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Add width_bucket(anyelement, anyarray).

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This provides a convenient method of classifying input values into buckets
that are not necessarily equal-width.  It works on any sortable data type.

The choice of function name is a bit debatable, perhaps, but showing that
there's a relationship to the SQL standard's width_bucket() function seems
more attractive than the other proposals.

Petr Jelinek, reviewed by Pavel Stehule
This commit is contained in:
Tom Lane
2014-09-09 15:34:10 -04:00
parent 220bb39dee
commit e80252d424
7 changed files with 458 additions and 12 deletions
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33
doc/src/sgml/func.sgml
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@ -901,25 +901,40 @@
<indexterm>
<primary>width_bucket</primary>
</indexterm>
<literal><function>width_bucket(<parameter>op</parameter> <type>numeric</type>, <parameter>b1</parameter> <type>numeric</type>, <parameter>b2</parameter> <type>numeric</type>, <parameter>count</parameter> <type>int</type>)</function></literal>
</entry>
<literal><function>width_bucket(<parameter>operand</parameter> <type>dp</type>, <parameter>b1</parameter> <type>dp</type>, <parameter>b2</parameter> <type>dp</type>, <parameter>count</parameter> <type>int</type>)</function></literal></entry>
<entry><type>int</type></entry>
<entry>return the bucket to which <parameter>operand</> would
be assigned in an equidepth histogram with <parameter>count</>
buckets, in the range <parameter>b1</> to <parameter>b2</></entry>
<entry>return the bucket number to which <parameter>operand</> would
be assigned in a histogram having <parameter>count</> equal-width
buckets spanning the range <parameter>b1</> to <parameter>b2</>;
returns <literal>0</> or <literal><parameter>count</>+1</literal> for
an input outside the range</entry>
<entry><literal>width_bucket(5.35, 0.024, 10.06, 5)</literal></entry>
<entry><literal>3</literal></entry>
</row>
<row>
<entry><literal><function>width_bucket(<parameter>op</parameter> <type>dp</type>, <parameter>b1</parameter> <type>dp</type>, <parameter>b2</parameter> <type>dp</type>, <parameter>count</parameter> <type>int</type>)</function></literal></entry>
<entry><literal><function>width_bucket(<parameter>operand</parameter> <type>numeric</type>, <parameter>b1</parameter> <type>numeric</type>, <parameter>b2</parameter> <type>numeric</type>, <parameter>count</parameter> <type>int</type>)</function></literal></entry>
<entry><type>int</type></entry>
<entry>return the bucket to which <parameter>operand</> would
be assigned in an equidepth histogram with <parameter>count</>
buckets, in the range <parameter>b1</> to <parameter>b2</></entry>
<entry>return the bucket number to which <parameter>operand</> would
be assigned in a histogram having <parameter>count</> equal-width
buckets spanning the range <parameter>b1</> to <parameter>b2</>;
returns <literal>0</> or <literal><parameter>count</>+1</literal> for
an input outside the range</entry>
<entry><literal>width_bucket(5.35, 0.024, 10.06, 5)</literal></entry>
<entry><literal>3</literal></entry>
</row>
<row>
<entry><literal><function>width_bucket(<parameter>operand</parameter> <type>anyelement</type>, <parameter>thresholds</parameter> <type>anyarray</type>)</function></literal></entry>
<entry><type>int</type></entry>
<entry>return the bucket number to which <parameter>operand</> would
be assigned given an array listing the lower bounds of the buckets;
returns <literal>0</> for an input less than the first lower bound;
the <parameter>thresholds</> array <emphasis>must be sorted</>,
smallest first, or unexpected results will be obtained</entry>
<entry><literal>width_bucket(now(), array['yesterday', 'today', 'tomorrow']::timestamptz[])</literal></entry>
<entry><literal>2</literal></entry>
</row>
</tbody>
</tgroup>
</table>