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Improve docs about numeric formatting patterns (to_char/to_number).

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The explanation about "0" versus "9" format characters was confusing
and arguably wrong; the discussion of sign handling wasn't very good
either.  Notably, while it's accurate to say that "FM" strips leading
zeroes in date/time values, what it really does with numeric values
is to strip *trailing* zeroes, and then only if you wrote "9" rather
than "0".  Per gripes from Erwin Brandstetter.

Discussion: https://postgr.es/m/CAGHENJ7jgRbTn6nf48xNZ=FHgL2WQ4X8mYsUAU57f-vq8PubEw@mail.gmail.com
Discussion: https://postgr.es/m/CAGHENJ45ymd=GOCu1vwV9u7GmCR80_5tW0fP9C_gJKbruGMHvQ@mail.gmail.com
This commit is contained in:
Tom Lane 2017-08-29 09:34:21 -04:00
parent dc4f356b44
commit ce5dcf54b9
1 changed files with 48 additions and 19 deletions
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67
doc/src/sgml/func.sgml
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@ -6351,11 +6351,11 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
<tbody>
<row>
<entry><literal>9</literal></entry>
<entry>value with the specified number of digits</entry>
<entry>digit position (can be dropped if insignificant)</entry>
</row>
<row>
<entry><literal>0</literal></entry>
<entry>value with leading zeros</entry>
<entry>digit position (will not be dropped, even if insignificant)</entry>
</row>
<row>
<entry><literal>.</literal> (period)</entry>
@ -6363,7 +6363,7 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
</row>
<row>
<entry><literal>,</literal> (comma)</entry>
<entry>group (thousand) separator</entry>
<entry>group (thousands) separator</entry>
</row>
<row>
<entry><literal>PR</literal></entry>
@ -6423,23 +6423,48 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
<itemizedlist>
<listitem>
<para>
A sign formatted using <literal>SG</literal>, <literal>PL</literal>, or
<literal>MI</literal> is not anchored to
the number; for example,
<literal>to_char(-12, 'MI9999')</literal> produces <literal>'-&nbsp;&nbsp;12'</literal>
but <literal>to_char(-12, 'S9999')</literal> produces <literal>'&nbsp;&nbsp;-12'</literal>.
The Oracle implementation does not allow the use of
<literal>MI</literal> before <literal>9</literal>, but rather
requires that <literal>9</literal> precede
<literal>MI</literal>.
<literal>0</> specifies a digit position that will always be printed,
even if it contains a leading/trailing zero. <literal>9</> also
specifies a digit position, but if it is a leading zero then it will
be replaced by a space, while if it is a trailing zero and fill mode
is specified then it will be deleted. (For <function>to_number()</>,
these two pattern characters are equivalent.)
</para>
</listitem>
<listitem>
<para>
<literal>9</literal> results in a value with the same number of
digits as there are <literal>9</literal>s. If a digit is
not available it outputs a space.
The pattern characters <literal>S</>, <literal>L</>, <literal>D</>,
and <literal>G</> represent the sign, currency symbol, decimal point,
and thousands separator characters defined by the current locale
(see <xref linkend="guc-lc-monetary">
and <xref linkend="guc-lc-numeric">). The pattern characters period
and comma represent those exact characters, with the meanings of
decimal point and thousands separator, regardless of locale.
</para>
</listitem>
<listitem>
<para>
If no explicit provision is made for a sign
in <function>to_char()</>'s pattern, one column will be reserved for
the sign, and it will be anchored to (appear just left of) the
number. If <literal>S</> appears just left of some <literal>9</>'s,
it will likewise be anchored to the number.
</para>
</listitem>
<listitem>
<para>
A sign formatted using <literal>SG</literal>, <literal>PL</literal>, or
<literal>MI</literal> is not anchored to
the number; for example,
<literal>to_char(-12, 'MI9999')</literal> produces <literal>'-&nbsp;&nbsp;12'</literal>
but <literal>to_char(-12, 'S9999')</literal> produces <literal>'&nbsp;&nbsp;-12'</literal>.
(The Oracle implementation does not allow the use of
<literal>MI</literal> before <literal>9</literal>, but rather
requires that <literal>9</literal> precede
<literal>MI</literal>.)
</para>
</listitem>
@ -6486,8 +6511,8 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
<para>
Certain modifiers can be applied to any template pattern to alter its
behavior. For example, <literal>FM9999</literal>
is the <literal>9999</literal> pattern with the
behavior. For example, <literal>FM99.99</literal>
is the <literal>99.99</literal> pattern with the
<literal>FM</literal> modifier.
<xref linkend="functions-formatting-numericmod-table"> shows the
modifier patterns for numeric formatting.
@ -6506,8 +6531,8 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
<tbody>
<row>
<entry><literal>FM</literal> prefix</entry>
<entry>fill mode (suppress leading zeroes and padding blanks)</entry>
<entry><literal>FM9999</literal></entry>
<entry>fill mode (suppress trailing zeroes and padding blanks)</entry>
<entry><literal>FM99.99</literal></entry>
</row>
<row>
<entry><literal>TH</literal> suffix</entry>
@ -6554,6 +6579,10 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
<entry><literal>to_char(-0.1, 'FM9.99')</literal></entry>
<entry><literal>'-.1'</literal></entry>
</row>
<row>
<entry><literal>to_char(-0.1, 'FM90.99')</literal></entry>
<entry><literal>'-0.1'</literal></entry>
</row>
<row>
<entry><literal>to_char(0.1, '0.9')</literal></entry>
<entry><literal>'&nbsp;0.1'</literal></entry>