[GRASS-user] GRASS64 sql 'where' statement character/array limit?

GRASS GRASS user
1

Greetings all,

I am a new listserver member with a grass64 problem. I am hoping somebody can help me out:

I have a batch script that uses ps.map plot to select and plot areas from a vector coverage. The script uses the sql 'where' statement similar to this example:

SQL_STRING="ID=xxxx1 OR ID=xxxx2 OR ID=xxxx3"

ps.map output << EOF
vareas
where $SQL_STRING
<plot commands go here>
end
EOF

The SQL_STRING is read in from a file, and can contain more than 100 unique IDs.

This works great, BUT there appears to be a limit to the number of ID's (or characters) that are allowed in the string. The command fails when I have more than 64 IDs in the statement (just under 1000 characters). Later in the script, I use a similar 'where' statement in a v.extract command and have the same problem, so its not limited to ps.map.

My question: are there known length limits to the SQL select statement in GRASS? Or perhaps I some other problem?

Thanks for any help you can provide! Let me know if you need more info.

Steve

2

Stephen.King wrote:

I am a new listserver member with a grass64 problem.
I am hoping somebody can help me out:

I have a batch script that uses ps.map plot to select and
plot areas from a vector coverage. The script uses the
sql 'where' statement similar to this example:

SQL_STRING="ID=xxxx1 OR ID=xxxx2 OR ID=xxxx3"

ps.map output << EOF
vareas
where $SQL_STRING
<plot commands go here>
end
EOF

The SQL_STRING is read in from a file, and can contain more
than 100 unique IDs.

This works great, BUT there appears to be a limit to the
number of ID's (or characters) that are allowed in the
string. The command fails when I have more than 64 IDs
in the statement (just under 1000 characters). Later
in the script, I use a similar 'where' statement in a
v.extract command and have the same problem, so its not
limited to ps.map.

My question: are there known length limits to the SQL
select statement in GRASS? Or perhaps I some other
problem?

12 chars per ID * 100 IDs = 1200 chars

Both methods seem to be arbitrarily limited to 1023 characters
in the source code.

For ps.map as part of buf and G_getl2() and gobble_input() in
input.c, and for v.extract by lib/db/dbmi_client/select.c's
db_select_int() with buf and G_snprintf().

You could try replacing those 1024s with 4096s in the source
code and recompile..

maybe there are other places too..?

Maybe easier: Can you recreate the v.extract step with
db.execute? (with IDs read from a file)

or, are IDs the key column? (change with v.reclass)
If so v.extract list=1,2,3,4,...,n and ps.map/vareas
"cats 1,2,3,4,...,n" might help.

or, break it into two (repeat) steps, with 50 IDs per step.

Hamish