2010/6/25 Frank Bax <f...@sympatico.ca>:
> 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?
>
Try:
SELECT i, array_to_string(array_agg(foo), ' ') "Val"
FROM (SELECT * FROM (SELECT i, regexp_split_to_table(val, E'\\s+') AS
foo FROM t1) bar
LEFT OUTER JOIN t2 ON (bar.foo = t2.q) WHERE z IS DISTINCT FROM 'vowel') foobar
GROUP BY i;
i | Val
---+---------
1 | B C D
3 | G H I J
2 | B D F
(3 linhas)
Osvaldo
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