1. Embedded DB2

2. Agenda Supporting Embedded SQL Coding Aids Program Preparation
Delimiters
Host Variables
Indicator Variables
SQLCA
Coding Aids
Program Preparation
Using Cursors

3. Supporting Embedded SQL

4. Objectives
Embed INSERT, UPDATE, DELETE and single row SELECT statements in application programs
Effectively communicate with DB2 by using indicators and the SQLCA block
Demonstrate use of DB2 coding aids

5. Supporting Embedded SQL
Use delimiters to identify SQL statements in the application
Use host variables to provide values on the WHERE clauses or receive values from SELECT statements
Use Indicator variables to provide null data
Use the SQLCA to determine success or failure of SQL statements

6. Delimiters
Used by PRECOMPILER to identify SQL statements to be translated
Must indicate beginning and end of each embedded SQL statement
C and C++ Delimiters
EXEC SQL <SQL statement> ;
The keywords EXEC SQL must appear on the same line

7. Delimiters in C and C++
EXEC SQL UPDATE TEMPL SET WORKDEPT = ‘C02’ WHERE WORKDEPT = ‘C01’ ;

8. Host Variables (I) C Andy gets(sname); User Inputs a Value name Andy
ESQL
where sname= :name
Optional, used to set a value before statement is executed
Host variables must be preceded by a colon
Host variables must match column data types

9. Host Variables (II) Interactive SQL statement
INSERT INTO S (s#, sname) VALUES (‘000122’, ‘Claven’)
SQL Statement in A Program
EXEC SQL INSERT INTO S (s#,sname) VALUES (:sid, :sname) ;
000122
Claven
sid sname

10. Host Variables (III) Interactive SQL statement
UPDATE SC SET score = score * 1.05 WHERE c# = ‘c01’
SQL Statement in A Program
EXEC SQL UPDATE SC SET score = score * :ratio WHERE c#= :cid ;
1.05
c01
ratio
cid

11. Host Variable (IV) To Receive a Value SELECT........INTO :a ..... a
Required with SELECT statement
One HOST VARIABLE for each COLUMN SELECTed
Additional variable used for indicating NULL characteristic
SELECT INTO syntax can only be used to return one or zero rows. GROUP BY, HAVING, ORDER BY are not permitted.

12. Host Variables Declaration
EXEC SQL BEGIN DECLARE SECTION; (Declaration of all host variables referenced within SQL statements) EXEC SQL END DECLARE SECTION;
Global to a module
Multiple declare sections may be used in one source file

13. Declaration Considerations For C
CREATE TABLE SIMPLE (title char(20), number smallint)
EXEC SQL BEGIN DECLARE SECTION; char title[21]; short number; EXEC SQL END DECLARE SECTION; main() { EXEC SQL SELECT TITLE INTO :title FROM SIMPLE WHERE number= :number; }

14. Indicator Variables(I)
SELECT col1 INTO :a:ind a
aind -
value
INDICATOR VARIABLE (SMALLINT) is required if SELECTed column allows NULL.
If column is NULL, INDICATOR VARIABLE is set to negative value, VALUE VARIABLE is untouched.
INDICATOR VARIABLE can be set to negative value by program to indicate NULL on UPDATE or INSERT

15. Indicator Variable (II)
If DB2 attempts to indicate the presence of a NULL and the program does not provide an indicator variable, an error results.
Sample C declare for an indicator: EXEC SQL BEGIN DECLARE SECTION; short aind; char a[9]; EXEC SQL END DECLARE SECTION;

16. Indicator Logic Example
EXEC SQL
SELECT phoneno, sex
INTO :phoneno:phoneind, :sex
FROM TEMPL
WHERE empno = :eno;
if (phoneind < 0)
null_phone();
else
good_phone();

17. Indicator Variable Usage NULL Values
HOST VAR IND. VAR COLUMN
:cd :cdi jobcode
unchanged < 0 NULL
N/A <0 NULL
SELECT/
FETCH
UPDATE/
INSERT
: Controlled By DB2
: Controlled By Program

18. Indicator Variable Usage Truncation
If an indicator variable has a positive value, a truncation occurred.
If the seconds portion of a TIME data type is truncated, the indicator variable contains the second portion of the data.
For all other data types, the indicator variable represents the length of the data in the database column.

19. SQLCA - SQL Communication Area
Information/SQLCODE
Program
SQLCA
DB2
SQL
An ESQL application program must either provide a structure named SQLCA or a stand-alone integer variable named SQLCODE.

20. SQLCA Code Condition SQLCODE SQLWARNO REQUEST STATUS
ERROR < FAILED
WARNING > 0 & != OR ‘W’ SPECIAL COND.
NOT FOUND DATA NOT FOUND
SUCCESS AND ‘ ‘ SUCCESS

21. Coding Aids WHENEVER Statement for exception handling
INCLUDE statement and INCLUDE files
to add SQLCA structure to program and to provide function prototypes

22. WHENEVER Statement EXEC SQL WHENEVER condition action; Conditions:
SQLERROR - negative SQLCODE
SQLWARNING - position SQLCODE(not +100) or SQLWARNO = ‘W’
NOT FOUND - SQLCODE = +100
Actions:
GOTO :X
CONTINUE
Program continues with next statement
used to cancel effect of prior WHENEVER

23. WHENEVER Example EXEC SQL WHENEVER SQLWARNING GOTO :w;
EXEC SQL WHENEVER NOT FOUND GOTO :m;
EXEC SQL WHENEVER SQLERROR GOTO :oh_no;
EXEC SQL WHENEVER SQLERROR CONTINUE;

24. SQL Include Statement file.sqc file.c
EXEC SQL INCLUDE SQLCA;
EXEC SQL BEGIN DECLARE SECTION;
EXEC SQL INCLUDE ‘myfile.h’;
EXEC SQL END DECLARE SECTION;
struct sqlca .... };
struct sqlca sqlca;
/* myfile.h contains my host variables */
If myfile.h contains host variable declarations, it must be included with the EXEC SQL INCLUDE.

25. Include Files #include <sqlca.h> struct sqlca sqlca;
#include <sql.h>
functions prototypes for certain API’s including error message retrieval.
sqlda.h : defines the SQL Descriptor Area(SQLDA)
sqlenv.h : language-specific calls for database environment APIs, and the structure, constants, and return codes for those interfaces.
sqlutil.h : language-specific calls for the utility APIs, and the structure, constants, and return codes for those interfaces.

26. Program Preparation

27. Objectives
Identify the additional steps necessary to prepare a program that contains embedded SQL for execution
describe the functions of the DB2 PRECOMPILE and BIND processes

28. Precompile(I) P Database R Tables Services E Indexes C myapp.sqc
Package
myapp.sqc
Source File
myapp.c
Name of package:
The same as the
name of the source
module truncated to
8 characters
Modified
Source File

29. Precompile(II) PREPARE or PREP
By Default, PREP creates a package directly in the database.
By Default the PREP produces two output
Modified source file: Replace SQL with host language calls
Use DB2 Optimizer to create an access strategy called package
Index?
Object exists?
Authority?
Time Stamp: Include in package and modified source file
db2 PREP myapp.sqc

30. Compile and Link
The modified source file is compiled and linked normally, producing an executable file.
gcc -I/usr/include -ldb2 myapp.c -o myapp

31. Program Execution Package Tables Myapp Database Services
Executable File

32. Precompile with Bindfile(I)
myapp.bnd
myapp.sqc
Bind File
Source File
myapp.c
Modified
Source File

33. Precompile with Bindfile(II)
When the BINDFILE option is used, two outputs are produced.
Modified source file
Bind File: A package is not automatically created. A separate bind step must be run to produce a package.
db2 PREP myapp.sqc BINDFILE
BIND An Application Program
db2 BIND <bind file>

34. Privileges Required for Programming
Action Privileges Required
Precompile to bindfile CONNECT on DATABASE
Create a new package CONNECT on DATABASE
BINDADD on DATABASE
Privileges need to execute each static SQL statement
Modify a package CONNECT on DATABASE
BIND on package
Recreate a package CONNECT on DATABASE
Execute a package CONNECT on DATABASE
EXECUTE on package
Drop a package CONNECT on DATABASE
CONTROL on package or creator of package

35. Rebinding Implicit rebinding is automatic at next execution if
drop object referenced in package
drop primary key on table referenced in package
drop/add referential constraint on parent or child table referenced in package
revoke privilege required by binder to execute static SQL statement embedded in package

36. Explicit Rebinding
Rebinding - recreating a package for an application program that was previously bound
Why?
Take advantage of newly created index
Make use of updated statistics after executing the RUNSTATS command
Take control over when the rebinding occurs

37. Cursors in Embedded SQL

38. Objectives
How to use DECLARE, OPEN, FETCH, and CLOSE CURSOR statements to handle select criteria that may return multiple rows
UPDATE and DELETE rows identified by CURSORS

39. Processing Multiple Rows(I)
SELECT
SNAME DEPT
Claven cc
Natural cis
Yzchen csie
SNAME DEPT
FETCH
SNAME DEPT
Claven cc
Natural cis
Yzchen csie
Claven cc
SNAME DEPT

40. Processing Multiple Rows(II)
FETCH
SNAME DEPT
Claven cc
Natural cis
Yzchen csie
Natural
cis
SNAME DEPT
FETCH
SNAME DEPT
Claven cc
Natural cis
Yzchen csie
Yzchen
csie
SNAME DEPT

41. Processing Multiple Rows(III)
No method to determine the number of rows that will satisfy the WHERE clause of a SELECT statement in advance
Use CURSORS to process sets of data
The CURSOR is used to retrieve one row of data at a time
Each FETCH of the cursor retrieves the next row in the set of data that met the WHERE clause

42. SELECT with FETCH (I) Define a CURSOR Example
EXEC SQL DECLARE <Cursor Name> CURSOR FOR <Select Clause> ;
Example
EXEC SQL DECLARE k9 CURSOR FOR SELECT empno, lastname FROM TEMPL WHERE DEPT= :dept;

43. SELECT with FETCH(II) OPEN the CURSOR FETCH RESULT ROWS ONE AT A TIME
EXEC SQL OPEN <Cursor Name>;
EXEC SQL OPEN k9
Values assigned to host variables are relevant at OPEN
FETCH RESULT ROWS ONE AT A TIME
EXEC SQL FETCH <Cursor Name> INTO <host variables>
EXEC SQL FETCH k9 INTO :empno, :name;
Need a loop to fetch all result sets until SQLCODE 100 is returned

44. SELECT with FETCH (III)
CLOSE CURSOR when finished
EXEC SQL CLOSE <Cursor Name>;
EXEC SQL CLOSE k9;

45. DELETE Via A Cursor EXEC SQL DECLARE ce CURSOR FOR ...;
EXEC SQL OPEN ce;
while (SQLCODE != 100) { EXEC SQL FETCH ce INTO ....; EXEC SQL DELETE FROM TEMPL WHERE CURRENT OF ce; .... EXEC SQL CLOSE ce;

46. UPDATE Via A Cursor
EXEC SQL DECLARE cx CURSOR FOR SELECT empno, lastname FROM TEMPL WHERE deptno = :dpt FOR UPDATE OF lastname; EXEC SQL OPEN cx; EXEC SQL UPDATE TEMPL SET lastname = :newname WHERE CURRENT OF cx; .....

47. UPDATE/DELETE Via A Cursor
DECLARE CURSOR statement may not contain “FOR UPDATE OF”, nor may the cursor be used for “DELETE WHERE CURRENT OF”, if the SELECT statement contains:
GROUP BY
ORDER BY
DISTINCT
UNION, EXCEPT, INTERSECT
function
join
FOR FETCH ONLY

48. Privileges
Privileges convey the right to perform a specific action on a specific object.

49. Table and View Privileges
Control
ALTER
DELETE
INDEX
INSERT
REFERENCES
SELECT
UPDATE
View: Privileges on the underlying objects.
Create a View: SELECT and CONTROL
INSERT/UPDATE/DELETE

50. Index and Package Privileges
CONTROL Privilege
Package:
CONTROL
EXECUTE
BIND

51. GRANT
GRANT <privilege>|ALL ON [TABLE] <table> TO [USER] <user>|GROUP <group>|PUBLIC
GRANT CONTROL ON INDEX <index> TO [USER] <user>|GROUP <group>|PUBLIC
GRANT <privilege>|ALL ON PACKAGE <package> TO [USER] <user>|GROUP <group>|PUBLIC
Example:
GRANT SELECT, INSERT ON test.table1 TO t1, t2;
GRANT BIND, EXECUTE ON PACKAGE ap1 TO PUBLIC;

52. REVOKE
REVOKE <privilege>|ALL ON [TABLE] <table> FROM [USER] <user>|GROUP <group>|PUBLIC
REVOKE CONTROL ON INDEX <index> FROM [USER] <user>|GROUP <group>|PUBLIC
REVOKE <privilege>|ALL ON PACKAGE <package> FROM [USER] <user>|GROUP <group>|PUBLIC
Example:
REVOKE ALL PRIVILEGES ON table1 FROM USER freddy;
REVOKE CONTROL ON INDEX i1 FROM smith, jones;