SQL

SQL, or Structured Query Language, is a platform independent way of accessing databases. However, the version of SQL which runs on the AS/400, known as SQL400 or SQLDB2, does have syntax differences from other SQL dialects such as Microsoft SQL Server or Oracle, as well as DB2 on other platforms. Detractors of DB2 for i tend to point up these differences as deficiencies, but every vendor has differences that make each dialect somewhat incompatible.

Terminology

SQL Term	iSeries Term
TABLE	PHYSICAL FILE
ROW	RECORD
COLUMN	FIELD
INDEX	KEYED LOGICAL FILE ACCESS PATH
VIEW	NON-KEYED LOGICAL FILE
SCHEMA	LIBRARY COLLECTION
LOG	JOURNAL
ISOLATION LEVEL	COMMITMENT CONTROL LEVEL

Tips

SQL7008 error

&FILE in &LIBRARY not valid for operation.

-- Code 3 -- &FILE is not journaled, or you do not have authority to the journal. Files with an RI constraint action of CASCADE, SET NULL, or SET DEFAULT must be journaled to the same journal.

• Resolution: Use RUNSQLSTM with parameter COMMIT(*NONE)

SELECT *

For the sake of example, use two files, master and trans. We want to select all the columns in trans but only the name column from table master.

If using *SYS naming you can execute SELECT trans.*, name FROM trans JOIN master ON...

If using *SQL naming, we need to use a correlation name: SELECT t.*, name FROM trans t JOIN master ON...

RUNSQL command for ad-hoc SQL statements

"Partner TechTip: Blend SQL and RPGLE to Make Better Tools" by Kevin Forsythe

Another method is based on Query Management Query. Create the QMQRY as all substitution variables and populate them in CL. Midrange FAQ entry for the unfortunately named RUNSQLSTM.

Query Options File

IBM i allows one to alter the behaviour of the Query optimiser by use of a file called QAQQINI IBM supply a template in QSYS which you can copy into QUSRSYS and alter to suit your needs. If you want a custom options file, copy it into your own library and use the command CHGQRYA to tell the system where to find it. The system uses the one in QUSRSYS as a system-wide default.

On V5R4, using OLAP can mean having a good look at the value of IGNORE_DERIVED_INDEX. One may want to set it to YES in order to use a heritage database with OLAP.

• Adjust Default Query Optimizer Settings with QAQQINI Midrange Guru, Sept 2003.
• My Own Private QAQQINI MC Press Online, May 2001

See also

See also: SQL Primer and SOUNDEX

See also on Wikipedia: SQL