- 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
- array_nulls (boolean)
This controls whether the array input parser recognizes
unquoted NULL as specifying a null array element.
By default, this is on, allowing array values containing
null values to be entered. However, PostgreSQL versions
before 8.2 did not support null values in arrays, and therefore would
treat NULL as specifying a normal array element with
the string value "NULL". For backwards compatibility with
applications that require the old behavior, this variable can be
Note that it is possible to create array values containing null values
even when this variable is off.
- backslash_quote (enum)
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.
Note that in a standard-conforming string literal, \ just
means \ anyway. This parameter affects the handling of
non-standard-conforming literals, including
escape string syntax (E'...').
- 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 off 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) and standard_conforming_strings is off.
The default is on.
Applications that wish to use backslash as escape should be
modified to use escape string syntax (E'...'),
because the default behavior of ordinary strings will change
in a future release for SQL compatibility. This variable can
be enabled to help detect applications that will break.
- regex_flavor (enum)
The regular expression "flavor" can be set to
advanced, extended, or basic.
The default is advanced. The extended
setting might be useful for exact backwards compatibility with
pre-7.4 releases of PostgreSQL. See
Section 220.127.116.11 for details.
- sql_inheritance (boolean)
This setting controls whether undecorated table references are
considered to include inheritance child tables. The default is
on, which means child tables are included (thus,
a * suffix is assumed by default). If turned
off, child tables are not included (thus, an
ONLY prefix is assumed). The SQL standard
requires child tables to be included, so the off setting
is not spec-compliant, but it is provided for compatibility with
PostgreSQL releases prior to 7.1.
See Section 5.8 for more information.
Turning sql_inheritance off is deprecated, because that
behavior has been found to be error-prone as well as contrary to SQL
standard. Discussions of inheritance behavior elsewhere in this
manual generally assume that it is on.
- standard_conforming_strings (boolean)
This controls whether ordinary string literals
('...') treat backslashes literally, as specified in
the SQL standard.
The default is currently off, causing
PostgreSQL to have its historical
behavior of treating backslashes as escape characters.
The default will change to on in a future release
to improve compatibility with the standard.
Applications can check this
parameter to determine how string literals will be processed.
The presence of this parameter can also be taken as an indication
that the escape string syntax (E'...') is supported.
Escape string syntax should be used if an application desires
backslashes to be treated as escape characters.
- synchronize_seqscans (boolean)
This allows sequential scans of large tables to synchronize with each
other, so that concurrent scans read the same block at about the
same time and hence share the I/O workload. When this is enabled,
a scan might start in the middle of the table and then "wrap
around" the end to cover all rows, so as to synchronize with the
activity of scans already in progress. This can result in
unpredictable changes in the row ordering returned by queries that
have no ORDER BY clause. Setting this parameter to
off ensures the pre-8.3 behavior in which a sequential
scan always starts from the beginning of the table. The default