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Paul TuohyComCon System i Developer5, Oakton Court, BallybrackCo. DublinIreland

Phone: +353 1 282 6230e-Mail: [email protected]: www.systemideveloper.com www.ComConAdvisor.com

ComConProducers of the RPG & DB2 Summit

Embedded SQL in RPG

ComConPaul Tuohy

Paul Tuohy has worked in the development of IBM Midrange applications since the �70s. He has been IT manager for Kodak Ireland Ltd. and Technical Director of Precision Software Ltd. and is currently CEO of ComCon, a midrange consultancy company based in Dublin, Ireland. He has been teaching and lecturing since the mid-�80s.

Paul is the author of "Re-engineering RPG Legacy Applications�, �The Programmers Guide to iSeries Navigator� and the self teach course �iSeries Navigator for Programmers�. He writes regular articles for many publications and is one of the quoted industry experts in the IBM Redbook "Who knew you could do that with RPG IV?".

Paul is one of the co-founders of System i Developer and is also an award winning speaker who speaks regularly at US Common and other conferences throughout the world.

© ComCon and System i Developer, LLC 2006-2011 -1-

ComConDisclaimer

This presentation may contain small code examples that are furnished as simple examples to provide an illustration. These examples have not been thoroughly tested under all conditions. We therefore, cannot guarantee or imply reliability, serviceability, or function of these programs.

All code examples contained herein are provided to you "as is". THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY DISCLAIMED.

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ComConAgenda

Syntax and rules for embedding SQL into programs

Using SQL cursors for processing individual rows in a set

Error detection and handling

Dynamic SQL introduction

Tips and Performance


ComConUsing SQL on i5OS (OS/400)

Interactive SQL - Use iSeries Navigator

Targeted primarily to programmers

Interactive SQL - Use STRSQL command

Targeted primarily to programmers

Embedded SQL - Put into High Level Language (HLL)

Such as RPG or COBOL

Query Manager - Report Formatter

Targeted primarily to end users

An alternative to Query

SQL Stored Procedures and SQL Triggers

Enforce business rules using SQL-based logic

ComConRun SQL Scripts


03/11/11 7

Run SQL Scripts (from the context menu on the machine id) is the equivalent of STRSQL - but you do not need the SQL development kit.

End each SQL statement with a semi colon.

More then one SQL statement may be run at a time.

Sample SQL statements are available in the drop down box.

The basic SQL statements may be prompted.

ComConTypes of SQL Statements

Data Manipulation Language (DML)

SELECT - retrieves data; one row or multiple

UPDATE - updates one row or multiple

DELETE - deletes one row or multiple

INSERT - adds one row or multiple

Data Definition Language (DDL)

CREATE - creates schemas, tables, views, etc.

DROP - deletes schemas, tables, views, etc.

ALTER - change the format or attributes of a table

Data Control Language (DCL)

GRANT & REVOKE - manages authorities to DB objects

Programming Statements

DESCRIBE, PREPARE - used for dynamic embedded SQL

Logic control statements for SQL procedures, triggers and functions


ComCon

Different names for what we already have

But the names we use are important

Guess which terminology the rest of the world uses?

Please, please, please start to use the SQL terminology

Native SQL

Library Schema or Collection

Physical File Table

Keyed Logical Index

Non-Keyed Logical View

Record Row

Field Column

Journal Log

SQL Terminology

ComConEmbedded SQL

Why embed SQL in programs?

Perform dynamic selection functions- ala OPNQRYF, except more flexible

Perform set-at-a-time functions under program control

Even to replace HLL I/O operations- e.g., READ, WRITE, UPDATE, CHAIN

What can be embedded?

Most common use is for SQL DML statements - SELECT, UPDATE, DELETE, INSERT

Even DDL statements- such as CREATE TABLE, etc.

Program control statements

e.g., DECLARE CURSOR, OPEN, CLOSE, FETCH, COMMIT, ROLLBACK


ComConSQL Pre-Compile for Embedded SQL

SQL is pre-compiled

Syntax check

Xref host variables

Converts SQL statements to RPG

Inserts required SQL declarations

Optionally call RPG compiler to include /COPY directives (more later)

Original SourceMember

Original SourceMember

*PGM*PGM

Modified SourceMember

ProcessedSQL

Statements

(temporary)

Modified SourceMember

ProcessedSQL

Statements

(temporary)

ProgramProgram

Access PlanAccess Plan

Pre-CompilePre-CompilePre-Compile CompileCompile

ComConRules: Embedding SQL in RPG Code (to V5R2)

All SQL statements must be coded on a C spec

SQL statements begin with /EXEC SQL in positions 7-15

with the slash in position 7

... and end with /END-EXEC in positions 7-15

You can enter SQL statements on the same line as /EXEC SQL

However, /END-EXEC must be on a separate line

All SQL statements must have C+ in positions 6-7

D getEmployee S 6a

D name S 15a

D deptno S 3a

C/EXEC SQL

C+ SELECT lastName, workDept

C+ INTO :name, :deptno

C+ FROM employee

C+ WHERE empno = :getEmployee

C/END-EXEC

D getEmployee S 6a

D name S 15a

D deptno S 3a

C/EXEC SQL

C+ SELECT lastName, workDept

C+ INTO :name, :deptno

C+ FROM employee

C+ WHERE empno = :getEmployee

C/END-EXEC

No F Spec RequiredNo F Spec Required


ComConSQL in Free Format (V5R3+)

SQL statements may now be coded directly in /Free format

Introduced in V5R4

PTFs SI23384, SI25532, and SI25763 required for V5R3

SQL statements begin with EXEC SQL

End the complete SQL statement with a semi colon

D getEmployee S 6a

D name S 15a

D deptno S 3a

/free

getEmployee = '00010';

exec SQL

select lastName, workDept

into :name, :deptno

from employee

where empno = :getEmployee ;

dsply Name;

D getEmployee S 6a

D name S 15a

D deptno S 3a

/free


exec SQL


into :name, :deptno

from employee


dsply Name;

ComConSQL Host Variables

Host variables identify program fields used in static SQL statements

Host variable names are preceded by a colon

as in :host-variable-name

Host variables must be defined somewhere in the program

Typically in the D specs or in a display file

No F spec is used for database files accessed with SQL statements

D getEmployee S 6a

D name S 15a

D deptno S 3a

/free


exec SQL


into :name, :deptno

from employee


dsply Name;

D getEmployee S 6a

D name S 15a

D deptno S 3a

/free


exec SQL


into :name, :deptno

from employee


dsply Name;


ComConSELECT INTO

SELECT INTO SQL Statement is used to retrieve a single record from the database

If your statement returns more than 1 row, you must use another form of SELECT - which we will discuss later

D employeeNo S 6a

D lastName S 15a

D salary S 9p 2

exec SQL

select empNo, lastName, salary

into :employeeNo,:lastName,:salary

from employee

where empNo = '000010';

D employeeNo S 6a

D lastName S 15a

D salary S 9p 2

exec SQL


into :employeeNo,:lastName,:salary

from employee

where empNo = '000010';

ComConInserts, Updates and Deletes

SQL inserts, updates and deletes can be embedded as well

Extremely powerful

But - let the user beware!

exec SQL

delete from employee

where workDept = 'E21';

exec SQL

delete from employee


exec SQL

update employee

set salary = salary + (salary * .10)


exec SQL

update employee

set salary = salary + (salary * .10)


exec SQL

insert into employee (empno, fName, lastName, workDept)

values(:employeeNo, :first, :last, 'E21');

exec SQL

insert into employee (empno, fName, lastName, workDept)

values(:employeeNo, :first, :last, 'E21');


ComConUsing Structures in SQL

Host structures are groups of variables

Data structures in RPG

Structures can be used in SQL statements

Replaces list of variables

DS subfields must contain the correct number, type and sequence for SELECT columns

D employeeInfo DS

D employeeNo 6a

D lastName 15a

D salary 9p 2

D getEmployee S 6a

/free

exec SQL


into :employeeInfo

from employee

where empNo = :getEmployee;

D employeeInfo DS

D employeeNo 6a

D lastName 15a

D salary 9p 2

D getEmployee S 6a

/free

exec SQL


into :employeeInfo

from employee


ComConExternal Data Structures

Only if all columns are required

Use a SELECT * request

Declare an externally described Data Structure

Subfields will be brought in to match all the fields in the record format

No level checking- Up to you to re-compile if format changes

Watch out for date/time fields- May require compile or SET options

D employeeData E DS extName(employee)

D getEmployee S 6a

exec SQL

select *

into :employeeData

from employee


D employeeData E DS extName(employee)

D getEmployee S 6a

exec SQL

select *

into :employeeData

from employee



ComConResult Set

A Result Set is:-

A group of rows that are derived as a result of an SQL query

The answer to your SQL question

Made up of rows and columns

select deptno, deptname from department where admrdept = 'D01';select deptno, deptname from department where admrdept = 'D01';

ComConSelecting & Processing Multiple Rows

Steps to access multiple rows:

Declare cursor

Open cursor

Fetch a row (record)

Process row (UPDATE, INSERT, etc)

IF NOT last row: loop to Fetch

Close cursor

Just like any sequential read!


ComConDECLARE CURSOR statement

Similar in function to HLL file declarations (F-specs)

No processing actually takes place - just definition

Host variables may be included in the statement

Created using an embedded SELECT command

most SELECT clauses may be used - ORDER BY, GROUP BY, etc

A cursor must be declared before being referenced

exec SQL

declare empCursor cursor for


from eEmployee

where workDept = :dept;

exec SQL



from eEmployee

where workDept = :dept;

ComConDECLARE CURSOR - more clauses

By default, all columns may be updated or deleted

FOR READ ONLY - specifies no updating/deleting allowed- Improves performance- Rows not locked for update

FOR UPDATE OF - lists the columns that are to be updated- columns listed in an ORDER BY clause may NOT be listed in FOR UPDATE OF clause

Considerations:

FOR READ ONLY - may improve performance; better documentation

FOR UPDATE OF - security; may improve performance

exec SQL



from eEmployee

where workDept = :dept

for read only ;

exec SQL



from eEmployee


for read only ;


ComConOPEN statement

Actually executes the SQL Select statement

Builds the access path if necessary

Successful Open places the file cursor before the first row of the result set

Cursor must be closed before it can be opened

Syntax: OPEN cursor-name

exec SQL

open empCursor ;

exec SQL

open empCursor ;

ComConFETCH statement

Bring rows into the program

One at a time for processing

Fields placed into host variables

one for one with fields in SELECT

exec SQL

fetch next from empCursor

into :employeeNo,:lastName,:salary ;

exec SQL




ComConProcess FETCHed Row

To Update or Delete the fetched row

Use Where Current of Clause on Update/Delete statement

Can only be done after a successful Fetch

exec SQL

update employee

set salary = salary + :raise

where current of empCursor;

exec SQL

update employee

set salary = salary + :raise

where current of empCursor;

ComConAlternatives with FETCH

Alternatives to Next processing:

must define the cursor as a scrollable cursor in the declare statement

exec SQL

declare empCursor scroll cursor for


from employee


order by empNo ;

exec SQL

fetch prior from empCursor

into :employeeNo,:lastName,:salary;

exec SQL

declare empCursor scroll cursor for


from employee


order by empNo ;

exec SQL

fetch prior from empCursor

into :employeeNo,:lastName,:salary;


ComConFetch Options

Alternatives to Next processing

Fetch keyword

Keyword Positions Cursor

next On the next row after the current row

prior On the row before the current row

first On the first row

last On the last row

before Before the first row - must not use INTO

after After the last row - must not use INTO

current On the current row (no change in position)

relative n n < -1 Positions to nth row before current n = -1 Same as Prior keywordn = 0 Same as Current keyword n = 1 Same as Next keywordn > 1 Positions to nth row after current

ComConClose Statement

Close the cursor

Cursor must be opened in order to be closed

Cursor will be closed if

job end

activation group ends

program ends

modules ends

commit or rollback without a 'with hold' clause

error handling...

exec SQL

close empCursor ;

exec SQL

close empCursor ;


ComConPutting it all together�

Sequential read of a file

exec SQL



from eEmployee


for read only ;

exec SQL

open empCursor ;

exec SQL



doW (SQLCode >= 0 and SQLCode <> 100); // More in a moment

// Do Your stuff here

exec SQL



endDo;

exec SQL

close empCursor ;

exec SQL



from eEmployee


for read only ;

exec SQL

open empCursor ;

exec SQL



doW (SQLCode >= 0 and SQLCode <> 100); // More in a moment

// Do Your stuff here

exec SQL



endDo;

exec SQL

close empCursor ;

ComConError Detection and Handling (1 of 3)

Status always returned in the code

both successful and unsuccessful statements

Programmer must check return codes within program

SQL Communications Area (SQLCA)

contains feedback information

must be included in all SQL programs

RPG includes SQLCA automatically

other languages must have specific INCLUDE



SQL Communications Area (SQLCA)

SQLCAID Char(8) Structure identifying literal: "SQLCA"

SQLCABC Integer Length of SQLCA

SQLCode Integer Return code

SQLErrML SmallInt Length of SQLErrMC

SQLErrMC Char(70) Message Replacement text

SQLErrP Char(8) Product ID literal: "QSQ" for DB2 UDB

SQLErrD Array of Integers

SQLErrD(1) - last 4 characters of CPF or other escape message SQLErrD(2) - last 4 characters of CPF or other diagnostic message SQLErrD(3) - for Fetch, Insert, Update or Delete, number of rows retrieved or updated SQLErrD(4) - for Prepare, relative number indicating resources required for execution SQLErrD(5) - for multiple-row Fetch, contains 100 if last available row is fetched; for Delete, number of rows affected by referential constraints; for Connect or Set Connection, contains -1 if unconnected, 0 if local and 1 if connection is remote SQLErrD(6) - when SQLCode is 0, contains SQL completion message id


SQL Communications Area (SQLCA) - continued

SQLWarn Char(11) Set of 11 warning indicators; each is blank, W, or N

SQLWarn0 Char(1) Blank if all other SQLWARNx warning indicators are blank W if any warning indicator contains W or N

SQLWarn1 Char(1) W if a string column was truncated when assigned to host variable

SQLWarn2 Char(1) W if null values were eliminated from a function

SQLWarn3 Char(1) W if number of columns is larger than number of host variables

SQLWarn4 Char(1) W if prepared Update or Delete statement has no a Where clause

SQLWarn5 Char(1) Reserved

SQLWarn6 Char(1) W if date arithmetic results in end-of-month adjustment


SQLWarn8 Char(1) W if result of character conversion contains the substitution character


SQLWarnA Char(1) Reserved

SQLState Char(5) Return code; "00000" if no error or warning


ComConSQLCA Data Structure (1 of 2)

D SQLCA DS

D SQLCAID 8A INZ(X'000000000000000

D SQLAID 8A OVERLAY(SQLCAID)

D SQLCABC 10I 0

D SQLABC 9B 0 OVERLAY(SQLCABC)

D SQLCODE 10I 0

D SQLCOD 9B 0 OVERLAY(SQLCODE)

D SQLERRML 5I 0

D SQLERL 4B 0 OVERLAY(SQLERRML)

D SQLERRMC 70A

D SQLERM 70A OVERLAY(SQLERRMC)

D SQLERRP 8A

D SQLERP 8A OVERLAY(SQLERRP)

D SQLERR 24A

D SQLER1 9B 0 OVERLAY(SQLERR:*NEXT)






D SQLERRD 10I 0 DIM(6) OVERLAY(SQLERR)

D SQLCA DS

D SQLCAID 8A INZ(X'000000000000000

D SQLAID 8A OVERLAY(SQLCAID)

D SQLCABC 10I 0

D SQLABC 9B 0 OVERLAY(SQLCABC)

D SQLCODE 10I 0

D SQLCOD 9B 0 OVERLAY(SQLCODE)

D SQLERRML 5I 0

D SQLERL 4B 0 OVERLAY(SQLERRML)

D SQLERRMC 70A

D SQLERM 70A OVERLAY(SQLERRMC)

D SQLERRP 8A

D SQLERP 8A OVERLAY(SQLERRP)

D SQLERR 24A







D SQLERRD 10I 0 DIM(6) OVERLAY(SQLERR)

SQLCA is automatically inserted by pre-compiler

ComConSQLCA Data Structure (2 of 2)

D SQLWRN 11A

D SQLWN0 1A OVERLAY(SQLWRN:*NEXT)










D SQLWNA 1A OVERLAY(SQLWRN:*NEXT)

D SQLWARN 1A DIM(11) OVERLAY(SQLWRN)

D SQLSTATE 5A

D SQLSTT 5A OVERLAY(SQLSTATE)

D SQLWRN 11A











D SQLWNA 1A OVERLAY(SQLWRN:*NEXT)

D SQLWARN 1A DIM(11) OVERLAY(SQLWRN)

D SQLSTATE 5A

D SQLSTT 5A OVERLAY(SQLSTATE)

Note double definition of names

Allows for programs converted from RPG III- e.g. SQLCODE and SQLCOD

SQLCA is not the only set of definitions inserted by the pre-compiler

Other definitions are dependent on the actual SQL statements

All inserted names start with the characters SQL

Try to refrain from naming any variables starting with SQL


ComConSQLCODE Error Handling

SQLCODE contains return code

= 0 Successful statement execution

> 0 Successful, with warning condition

< 0 Unsuccessful - statement failed

SQLCODE value indicates exact error or condition

e.g.. 100 = Row not found (or end of file)

e.g.. -552 = Not authorized to object

SQLCODE values have corresponding messages

e.g.. SQL0100 = Row not found

e.g.. SQL0552 = Not authorized to &1

Many SQL programmers also check SQLWN0

A few warning conditions do not return > 0 SQLCODE value- e.g., If SQLCOD > 0 or SQLWN0 <> *Blank

ComConSQLCODE and Messages

Most SQLCODE values map to message IDs in QSQLMSG message file

MSGID is SQxxxxx where xxxxx is derived with the following rules:- Calculate the absolute value of the SQLCODE value- Zero-fill the result with leading zeros to construct a 5-digit number

- If the first digit in this number is 0, replace it with the letter 'L'

For example, SQLCODE value of -151 = message ID SQL0151

SQLCODE value of -30090 = message ID SQ30090

Use DSPMSGD RANGE(messageId) MSGF(QSQLMSG) to quickly find meanings of SQLCODE values


ComConSQLCODE vs. SQLSTATE (1 of 2)

SQLCODE values vary by platform

By contrast, SQLSTATE values are standard across platforms

However, SQLCODE is most widely used, especially for individual statements

SQLCODE is a deprecated function in current SQL standard

"Deprecated" means function replaced with a newer method- i.e SQLSTATE

Use of deprecated functions is typically discouraged

DB2 UDB for i plans to continue to support SQLCODE for the foreseeable future

Condition SQLCODE SQLSTATE Class(1st 2 positions)

Successful 0 00'

Warning >0 01'

End of Data Row not found

100 02'

Error <0 >='03'

ComConSQLCODE vs. SQLSTATE (2 of 2)

exec SQL

select lastName into :name

from employee

where empNo = :number;

select;

when SQLCode < 0;

// Bad Error

when SQLCode = 100;

// No More Rows

when ( SQLCode > 0

Or SQLWarn0 <> *Blank );

// Warning Error

other;

// Process Row

endSL;

exec SQL


from employee


select;

when SQLCode < 0;

// Bad Error

when SQLCode = 100;

// No More Rows

when ( SQLCode > 0

Or SQLWarn0 <> *Blank );

// Warning Error

other;

// Process Row

endSL;

exec SQL


from employee


select;

when %subSt(SQLStt:1:2) >= '03';

// Bad Error

when %subSt(SQLStt:1:2) = '02';

// No More Rows


// Warning Error

other;

// Process Row

endSL;

exec SQL


from employee


select;

when %subSt(SQLStt:1:2) >= '03';

// Bad Error


// No More Rows


// Warning Error

other;

// Process Row

endSL;


ComConFetch Multiple Rows

D listGroups DS dim(1000)

D group 5a

D description 50a

D numberOfRows S 10i 0 inz(%elem(listGroups))

exec SQL

declare C1 scroll cursor for

select a.group, descript

from groups a inner join sessions b

on a.group = b.group

order by 1

for read only;

exec SQL

open C1;

exec SQL

fetch first from C1 for :numberOfRows rows into :listGroups ;

rowsReturned = SQLErrd(3);


D group 5a

D description 50a

D numberOfRows S 10i 0 inz(%elem(listGroups))

exec SQL

declare C1 scroll cursor for

select a.group, descript

from groups a inner join sessions b

on a.group = b.group

order by 1

for read only;

exec SQL

open C1;

exec SQL

fetch first from C1 for :numberOfRows rows into :listGroups ;

rowsReturned = SQLErrd(3);

Fetch multiple rows with a single Fetch

Use a data structure array- Older methods use a more cumbersome multiple occurrence data structure

Number of rows returned in SQLERRD(3)

ComConBlocked INSERT

Multiple elements from a host structure are inserted into a table

Program variable may be used to set the number of records to be inserted

Executes as if n INSERT statements had been issued - but with improved performance


D group 5a

D description 50a

D numberOfRows S 10i 0

exec SQL

insert into Employee

:numberOfRows rows

values (listGroups) ;


D group 5a

D description 50a

D numberOfRows S 10i 0

exec SQL

insert into Employee

:numberOfRows rows

values (listGroups) ;


ComConCRTSQLRPGI

Use CRTSQLRPGI to create programs and modules

OBJTYPE � Compile type (*PGM, *SRVPGM, *MODULE)- Can be used to create single module service program

Not two separate commands

/COPY directives not included automatically

Must specify RPGPPOPT(*LVL1) or RPGPPOPT(*LVL2) on compile

Watch out for some of the other compile parameters

COMMIT � Commitment Control (More later)

OPTION � Pre-compiler options (*SYS, *SQL)

INCLUDE � Include file

CLOSQLCSR � Close SQL Cursor

DATFMT � Date Format

But there is an alternative for some of the compile parameters�

03/11/11 42

The CRTSQLRPGI command may be used to create *MODULE, *PGM or *SRVPGM objects based on the value specified for the OBJTYPE parameter.

RPGPPOPT(*LVL1) means that /COPY directives and conditional compilation directives are processed - RPGPPOPT(*LVL1) is the same as *LVL1 with the addition of /INCLUDE directives being processed.

Other compiler directives to watch out for are:� COMMIT � We will discuss later.

� OPTION � Specify whether system (*SYS, the default) or *SQL (SQL) notation/naming convention is used in embedded SQL statements. This si more then simply using a dot or a slash notation on qualified names - *SYS means that the jobs library list is taken into account whereas *SQL assumes all tables are in a single schema (library) and, unless changed, it is assumed that the name of the default schema is the same as user profile for the calling job. OPTION is also used to set other compile options.

� INCLUDE � specifies the source physical file to be used for SQL Include directives (not to be confused with RPG directives)

� CLOSSQLCSR � specifies when an open cursor should be implicitly closed � end of module or end of activation group.

� DATFMT � specifies the date format to be used with date fields in SQL statements. Any date fields used as host variables must correspond to this format.


ComConSET OPTION

Some compile options can be set using a SET statement

Much like compile options in the H spec

SET OPTION keyword = value- COMMIT � Commitment control

- NAMING � SQL naming convention

- DATFMT/DATSEP � Date format and separator- TIMFMT/TIMSEP � Time format and separator

- DBGVIEW � Debugging View

Consider a standard SET OPTION statement in an include (copy) member

DBGVIEW may only specify a value of *NONE or *SOURCE

But *SOURCE actually results in three source views being available- SQL Root Source view

- SQL Output view (output from SQL pre-compiler)

- Listing view

exec SQL

set option commit = *NONE

datFmt = *ISO

datSep = '-'

naming = *SQL;

exec SQL

set option commit = *NONE

datFmt = *ISO

datSep = '-'

naming = *SQL;

ComConSQL and Commitment Control

The default on compiles is Commit *CHG

This means:

If files are not journaled, programs will abnormally terminate whenever you attempt to use any SQL on those files

If your files are journaled, you will have uncommitted transactions unless you remember to explicitly commit them

If your shop does not normally use commitment control, consider using Commit *NONE on your compile commands

Or use SET OPTION COMMIT = *NONE


ComConStatic and Dynamic SQL

Static SQL

SQL Statements known at compile time

Better Performance

Dynamic SQL

SQL Statements build during program execution

Greater Flexibility

Dynamic SQL provides a different way to use SQL

SQL statements are not predefined in program- Dynamically created on the fly as part of program logic

SQL Precompiler cannot fully process dynamically created SQL statements- PREPARE statement is used in program logic to compile dynamically created SQL

statements at run time

Simple dynamic SQL statement process:- Build SQL statement in a character variable

- PREPARE the SQL statement- EXECUTE the SQL statement

ComConWhere to use Dynamic SQL

Report programs with user run time selection for

Files

Fields

Record selection criteria

Sorting

SQL built in functions

Whenever the exact syntax of an SQL statement cannot be determined beforehand

Dynamic SQL can be resource intensive

A dynamic SQL statement has to be parsed (interpreted) and executed at run time

Negative performance impact

Use dynamic SQL only when necessary


ComConDynamic SQL � Example 1

Delete all employees in a department or delete a single employee row

Construct statement as string

PREPARE the statement- Apply a name to the prepared statement

- Check of SQLCODE to ensure statement is correct

EXECUTE the name defined on the PREPARE

if deleteDepartment;

condition = 'workDept = ''' + inputValue + '''' ;

else ;

condition = 'empNo = ''' + inputValue + '''' ;;

endIf;

mySQLStatement = 'delete from employee where ' + condition;

exec SQL

prepare dynamicSQL

from :mySQLStatement;

if (SQLCode = 0);

exec SQL

execute dynamicSQL

endIf;


condition = 'workDept = ''' + inputValue + '''' ;

else ;

condition = 'empNo = ''' + inputValue + '''' ;;

endIf;


exec SQL

prepare dynamicSQL


if (SQLCode = 0);

exec SQL

execute dynamicSQL

endIf;

ComConParameter Markers in Dynamic SQL

Dynamic SQL statements cannot contain host variables

e.g. :employeeNo

Parameter markers are placed in embedded SQL statements

Indicated by ?

Used to dynamically insert host variable data for predicate values and/or column assignments

Multiple markers and values can be assigned

Values are assigned to markers when the statement is executed- Example on next chart

mySQLStatement = 'delete from employee where empNo = ?' mySQLStatement = 'delete from employee where empNo = ?'


ComConDynamic SQL � Example Again


Construct statement as string- Place ? for any replacement value

PREPARE the statement- Apply a name to the prepared statement

- Check of SQLCODE to ensure statement is correct

EXECUTE the name defined on the PREPARE- Provide replacement values here


condition = 'workDept = ?' ;

else ;

condition = 'empNo = ?';

endIf;


exec SQL

prepare dynamicSQL


if (SQLCode = 0);

exec SQL

execute dynamicSQL using :inputValue;

endIf;



else ;


endIf;


exec SQL

prepare dynamicSQL


if (SQLCode = 0);

exec SQL

execute dynamicSQL using :inputValue;

endIf;

ComConDynamic SQL Using a Cursor


Construct the string and PREPARE the statement

DECLARE the cursor using the name defined on the PREPARE- Assign a cursor name

OPEN the cursor- Using the cursor name defined on the DECLARE

- Provide replacement values here



else ;


endIf;

mySQLStatement = 'select * from employee where ' + condition;

exec SQL

PREPARE dynamicSQL from :mySQLStatement;

if (SQLCode = 0);

exec SQL

declare empCursor cursor for dynamicSQL;

exec SQL

open empCursor using :inputValue;

endIf;



else ;


endIf;

mySQLStatement = 'select * from employee where ' + condition;

exec SQL

PREPARE dynamicSQL from :mySQLStatement;

if (SQLCode = 0);

exec SQL

declare empCursor cursor for dynamicSQL;

exec SQL

open empCursor using :inputValue;

endIf;


ComCon�True� Embedded SQL

exec SQL

declare C1 cursor For

With T1 as (select day, sequence, room, session, id as forId

from schedule left outer join speakers

on speaker = id ),

T2 as (select day, sequence, room, a.session, shorttitle,

coalesce(forId, speakerOwn) as speaker

from T1 a inner join sessions b

on a.session = b.session)

select daynum, Dayname, showseq, a.type, fromtotime, title,

room, c.session, c.shorttitle, name, fromtime, fullDay,

allowrpt

from agendav1 a inner join daynums b

on a.day = b.day

left outer join T2 c

on a.day = c.day and

a.sequence = c.sequence

left outer join speakers d

on c.Speaker = d.Id

left outer join sessions e

on c.session = e.session

where dayNum > 1 and

(a.type <> 'E' or (a.type = 'E' and IncAttSel = 'Y'))

order by 1, 3 for read only;

exec SQL

declare C1 cursor For

With T1 as (select day, sequence, room, session, id as forId

from schedule left outer join speakers

on speaker = id ),

T2 as (select day, sequence, room, a.session, shorttitle,

coalesce(forId, speakerOwn) as speaker

from T1 a inner join sessions b

on a.session = b.session)

select daynum, Dayname, showseq, a.type, fromtotime, title,

room, c.session, c.shorttitle, name, fromtime, fullDay,

allowrpt

from agendav1 a inner join daynums b

on a.day = b.day

left outer join T2 c

on a.day = c.day and

a.sequence = c.sequence

left outer join speakers d

on c.Speaker = d.Id

left outer join sessions e

on c.session = e.session

where dayNum > 1 and

(a.type <> 'E' or (a.type = 'E' and IncAttSel = 'Y'))

order by 1, 3 for read only;

ComConEmbedded SQL Tips

/COPY and /INCLUDE directives not included automatically

Must specify RPGPPOPT(*LVL1) or RPGPPOPT(*LVL2) on compile

SQL precompile step happens before RPG compile

If SQL syntax or semantic error occurs, no "typical" compile source listing available

Can be very difficult to work through problems at this stage

Try removing "SQL" from member type and compile "normally"

Compile will fail, but you can see results of externally described structures, COPYs, etc.

When using ILE source view debugger

ILE SQL program compiles automatically generate 3 different views with DBGVIEW(*SOURCE)

To help diagnose run-time problems

Look in your job log after running the SQL program

Messages there often help diagnose problems

Put your job in debug mode before running SQL program, then look in your job log- Additional messages are put in job log when in debug mode which can be helpful in

diagnosing SQL performance problems

To really hunt down performance problems, use Visual Explain in Run SQL Scripts


ComConPerformance Tips

Test statements in Run SQL Scripts before embedding them

Copy/Paste into RSE

SQL uses two basic ways to retrieve data

Dataspace scan or arrival sequence - Generally used when MORE than 20% of records will be selected

Index based or keyed access - Generally used when LESS than 20% of records will be selected

Performance can improve significantly if SQL can use an index

Create indexes for - columns frequently referenced in WHERE, GROUP BY and ORDER BY clauses- Fields that are frequently used to join tables

Where possible, make use of

Multiple Row FETCH

Blocked Insert

ComConPerformance Analysis Tools

PRTSQLINF

Prints information about the embedded SQL statements in a program, SQL package or service program

- SQL statements, Access plans, List of command parameters used by pre-compiler

STRDBMON

Or Database Monitor in Navigator

Predictive Query Governor

CHGQRYA command

TRCJOB

Visual Explain

Option in Run SQL Scripts in Navigator


ComConSummary

Practical, effective solution for applications requiring complex data retrieval

Very flexible, functional application development tool

embedded in a HLL program

or entered interactively

Portability to other relational databases

Easy report writing with programmable flexibility

Similarity across many relational databases

ComConBy the Speaker

�Re-Engineering RPG Legacy Applications�

ISBN 1-58347-006-9

�The Programmers Guide to iSeries Navigator�

ISBN 1-58347-047-6

www.mcpressonline.com

www.midrange.com

www.amazon.com

etc.

iSeries Navigator for Programmers

A self teach course

www.lab400.com

Article links at

www.comconadvisor.com


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