Sunday, April 22, 2012

a little bit about Oracle Quote Operator and Substitution Variables

keywords: oracle quote operator, substitution variables, set define, string, ampersand, global temporary table

I would like to share in this post one Oracle functionality that might save you some of your time. If you write PL/SQL code or if you are programming in some other language sql statements most probably you will have to write to database textual data that contain quotes or you will have to create SQL statement that inserts varchar into database. In this case or other similar cases you will have to struggle with lot of quote signs. To circumvent all that trouble try to use Oracle quote operator.
Here is how it works:
   l_str varchar2(30) := q'[I’ll quote!]';
or just simple select
select q'[i’ll quote!]' from dual;
Last time I used this Oracle functionality introduced in Oracle 10g I had to store in database many predefined CQL filters and http requests GetLegendGraphic (the intention was to store configuration for the Web GIS application in database; Geoserver was GIS engine used on server side). Besides CQL and Legend elements I had to store some other configuration elements in database but for this post I would like to present you one more thing that can be helpful working with strings... especially if you are storing url in database table.
Here is example of url I had to store in database.
It is standard GET request that contains ampersand signs. To demonstrate what is so special with GET request I have prepared for you several SQL statements.... so.... open your SQL plus and try to run it.... First create table for testing, than try to run script 1 and than script 2... after testing remove table....
--to create table:
create global temporary table my_test_table (
 test_string  varchar2(1000)
) on commit preserve rows;
--to remove table:
truncate table my_test_table;
drop table my_test_table;
--script 1
set define off;
insert into  my_test_table
values (q'[../geoserver/wms?REQUEST=GetLegendGraphic&VERSION=1.0.0&FORMAT=image/png&WIDTH=20&HEIGHT=20&LAYER=PP:COUNTY]');
Try to execute the same statement but now with option set define on.
--script 2
set define on;
insert into  my_test_table
values (q'[../geoserver/wms?REQUEST=GetLegendGraphic&VERSION=1.0.0&FORMAT=image/png&WIDTH=20&HEIGHT=20&LAYER=PP:COUNTY]');
You will notice difference immediately :-)
… and If you didn’t know about oracle substitution variables maybe now you can find some interesting application for that functionality …..

On this link you can read more about it.

… enjoy …

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