Create or replace for SQL Tables

In previous posts I have given examples of using the CREATE OR REPLACE for all kinds of SQL objects: Views, Indexes, Functions, Triggers, Sequences, etc. One situation I have not mentioned is using this option when creating a Table. I know it sounds a bit scary to replace an existing Table that contains data. If I am going to do it I want to have the option to preserve the data or to delete it.

Creating a new table is as easy as:

01 CREATE TABLE MYLIB.TESTING_TABLE 02 FOR SYSTEM NAME "TESTTABLE" 03 ( 04 FIRST_COLUMN FOR "FIRST" VARCHAR(10) NOT NULL, 05 IDENTITY_COLUMN FOR "ID_COL" BIGINT 06 GENERATED ALWAYS AS IDENTITY 07 ) ; 08 INSERT INTO MYLIB.TESTTABLE (FIRST_COLUMN) 09 VALUES('FIRST'),('SECOND'),('THIRD') ;

Retrieving commands' defaults, CLOB-ing it

Last week I wrote about how to use an API to retrieve a command's defaults. I encountered a problem when the string returned by the API would be blank. I did not know what was causing this. Fortunately two people added comments to the post explaining the issue: if the string returned is longer than the size of the result variable blank is returned. I want to thank both of them for letting me know what was causing this problem.

Therefore, if I increased the size of the subfield in the API's result data structure I see the results for those commands I did not see before.

This caused another problem, as I could no longer use the field in the DDS file I had defined before. The maximum size of an alphanumeric field is 32,766 bytes, which proved too small for some of the commands I tested with. My first thought was to use a (SQL) DDL table instead, but the maximum size of a character column is one byte smaller than for the DDS alphanumeric field, 32,765. As these XML strings can be extremely long I will need to insert these into a CLOB, Character Large Object, column as this can contain up to 2,147,483,647 bytes, way more than I could ever need.

My SQL DDL table looks like:

Retrieving commands' defaults

I wanted to retrieve the defaults for a number of IBM commands, so I could compare them to those in another IBM i partition. I found an API, QCDRCMDD, would give me a XML string of the command's definition, that I could then write to a file. This file could then be transferred to the other partition and used when comparing the two sets of commands' information.

The output file, OUTFILE, would contain one field, for the XML string, but would need to big enough to contain the longest possible XML string. My guess is that a field of 10,000 characters would be long enough to cover most commands.

01 A R OUTFILER 02 A FIELD 10000A

Using Navigator for i for SQL index suggestions

I have been playing with the new release of Access Client Solutions, ACS 1.1.8.5, and have been impressed with it. I have found Navigator for i a bit faster so thought it was time to revisit one of the coolest features included in it, the Db2 for i index advisor.

I have written about using the index advisor using the old Client Access Operation Navigator before. The ACS version of the index advisor is so much easier to use I wanted to encourage you to look at it.

When you access a table or file using SQL the Db2 engine determines the best access path to use to extract the data requested. If there is not a suitable existing access path it will build a temporary one. When it does, it makes an addition to the index advisor table with the suggested key, or if there is already a row it increments the "times used" counter. I can use the index advisor to see which indexes are suggested. If there is a suggested index that has been used many, many times then I will build it to make the SQL faster, as it no longer has to build the temporary access path.

Prestart jobs' information using SQL

What are prestart jobs? They are batch jobs that run to allow programs on remote systems to communicate with the IBM i partition. They use prestart job entries that are found in the subsystem descriptions of the subsystems in which they run.

Previously the only way you could list the information about prestart jobs was to use the Display Subsystem Description command, DSPSBSD, one subsystem at a time, or the Display Active Prestart Job command, DSPACTPJ, one job at a time. The latest Technology Refreshes, IBM i 7.4 TR2 and 7.3 TR8, introduced the following to Db2:

• PRESTART_JOB_INFO View
• PRESTART_JOB_STATISTICS Table function

Both of these are found in the QSYS2 library.