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>PostgreSQL 8.1.9 Documentation</TH
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>Chapter 17. Server Configuration</TD
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><DIV
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><H1
CLASS="SECT1"
><A
NAME="RUNTIME-CONFIG-COMPATIBLE"
>17.12. Version and Platform Compatibility</A
></H1
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="RUNTIME-CONFIG-COMPATIBLE-VERSION"
>17.12.1. Previous PostgreSQL Versions</A
></H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="GUC-ADD-MISSING-FROM"
></A
><TT
CLASS="VARNAME"
>add_missing_from</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
> When on, tables that are referenced by a query will be
automatically added to the <TT
CLASS="LITERAL"
>FROM</TT
> clause if not
already present. This behavior does not comply with the SQL
standard and many people dislike it because it can mask mistakes
(such as referencing a table where you should have referenced
its alias). The default is <TT
CLASS="LITERAL"
>off</TT
>. This variable can be
enabled for compatibility with releases of
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> prior to 8.1, where this behavior was
allowed by default.
</P
><P
> Note that even when this variable is enabled, a warning
message will be emitted for each implicit <TT
CLASS="LITERAL"
>FROM</TT
>
entry referenced by a query. Users are encouraged to update
their applications to not rely on this behavior, by adding all
tables referenced by a query to the query's <TT
CLASS="LITERAL"
>FROM</TT
>
clause (or its <TT
CLASS="LITERAL"
>USING</TT
> clause in the case of
<TT
CLASS="COMMAND"
>DELETE</TT
>).
</P
></DD
><DT
><A
NAME="GUC-REGEX-FLAVOR"
></A
><TT
CLASS="VARNAME"
>regex_flavor</TT
> (<TT
CLASS="TYPE"
>string</TT
>)</DT
><DD
><P
> The regular expression <SPAN
CLASS="QUOTE"
>"flavor"</SPAN
> can be set to
<TT
CLASS="LITERAL"
>advanced</TT
>, <TT
CLASS="LITERAL"
>extended</TT
>, or <TT
CLASS="LITERAL"
>basic</TT
>.
The default is <TT
CLASS="LITERAL"
>advanced</TT
>. The <TT
CLASS="LITERAL"
>extended</TT
>
setting may be useful for exact backwards compatibility with
pre-7.4 releases of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>. See
<A
HREF="functions-matching.html#POSIX-SYNTAX-DETAILS"
>Section 9.7.3.1</A
> for details.
</P
></DD
><DT
><A
NAME="GUC-SQL-INHERITANCE"
></A
><TT
CLASS="VARNAME"
>sql_inheritance</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
> This controls the inheritance semantics, in particular whether
subtables are included by various commands by default. They were
not included in versions prior to 7.1. If you need the old
behavior you can set this variable to <TT
CLASS="LITERAL"
>off</TT
>, but in
the long run you are encouraged to change your applications to
use the <TT
CLASS="LITERAL"
>ONLY</TT
> key word to exclude subtables.
See <A
HREF="ddl-inherit.html"
>Section 5.8</A
> for more information about
inheritance.
</P
></DD
><DT
><A
NAME="GUC-BACKSLASH-QUOTE"
></A
><TT
CLASS="VARNAME"
>backslash_quote</TT
> (<TT
CLASS="TYPE"
>string</TT
>)</DT
><DD
><P
> This controls whether a quote mark can be represented by
<TT
CLASS="LITERAL"
>\'</TT
> in a string literal. The preferred, SQL-standard way
to represent a quote mark is by doubling it (<TT
CLASS="LITERAL"
>''</TT
>) but
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> has historically also accepted
<TT
CLASS="LITERAL"
>\'</TT
>. However, use of <TT
CLASS="LITERAL"
>\'</TT
> creates security risks
because in some client character set encodings, there are multibyte
characters in which the last byte is numerically equivalent to ASCII
<TT
CLASS="LITERAL"
>\</TT
>. If client-side code does escaping incorrectly then a
SQL-injection attack is possible. This risk can be prevented by
making the server reject queries in which a quote mark appears to be
escaped by a backslash.
The allowed values of <TT
CLASS="VARNAME"
>backslash_quote</TT
> are
<TT
CLASS="LITERAL"
>on</TT
> (allow <TT
CLASS="LITERAL"
>\'</TT
> always),
<TT
CLASS="LITERAL"
>off</TT
> (reject always), and
<TT
CLASS="LITERAL"
>safe_encoding</TT
> (allow only if client encoding does not
allow ASCII <TT
CLASS="LITERAL"
>\</TT
> within a multibyte character).
<TT
CLASS="LITERAL"
>safe_encoding</TT
> is the default setting.
</P
></DD
><DT
><A
NAME="GUC-DEFAULT-WITH-OIDS"
></A
><TT
CLASS="VARNAME"
>default_with_oids</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
> This controls whether <TT
CLASS="COMMAND"
>CREATE TABLE</TT
> and
<TT
CLASS="COMMAND"
>CREATE TABLE AS</TT
> include an OID column in
newly-created tables, if neither <TT
CLASS="LITERAL"
>WITH OIDS</TT
>
nor <TT
CLASS="LITERAL"
>WITHOUT OIDS</TT
> is specified. It also
determines whether OIDs will be included in tables created by
<TT
CLASS="COMMAND"
>SELECT INTO</TT
>. In <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
8.1 <TT
CLASS="VARNAME"
>default_with_oids</TT
> is disabled by default; in
prior versions of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, it
was on by default.
</P
><P
> The use of OIDs in user tables is considered deprecated, so
most installations should leave this variable disabled.
Applications that require OIDs for a particular table should
specify <TT
CLASS="LITERAL"
>WITH OIDS</TT
> when creating the
table. This variable can be enabled for compatibility with old
applications that do not follow this behavior.
</P
></DD
><DT
><A
NAME="GUC-ESCAPE-STRING-WARNING"
></A
><TT
CLASS="VARNAME"
>escape_string_warning</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
> When on, a warning is issued if a backslash (<TT
CLASS="LITERAL"
>\</TT
>)
appears in an ordinary string literal (<TT
CLASS="LITERAL"
>'...'</TT
>
syntax). The default is <TT
CLASS="LITERAL"
>off</TT
>.
</P
><P
> Escape string syntax (<TT
CLASS="LITERAL"
>E'...'</TT
>) should be used for
escapes, because in future versions of
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> ordinary strings will have
the standard-conforming behavior of treating backslashes
literally.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="RUNTIME-CONFIG-COMPATIBLE-CLIENTS"
>17.12.2. Platform and Client Compatibility</A
></H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="GUC-TRANSFORM-NULL-EQUALS"
></A
><TT
CLASS="VARNAME"
>transform_null_equals</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
> When on, expressions of the form <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>expr</I
></TT
> =
NULL</TT
> (or <TT
CLASS="LITERAL"
>NULL =
<TT
CLASS="REPLACEABLE"
><I
>expr</I
></TT
></TT
>) are treated as
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>expr</I
></TT
> IS NULL</TT
>, that is, they
return true if <TT
CLASS="REPLACEABLE"
><I
>expr</I
></TT
> evaluates to the null value,
and false otherwise. The correct SQL-spec-compliant behavior of
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>expr</I
></TT
> = NULL</TT
> is to always
return null (unknown). Therefore this option defaults to
<TT
CLASS="LITERAL"
>off</TT
>.
</P
><P
> However, filtered forms in <SPAN
CLASS="PRODUCTNAME"
>Microsoft
Access</SPAN
> generate queries that appear to use
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>expr</I
></TT
> = NULL</TT
> to test for
null values, so if you use that interface to access the database you
might want to turn this option on. Since expressions of the
form <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>expr</I
></TT
> = NULL</TT
> always
return the null value (using the correct interpretation) they are not
very useful and do not appear often in normal applications, so
this option does little harm in practice. But new users are
frequently confused about the semantics of expressions
involving null values, so this option is not on by default.
</P
><P
> Note that this option only affects the exact form <TT
CLASS="LITERAL"
>= NULL</TT
>,
not other comparison operators or other expressions
that are computationally equivalent to some expression
involving the equals operator (such as <TT
CLASS="LITERAL"
>IN</TT
>).
Thus, this option is not a general fix for bad programming.
</P
><P
> Refer to <A
HREF="functions-comparison.html"
>Section 9.2</A
> for related information.
</P
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