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Add three-parameter forms of array_to_string and string_to_array, to allow

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better handling of NULL elements within the arrays.  The third parameter
is a string that should be used to represent a NULL element, or should
be translated into a NULL element, respectively.  If the third parameter
is NULL it behaves the same as the two-parameter form.

There are two incompatible changes in the behavior of the two-parameter form
of string_to_array.  First, it will return an empty (zero-element) array
rather than NULL when the input string is of zero length.  Second, if the
field separator is NULL, the function splits the string into individual
characters, rather than returning NULL as before.  These two changes make
this form fully compatible with the behavior of the new three-parameter form.

Pavel Stehule, reviewed by Brendan Jurd
This commit is contained in:
Tom Lane
2010-08-10 21:51:00 +00:00
parent 5148a04636
commit 33f43725fb
9 changed files with 390 additions and 95 deletions
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48
doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.525 2010/08/08 19:15:27 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.526 2010/08/10 21:51:00 tgl Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -9736,13 +9736,14 @@ SELECT NULLIF(value, '(none)') ...
<row>
<entry>
<literal>
<function>array_to_string</function>(<type>anyarray</type>, <type>text</type>)
<function>array_to_string</function>(<type>anyarray</type>, <type>text</type> <optional>, <type>text</type></optional>)
</literal>
</entry>
<entry><type>text</type></entry>
<entry>concatenates array elements using supplied delimiter</entry>
<entry><literal>array_to_string(ARRAY[1, 2, 3], '~^~')</literal></entry>
<entry><literal>1~^~2~^~3</literal></entry>
<entry>concatenates array elements using supplied delimiter and
optional null string</entry>
<entry><literal>array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*')</literal></entry>
<entry><literal>1,2,3,*,5</literal></entry>
</row>
<row>
<entry>
@ -9758,13 +9759,14 @@ SELECT NULLIF(value, '(none)') ...
<row>
<entry>
<literal>
<function>string_to_array</function>(<type>text</type>, <type>text</type>)
<function>string_to_array</function>(<type>text</type>, <type>text</type> <optional>, <type>text</type></optional>)
</literal>
</entry>
<entry><type>text[]</type></entry>
<entry>splits string into array elements using supplied delimiter</entry>
<entry><literal>string_to_array('xx~^~yy~^~zz', '~^~')</literal></entry>
<entry><literal>{xx,yy,zz}</literal></entry>
<entry>splits string into array elements using supplied delimiter and
optional null string</entry>
<entry><literal>string_to_array('xx~^~yy~^~zz', '~^~', 'yy')</literal></entry>
<entry><literal>{xx,NULL,zz}</literal></entry>
</row>
<row>
<entry>
@ -9781,6 +9783,34 @@ SELECT NULLIF(value, '(none)') ...
</tgroup>
</table>
<para>
In <function>string_to_array</function>, if the delimiter parameter is
NULL, each character in the input string will become a separate element in
the resulting array. If the delimiter is an empty string, then the entire
input string is returned as a one-element array. Otherwise the input
string is split at each occurrence of the delimiter string.
</para>
<para>
In <function>string_to_array</function>, if the null-string parameter
is omitted or NULL, none of the substrings of the input will be replaced
by NULL.
In <function>array_to_string</function>, if the null-string parameter
is omitted or NULL, any null elements in the array are simply skipped
and not represented in the output string.
</para>
<note>
<para>
There are two differences in the behavior of <function>string_to_array</>
from pre-9.1 versions of <productname>PostgreSQL</>.
First, it will return an empty (zero-element) array rather than NULL when
the input string is of zero length. Second, if the delimiter string is
NULL, the function splits the input into individual characters, rather
than returning NULL as before.
</para>
</note>
<para>
See also <xref linkend="functions-aggregate"> about the aggregate
function <function>array_agg</function> for use with arrays.