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Add bit_count SQL function

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This function for bit and bytea counts the set bits in the bit or byte
string.  Internally, we use the existing popcount functionality.

For the name, after some discussion, we settled on bit_count, which
also exists with this meaning in MySQL, Java, and Python.

Author: David Fetter <david@fetter.org>
Discussion: https://www.postgresql.org/message-id/flat/20201230105535.GJ13234@fetter.org
This commit is contained in:
Peter Eisentraut
2021-03-23 08:45:51 +01:00
parent 5aed6a1fc2
commit a6715af1e7
9 changed files with 97 additions and 1 deletions
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40
doc/src/sgml/func.sgml
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@ -4010,6 +4010,28 @@ SELECT format('Testing %3$s, %2$s, %s', 'one', 'two', 'three');
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_count</primary>
</indexterm>
<indexterm>
<primary>popcount</primary>
<see>bit_count</see>
</indexterm>
<function>bit_count</function> ( <parameter>bytes</parameter> <type>bytea</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the number of bits set in the binary string (also known as
<quote>popcount</quote>).
</para>
<para>
<literal>bit_count('\x1234567890'::bytea)</literal>
<returnvalue>31</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
@ -4714,6 +4736,24 @@ SELECT format('Testing %3$s, %2$s, %s', 'one', 'two', 'three');
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_count</primary>
</indexterm>
<function>bit_count</function> ( <type>bit</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the number of bits set in the bit string (also known as
<quote>popcount</quote>).
</para>
<para>
<literal>bit_count(B'10111')</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>