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2013-05-25T18:54:30.157
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I don't have an 8.4 handy but in more recent versions, the <code>array_to_string</code> is ignoring your NULLs so the problem isn't <code>array_agg</code>, it is <code>array_to_string</code>. For example: <pre><code>=> select distinct state from orders; state --------- success failure </code></pre> That blank line is in fact a NULL. Then we can see what <code>array_agg</code> and <code>array_to_string</code> do with this stuff: <pre><code>=> select array_agg(distinct state) from orders; array_agg ------------------------ {failure,success,NULL} => select array_to_string(array_agg(distinct state), ',') from orders; array_to_string ----------------- failure,success </code></pre> And the NULL disappears in the <code>array_to_string</code> call. The <a href="http://www.postgresql.org/docs/8.4/interactive/functions-array.html#ARRAY-FUNCTIONS-TABLE" rel="nofollow">documentation</a> doesn't specify any particular handling of NULLs but ignoring them seems as reasonable as anything else. In version 9.x you can get around this using, as usual, <a href="http://www.postgresql.org/docs/8.4/static/functions-conditional.html#AEN15275" rel="nofollow">COALESCE</a>: <pre><code>=> select array_to_string(array_agg(distinct coalesce(state, '')), ',') from orders; array_to_string ------------------ ,failure,success </code></pre> So perhaps this will work for you: <pre><code>array_to_string(array_agg(DISTINCT coalesce(class_low, '')), ',') </code></pre> Of course that will fold NULLs and empty strings into one value, that may or may not be an issue.
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