add_missing_from
(boolean
)
When on, tables that are referenced by a query will be
automatically added to the FROM
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 off
. This variable can be
enabled for compatibility with releases of
PostgreSQL prior to 8.1, where this behavior was
allowed by default.
Note that even when this variable is enabled, a warning
message will be emitted for each implicit FROM
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 FROM
clause (or its USING
clause in the case of
DELETE
).
regex_flavor
(string
)
The regular expression “flavor” can be set to
advanced
, extended
, or basic
.
The default is advanced
. The extended
setting may be useful for exact backwards compatibility with
pre-7.4 releases of PostgreSQL. See
Section 9.7.3.1, “Regular Expression Details” for details.
sql_inheritance
(boolean
)
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 off
, but in
the long run you are encouraged to change your applications to
use the ONLY
key word to exclude subtables.
See Section 5.8, “Inheritance” for more information about
inheritance.
backslash_quote
(string
)
This controls whether a quote mark can be represented by
\'
in a string literal. The preferred, SQL-standard way
to represent a quote mark is by doubling it (''
) but
PostgreSQL has historically also accepted
\'
. However, use of \'
creates security risks
because in some client character set encodings, there are multibyte
characters in which the last byte is numerically equivalent to ASCII
\
. 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 backslash_quote
are
on
(allow \'
always),
off
(reject always), and
safe_encoding
(allow only if client encoding does not
allow ASCII \
within a multibyte character).
safe_encoding
is the default setting.
default_with_oids
(boolean
)
This controls whether CREATE TABLE
and
CREATE TABLE AS
include an OID column in
newly-created tables, if neither WITH OIDS
nor WITHOUT OIDS
is specified. It also
determines whether OIDs will be included in tables created by
SELECT INTO
. In PostgreSQL
8.1 default_with_oids
is disabled by default; in
prior versions of PostgreSQL, it
was on by default.
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 WITH OIDS
when creating the
table. This variable can be enabled for compatibility with old
applications that do not follow this behavior.
escape_string_warning
(boolean
)
When on, a warning is issued if a backslash (\
)
appears in an ordinary string literal ('...'
syntax). The default is off
.
Escape string syntax (E'...'
) should be used for
escapes, because in future versions of
PostgreSQL ordinary strings will have
the standard-conforming behavior of treating backslashes
literally.
transform_null_equals
(boolean
)
When on, expressions of the form
(or expr
=
NULLNULL =
) are treated as
expr
, that is, they
return true if expr
IS NULLexpr
evaluates to the null value,
and false otherwise. The correct SQL-spec-compliant behavior of
is to always
return null (unknown). Therefore this option defaults to
expr
= NULLoff
.
However, filtered forms in Microsoft
Access generate queries that appear to use
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 expr
= NULL
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.
expr
= NULL
Note that this option only affects the exact form = NULL
,
not other comparison operators or other expressions
that are computationally equivalent to some expression
involving the equals operator (such as IN
).
Thus, this option is not a general fix for bad programming.
Refer to Section 9.2, “Comparison Operators” for related information.