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    <h3>Procedural solution with PL/pgSQL</h3> <p>The problem is rather unwieldy for plain SQL with aggregate / windows functions. While looping is typically slower than set-based solutions with plain SQL, a procedural solution with plpgsql can make do with a <strong>single sequential scan</strong> over the table (implicit cursor of a <code>FOR</code> loop) and should be <strong><em>substantially faster in this particular case</em></strong>:</p> <p>Test table:</p> <pre><code>CREATE TEMP TABLE tbl (company text, profession text, year int); INSERT INTO tbl VALUES ('Google', 'Programmer', 2000) ,('Google', 'Sales', 2000) ,('Google', 'Sales', 2001) ,('Google', 'Sales', 2002) ,('Google', 'Sales', 2004) ,('Mozilla', 'Sales', 2002); </code></pre> <p>Function:</p> <pre><code>CREATE OR REPLACE FUNCTION f_periods() RETURNS TABLE (company text, profession text, years int[]) AS $func$ DECLARE r tbl; -- use table type as row variable r0 tbl; BEGIN FOR r IN SELECT * FROM tbl t ORDER BY t.company, t.profession, t.year LOOP IF ( r.company, r.profession, r.year) &lt;&gt; (r0.company, r0.profession, r0.year + 1) THEN -- not true for first row RETURN QUERY SELECT r0.company, r0.profession, years; -- output row years := ARRAY[r.year]; -- start new array ELSE years := years || r.year; -- add to array - year can be NULL, too END IF; r0 := r; -- remember last row END LOOP; RETURN QUERY -- output last iteration SELECT r0.company, r0.profession, years; END $func$ LANGUAGE plpgsql; </code></pre> <p>Call:</p> <pre><code>SELECT * FROM f_periods(); </code></pre> <p>Produces the requested result.</p>
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    1. POGROUP BY and aggregate sequential numeric values
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    1. USErwin Brandstetter
    1. USErwin Brandstetter
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    1. COSlightly edited examples to give you better idea. Notice Google,Sales returns 2 results, the first containing the years 2000, 2001, 2002 because they are in sequential order while 2004 is a separate entry because there is no 2003 to create a complete sequence.
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      1. USJoshua Burns
    2. CO@ErwinBrandstetter: Nice solution and I agree that your version is probably a lot faster as it requires only a single scan over the table.
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      1. USa_horse_with_no_name
    3. CO@a_horse_with_no_name: though I have to admit that your version is an impressive demonstration of what window functions *can* do.
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      1. USErwin Brandstetter
 

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