Informix and DB2 an
SQL Perspective
Informix and DB2 SQL
Bob Carts
Senior Data Engineer, SAIC
robert.m.carts@saic.com
Keith Gibert
Software Engineer, SAIC
myron.k.gibert.sr@saic.com
1-22-2004
Slide 2
Our Story – How We Spent our Summer Vacation

We were told to convert to DB2 version 8.1

No DB2 Experience or Training

Data Warehouse Application

900 GB of data

Using Informix XPS version 8.31

684 pieces of ETL code

ETL code SQL, KSH, PERL

No stored procedures or triggers
1-22-2004
Slide 3
Introduction

Certified Informix DBA (Bob)

Certified DB2 DBA (Bob)

WAIUG Board of Directors (Bob)

Work for SAIC (Science Applications International
Corporation)

Windows and UNIX (Solaris, IBM AIX, HP-UX)

IDS 7.31, 9.21, 9.3, XPS 8.31, DB2 8.1

Data Warehouse and OLTP Applications
1-22-2004
Slide 4
Scope of Presentation


Goal: To provide basic information on differences
between Informix and DB2 SQL to help you get started in
evaluating, planning or executing a conversion
Assumption:
 You

are familiar with Informix, dbaccess, SQL
Included:
 Some

basic SQL differences
Not Included:
 DBA Stuff,
Internals,Embedded SQL, Triggers and Stored
Procedures
1-22-2004
Slide 5
Some Things We Learned - Support



Make friends with DB2 Developers in Toronto because
the DB2 help desk does not answer SQL questions
DB2 SQL assistance is available for $
Informix Help Desk Does answer SQL questions
1-22-2004
Slide 6
Some Things We Learned – Documentation




DB2 documentation is on par or better than Informix
documentation (and Informix documentation is pretty
good!)
Improvements to the documentation are in the works
(adding examples)
Look at IBM.com, DB2 Technical Support, Product
Manuals
The manuals we use most:
 SQL reference Volumes
 Data
1 and 2
Movement Utilities Guide and Reference
1-22-2004
Slide 7
Some Things We Learned – Monitoring

Informix “onstat” commands make for easy monitoring

While monitoring tools are available in DB2, they can be
awkward

Onstat type monitoring commands are on the list to be
added to DB2 in a future release
1-22-2004
Slide 8
Some Things We Learned – Monitoring



Determine which processes are running:

INFORMIX: Onstat –g ses/sql/act/ath

DB2: list applications show detail
View a specific process:

INFORMIX: onstat –g ses <PID>

DB2: get snapshot for application agentid <PID>
Kill a process:

INFORMIX: onmode –z <PID>

DB2: force application ‘(PID)’ or force application all
1-22-2004
Slide 9
Some Things We Learned – Monitoring

Veiw the database configuration:
 INFORMIX:
onstat –c
 DB2:
get database configuration and/or get database managers
configuration (get db cfg / get db mgr cfg)

View available tablespace:
 INFORMIX:
 DB2:
onstat –d/-D/-t/-T
list tablespace show detail
1-22-2004
Slide 10
Interactive Access




DBACCESS – Psuedo GUI, Menu bar driven
DB2 CLP (command line processor) – A little clumsy, but
adequate. More like sybase or oracle interface
Getting Help
 Help
dbaccess cntl-w
 Help
? CLP Command
Connecting
 Db2
initially requires an explicit connect
 Informix
implicitly connects when using dbaccess
1-22-2004
Slide 11
DB2CLP

Several ways to execute commands
 db2
<command>
 Example:

db2 connect to mydb
You can also use interactive mode
db2 –t
Connect to mydb;
Select col1, col2
From mytable;
Quit;
1-22-2004
Slide 12
DB2CLP

You can execute OS commands within DB2 CLP
! Cp file1 file2

Get a list of databases:
List active databases;

Get a list of columns:
List tables [for schema <schemaname>;

Get the layout of a table:
Describe table <schemaname>.<tablename>;
1-22-2004
Slide 13
Calling from ksh Script
Dbaccess [dbname] <<EOF > stdout 2>stderror
Select bla bla bla;
EOF
 Db2 –tvl <logfilename> <<EOF >
Connect to [dbname];

Select bla bla bla
EOF
1-22-2004
Slide 14
A few little things…


Default Permissions

Informix: Public has permissions by default

DB2: public does not
Updating Statistics (different syntax)
Runstats on <schema>.<table> with distribution
And indexes all shrlevel change;

Code Comments

DB2 does support the dash dash for comments
However, they need to start in column #1 of a line
-- This works as a comment

somecol char(3)
-- this does not
1-22-2004
Slide 15
A few little things…

Don’t use double quotes in DB2 !
Select * from tabname where name = ‘Bob’

DB2 does not support Directives
1-22-2004
Slide 16
Datatypes



DB2 does not support implicit casting
Explicitly cast all data types in expressions
Example:
Create table bob.tabname (col1 integer,col2 char(10),col3 char(3))…
Insert into tabname values (null, ‘bob’, null) --informix
Insert into tabname values (cast(null as integer), ‘bob’, cast(null as
char))
1-22-2004
Slide 17
Limiting Number of Rows Returned/
Optimize for Number of Rows

Informix: Select first 100 ssn from people;
DB2:
Select ssn from people
Fetch first 100 rows only;

Optimize for a particular number of rows (db2 only)
Db2:
Select ssn from people
Optimize for 20 rows;
1-22-2004
Slide 18
Join Syntax


DB2 Outer join syntax is different than Informix
DB2 is reportedly ANSI standard and Informix is not
1-22-2004
Slide 19
Join Syntax
INFORMIX:
Select a.name, a.employ_num, b.program, c.ed_level
From employee a, training b, OUTER education c
Where a.employ_num = b.employ_num and
a.employ_num = c.employ_num and
b.program = ‘DB2101’
DB2: Select a.name, a.employ_num, b.program, c.ed_level
From employee a
INNER JOIN training b
on a.employ_num = b.employ_num
LEFT OUTER JOIN education c
on a.employ_num = c.employ_num
Where b.program = ‘DB2101’
1-22-2004
Slide 20
Group by

Can’t use “number” syntax
Group by 1,2,3….

Forced to make case statements, etc redundant
1-22-2004
Slide 21
Group by - INFORMIX
Select gender, state_of_birth,
Case when age > 19 and age < 31 then ‘Young’
when age > 30 and age < 46 then ‘middle aged’
when age > 46 then ‘Up there’
End category
From employee
Group by 1,2,3
1-22-2004
Slide 22
Group by – DB2
Select gender, state_of_birth,
Case when age > 19 and age < 31 then ‘Young’
when age > 30 and age < 46 then ‘middle aged’
when age > 46 then ‘Up there’
End case
From employee
Group by gender, state_of_birth,
Case when age > 19 and age < 31 then ‘Young’
when age > 30 and age < 46 then ‘middle aged’
when age > 46 then ‘Up there’
End case
1-22-2004
Slide 23
Having


Syntax available in DB2 and not Informix
Look for duplicate keys
select * from people_table where ssn in
(select ssn from people_table
group by ssn having count(*) > 1 );
1-22-2004
Slide 24
Alter Statements


Alter capabilities are limited in DB2
 Can’t
drop a column
 Can’t
change a datatype for a column
We of course used the alter – drop in our Informix Code!
1-22-2004
Slide 25
UnLogged Tables


Using Unlogged databases in Informix is straight forward
Using Unlogged tables in db2 version 7.2 is
 Awkward
 Temporary
 Dangerous
 Still


Possible
Db2 version 8.1 is less disastrous
Basic problem is auto rollback makes table permanently
unavailable, must recreate or restore
1-22-2004
Slide 26
UnLogged Tables

When creating a table must specify that logging can be turned off
Create table bob.xyz
(Col1 char(2))
In tablespace123 index in indexspace456
Not logged initially;

Must alter the table to temporarily turn logging off
Update command options using c off;
Alter table bob.xyz activate not logged initially;
Insert into bob.xyz …
Commit;

If anything goes wrong, boom no useable table!
1-22-2004
Slide 27
Utilities

DB2 has import, export, load utilities
 Load
is fastest way to get data into table
 Load can handle various delimiters or no delimiters
 You can replace or insert (append)
 Terminate or restart
 Example:
Load from /pathname/filename
Of del modified by coldel| keepblanks anyorder
Messages messagefile.msg
Temp files path /large_directory
Replace into bob.xyz;
1-22-2004
Slide 28
Utilities

Another load example:
load from strip.txt OF ASC
METHOD L (1 7,9 43,45 54,56 90,92 126,128 145,
147 148,150 160,268 277,336 336)
messages messagefile.msg
tempfiles path $WORKDIR
replace INTO bob.xyz NONRECOVERABLE;

Import is slow
1-22-2004
Slide 29
Utilities





Export has several differences from dbexport
By default numbers have a + and leading zeros
Character data is enclosed by double quotes
Character data is padded to full length
Example:
Export to filename.out
Of del modified by coldel| decplusblank
Select date_provided, rtrim(record_id) from tabname;

Used sed to strip out quotes and leading zeros
1-22-2004
Slide 30
Utilities


Getting the ddl
Informix: dbschema
Dbschema –d databasename outputfilename.out

DB2: db2look
Db2look –d databasename –e > outputfilename.out


Both have many options
Both have usage built in, just type command
1-22-2004
Slide 31
Error Messages

Both databases allow retrieval of error messages from the
command line
 INFORMIX:
finderr -217
 DB2:
db2 ? SQL0203
1-22-2004
Slide 32
Error Messages - INFORMIX
-217 Column column-name not found in any table in the query
(or SLV is undefined).
The name appears in the select list or WHERE clause of this query but is
not defined in a table and does not appear as a statement local variable
(SLV) definition. Check that the column name or SLV name and the names of
the selected tables are spelled as you intended.
If all names are spelled correctly, you are not using the right tables,
the database has been changed, or you have not defined the SLV. If the
name not found is a reference to a column, that column might have been
renamed or dropped. If the name not found represents an SLV and you
defined the SLV in the statement, make sure that the SLV definition
appears before all other references to that SLV name.
This error message can also appear during the execution of an ALTER TABLE
statement when the engine tries to update views that depend on the table.
1-22-2004
Slide 33
Error Messages – DB2
SQL0203NA reference to column "<name>" is ambiguous.
Explanation: The column "<name>" is used in the statement and there is more than one possible
column to which it could refer. This could be the result of:
two tables specified in a FROM clause that have columns with the same name
the ORDER BY clause refers to a name that applies to more than one column in the select list
a reference to a column from the subject table in a CREATE TRIGGER statement does not use
the correlation name to indicate if it refers to the old or new transition variable.
The column name needs further information to establish which of the possible table columns it is.
The statement cannot be processed.
User Response: Add a qualifier to the column name. The qualifier is the table name or correlation
name. A column may need to be renamed in the select list.
sqlcode: -203
sqlstate: 42702
1-22-2004
Slide 34
INFORMIX XPS (Version 8.x)




DB2 does not have the external table feature, must up
import, export and load utilities
DB2 requires explicit indexes to perform adequately
DB2 does not have the join update/batch update feature
(a subselect must be used)
DB2 does not support truncate command
1-22-2004
Slide 35
Summary

Support


Documentation

Limiting rows returned
Join Syntax

Monitoring

Group by

Interactive access

Having

Calling from ksh

Alter statements

Default permissions


Update Statistics

Unlogged tables
Utilities

Code comments

Error messages

Double quotes

XPS differences

Directives

Resources

Datatypes
1-22-2004
Slide 36
Resources

Db2 administration guide (book)

http://www.ibm.com/developerworks/db2/
 Online
tutorials geared for certification testing
 Porting Resources
 Bunch of other items
1-22-2004
Slide 37
Contact

Contact
robert.m.carts@saic.com,
myron.k.gibert.sr@saic.com
Presentation will be placed on WAIUG site:
www.iiug.org/~waiug
1-22-2004
Slide 38