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Re^3: Interpolating subroutine call in SQL INSERT INTO SELECT statement

by chacham (Prior)
on Aug 27, 2015 at 16:37 UTC ( #1140232=note: print w/replies, xml ) Need Help??


in reply to Re^2: Interpolating subroutine call in SQL INSERT INTO SELECT statement
in thread Interpolating subroutine call in SQL INSERT INTO SELECT statement

if there was a clever way to intersperse/embed my function within the INSERT INTO/SELECT construct

That depends on what you want done and what language the function would be in. What exactly are you trying to do?

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Re^4: Interpolating subroutine call in SQL INSERT INTO SELECT statement
by shadowsong (Pilgrim) on Aug 28, 2015 at 09:16 UTC

    chacham,

    What I was trying ascertain was whether I could invoke my perl function (at the end of this comment) within the midst of the SQL INSERT INTO/SELECT FROM statement. Now, the following responses from other monks confirmed my suspicions...

    You might be able to do simple interpolation using nothing but SQL inline with a few subqueries and some trivial math.

    If you truley need a perl function to do the job, you'll have to do a select in one call. And then prep an insert data set for a second call.
    KurtSchwind


    The very-short (but definitive) answer is ... “no.”

    And here’s why: “any ... SQL server has no idea who-or-what its client is ... nor does it care.” The server knows nothing about you ... therefore, nothing about your programming language (or even that you are using one ...) ... therefore, nothing about your “functions.” It has no ability,whatsoever, to “call them.”

    If you desire to “do something fancy,” then you must provide all of the code to do it. You must issue a SELECT statement, and, for each row returned, create and issue appropriate-to-you INSERTs, probably within a transaction.
    sundialsvc4

    I also considered this from 1nickt...

    Even a broken clock is right once every 86400 seconds. But did you read and follow the other advice given in response to your question, where a number of experienced programmers explained how you can create a function in your SQL?

    Vicar poj was also very kind to provide examples of how to create SQL functions in perl and use them. So I believe I'm now straight on what I can and can't do... Here's the function I coded in perl to modify COLUMN3 before inserting it back into TABLE1.

    sub convert { ### This subroutine accepts a single parameter (a scalar which it +treats as a string) ### and sequentially substitutes out "invalid" characters with the +ir "valid" counterparts ### based on a fixed list of characters to replace. my $input_stream = shift; return undef unless $input_stream; my %char_swap_hash = ( 1 => {OLD => '&[^(amp;)|(lt;)|(gt;)]', NEW => '&amp;'}, # don' +t match legit '&' codes 2 => {OLD => '<', NEW => '&lt;'}, 3 => {OLD => '>', NEW => '&gt;'} ); $input_stream =~ s/$char_swap_hash{$_}{OLD}/$char_swap_hash{$_}{NE +W}/g for keys %char_swap_hash; return $input_stream; }

      The match for 1 is incorrect, you can't use a character class like that. Try this test

      #!perl use strict; use YAPE::Regex::Explain; my $str = '&gt; milk &amp; honey &lt; < bill&ben >'; sub convert { my $input_stream = shift; return undef unless $input_stream; my %char_swap_hash = ( 1 => {OLD => '&[^(amp;)|(lt;)|(gt;)]', NEW => '&amp;'}, # don't mat +ch legit '&' codes 2 => {OLD => '<', NEW => '&lt;'}, 3 => {OLD => '>', NEW => '&gt;'} ); $input_stream =~ s/$char_swap_hash{$_}{OLD}/$char_swap_hash{$_}{NEW} +/g for keys %char_swap_hash; return $input_stream; } print YAPE::Regex::Explain->new('&[^(amp;)|(lt;)|(gt;)]')->explain; print convert($str),"\n";

      Alternative

      my %htm = ( '&' => '&amp;', '>' => '&gt;', '<' => '&lt;', ); my $REx = qr'(&(?!(?:amp|lt|gt);)|[><])'; $str =~ s/$REx/$htm{$1}/g; print $str."\n\n"; print YAPE::Regex::Explain->new($REx)->explain;
      poj

        poj - you're right...

        While testing it I realized I was getting back dodgy results, it turns out what I needed to do was use negative lookahead

        I ended up changing the value of key 1 in %char_swap_hash to this:

        1 => {OLD => '&(?!(amp;)|(lt;)|(gt;))', NEW => '&amp;'}, # don't match + legit '&' codes

        I then saw your solution which not only confirmed that attempting to use a character class to evaluate lookaheads was bonkers but introduced me YAPE::Regex::Explain - which at the moment isn't being found by cpanm (so I am unable to easily install and use it; which is more than a little irritating)

        However, many thanks poj - I appreciate all your help.

      SQL forums are often filled with question of how to do fancy things, and the answer is usually not with a custom function. Between joins, where clauses, with clauses, and recursive queries, you can do quite a bit. It's important to state what you are to do as opposed to deciding a solution and asking how to implement it. For all you know, the best answer might even be perl based!

      You can choose to share or not to share. People here are often willing to help if you let them.

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