Message-ID: <BLU0-SMTP789E97372809C06816956AACC70@phx.gbl>
Date: Fri, 25 Jun 2010 18:23:48 -0400
From: Frank Bax <fbax@sympatico.ca>
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To: pgsql-sql@postgresql.org
Subject: How do I remove selected words from text field?
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I'm not quite sure how to ask for the query I want, so let's start with 
data:

create table t1 (i int, val varchar);
insert into t1 values(1,'A B C D');
insert into t1 values(2,'B D E F');
insert into t1 values(3,'G H I J');
create table t2 (q varchar, z varchar);
insert into t2 values('A','vowel');
insert into t2 values('B','consonant');
insert into t2 values('E','vowel');
insert into t2 values('K','consonant');

t1.val will contain "words" separated by blanks.  It might be better if 
each "word" were a separate row in another table; but that's not how the 
legacy database was built.  I understand this can be simulated by:

select i,a[s] from (select i, generate_subscripts(string_to_array(val,' 
'),1) as s, string_to_array(val,' ') as a from t1) foo;

In my "real life" situation, the "words" are not single letters.

I'd like to write a function that removes selected "words" from t1.val 
based on select on t2.
In the above example; let's exclude all vowels, so I end up with:
1 'B C D'
2 'B D F'
3 'G H I J'

For some "words" in val; there may not be a row when joining to t2.q; 
these words must be included in final result.  In the above example; 
there is no row in t2 where q="I"; so it is included in result.

How do I write such a function?  Can it be done with SQL only?