER for error handling
•
The Declare section statements are needed when the precompiler
MODE=ANSI, if MODE=ORACLE then you may omit the Declare
section statements.
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Example: Using DECLARE
EXEC SQL BEGIN DECLARE SECTION;
int emp_no;
char emp_name[30];

float emp_sales;
short ind_sales;
EXEC SQL END DECLARE SECTION;
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Example: Using INCLUDE
EXEC SQL INCLUDE sqlca;
•
SQLCA is the SQL communication area between Oracle and your Pro
*C program (Explained in further slides)
•
SQLCA is a structure (Structure is given in the appendix slides)
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Host variables
•
Host variables allow communication between Oracle and your program.
•
Host variables must be declared using the host language data types and
rules.
–
Must be prefixed with a colon in SQL statements
–
Data types must be supported by host language.

•
A host variable must not be
–
Used as an array subscript
–
be prefixed with colon in host language statements.
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Host variables
•
Host variables are of two types
–
Input
Program assigns values to input host variables and
passes data to ORACLE
–
Output
ORACLE assigns values to output host variables
and passes data to program
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Indicator Variables
•
Every host variable can be associated with an indicator variable.

•
Used for
–
assigning null values to input host variables.
–
Detect null or truncated values in output host variables.
•
They must be
–
declared in the declare section.
–
Prefixed with a colon(:) in the SQL statement.
•
They cannot be
–
used in the WHERE clause of an SQL statement
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Indicator variables
•
Indicator variables can be used to monitor host variables as follows:
•
For input host variables, indicator variables with a value-
-1 Oracle assigns NULL value to the column.
>=0 Oracle assigns value of host variables
•
For output host variables, Oracle assigns the indicator variables with a

value -
-1 column value is NULL
0 Oracle assigns column value to host
>0 Oracle assigns truncated value to host
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Example: Using Host and Indicator variables
main(){
printf(“Enter the employee number”);
scanf(“%d”,&emp_no);
// usage of host and indicator variables
EXEC SQL select name,ytdsales into :emp_name , :emp_sales:ind_sales
from salesrep where empno = :empno;
if (ind_sales == -1)
printf(“No sales achieved by %s”,emp_name);
else
printf(“sales achieved ny %s is %d”,emp_name,emp_sales);
}
Demo Host & Indicator variables
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•
WHENEVER statement is used to do automatic checking and error handling
•

Syntax:
EXEC SQL WHENEVER <condition> <action>;
<condition>
{ [SQLWARNING] |
[SQLERROR] |
[NOT FOUND]
}
<action>
{ [CONTINUE] |
[DO function_call() | break ]
[goto statement_label] |
[STOP]
}
•
The scope of the WHENEVER is positional, not logical.
WHENEVER
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WHENEVER - Actions
•
CONTINUE
–
Continue with next statement if possible
•
DO {<function>|break}
–
Control transferred to function, at end of routine - control returns to

statement following the failed SQL statement
–
break : Will break from the loop in which the failed SQL statement is
present and transfer control to statement following loop
•
GOTO <label>
–
Control transferred to labeled statement
•
STOP
–
Execution of Program stops, uncommitted work rolled back
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WHENEVER - Example
main()
{
//Some piece of code
EXEC SQL DECLARE emp_cursor FOR SELECT empno,ename
FROM emp;
EXEC SQL OPEN emp_cursor;
EXEC SQL WHENEVER NOT FOUND DO break;
WHILE(1)
{
EXEC SQL FETCH EMP_CURSOR INTO
:EMP_NUMBER,:EMP_NAME;

}
EXEC SQL CLOSE EMP_CURSOR;
}
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Summary
•
The Pro *C pre-compiler
•
SQLCA
•
Host and Indicator variables
•
Using embedded SQL statements
•
Handling errors
•
Using embedded PL/SQL
Appendix A – More about Pro C
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Pointer variables
•
C supports pointers, which point to other variables. One can define

pointers as host variables in the declare section of your program.
EXEC SQL BEGIN DECLARE SECTION;
int *int_ptr;
char *char_ptr;
EXEC SQL END DECLARE SECTION;
•
When using in SQL statements you must prefix the pointer variable with
a colon(:).
EXEC SQL SELECT intcol INTO :int_ptr FROM
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Host arrays
•
When a collection of related items is declared as a host variable it is
called a host array.
EXEC BEGIN DECLARE SECTION;
char emp_name[20][20];
int salary[20];
EXEC SQL END DECLARE SECTION;
•
Likewise a collection of indicator variables is an indicator array.
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Host arrays

•
Host array of pointers are not allowed.
•
Multidimensional host arrays are also not allowed with the exception of
char data type.
•
When used in SQL statements host arrays must not be subscripted.
Demo Host Arrays