<para>

Time zones, and time-zone conventions, are influenced by

political decisions, not just earth geometry. Time zones around the

world became somewhat standardized during the1900's,

world became somewhat standardized during the1900s,

but continue to be prone to arbitrary changes, particularly with

respect to daylight-savings rules.

<productname>PostgreSQL</productname> uses the widely-used

<parameter>schema</> is the schema name that the object belongs in, or

<literal>NULL</> for object types that do not belong to schemas;

<parameter>name</> is the name of the object, quoted if necessary, only

present if it can be used (alongside schema name, if pertinent) asan unique

present if it can be used (alongside schema name, if pertinent) asa unique

identifier of the object, otherwise <literal>NULL</>;

<parameter>identity</> is the complete object identity, with the precise format

depending on object type, and each part within the format being

<entry><type>text</type></entry>

<entry>

Name of the object, if the combination of schema and name can be

used asan unique identifier for the object; otherwise <literal>NULL</>.

used asa unique identifier for the object; otherwise <literal>NULL</>.

No quoting is applied, and name is never schema-qualified.

</entry>

</row>

correctly. Advisory locks can be useful for locking strategies

that are an awkward fit for the MVCC model.

For example, a common use of advisory locks is to emulate pessimistic

locking strategies typical of socalled <quote>flat file</> data

locking strategies typical of so-called <quote>flat file</> data

management systems.

While a flag stored in a table could be used for the same purpose,

advisory locks are faster, avoid table bloat, and are automatically

(useful when multiple scripts were specified with <option>-f</>),

and <replaceable>time_epoch</>/<replaceable>time_us</> are a

UNIX epoch format timestamp and an offset

in microseconds (suitable for creatinga ISO 8601

in microseconds (suitable for creatingan ISO 8601

timestamp with fractional seconds) showing when

the transaction completed.

</para>

</synopsis>

<para>

Encrypt <parameter>data</> with a public PGP key <parameter>key</>.

Giving this function a secret key will producea error.

Giving this function a secret key will producean error.

</para>

<para>

The <parameter>options</> parameter can contain option settings,

Sometimes it is desirable to write Tcl functions that are not restricted

to safe Tcl. For example, one might want a Tcl function that sends

email. To handle these cases, there is a variant of <application>PL/Tcl</> called <literal>PL/TclU</>

(for untrusted Tcl). This isthe exact same language except that a full

(for untrusted Tcl). This isexactly the same language except that a full

Tcl interpreter is used. <emphasis>If <application>PL/TclU</> is used, it must be

installed as an untrusted procedural language</emphasis> so that only

database superusers can create functions in it. The writer of a <application>PL/TclU</>

statements in <literal>WITH</>, the order in which the specified updates

actually happen is unpredictable. All the statements are executed with

the same <firstterm>snapshot</> (see <xref linkend="mvcc">), so they

cannot <quote>see</>each others' effects on the target tables. This

cannot <quote>see</>one another's effects on the target tables. This

alleviates the effects of the unpredictability of the actual order of row

updates, and means that <literal>RETURNING</> data is the only way to

communicate changes between different <literal>WITH</> sub-statements and

</programlisting>

<para>

The following example command changes the language option to dutch,

The following example command changes the language option to<literal>dutch</>,

and removes the stopword option entirely.

</para>

COMMENT ON TABLE my_schema.my_table IS 'Employee Information';

COMMENT ON TABLESPACE my_tablespace IS 'Tablespace for indexes';

COMMENT ON TEXT SEARCH CONFIGURATION my_config IS 'Special word filtering';

COMMENT ON TEXT SEARCH DICTIONARY swedish IS 'Snowball stemmer forswedish language';

COMMENT ON TEXT SEARCH DICTIONARY swedish IS 'Snowball stemmer forSwedish language';

COMMENT ON TEXT SEARCH PARSER my_parser IS 'Splits text into words';

COMMENT ON TEXT SEARCH TEMPLATE snowball IS 'Snowball stemmer';

COMMENT ON TRIGGER my_trigger ON my_table IS 'Used for RI';

is also acquired by any <command>DELETE</> on a row, and also by an

<command>UPDATE</> that modifies the values on certain columns. Currently,

the set of columns considered for the <command>UPDATE</> case are those that

havean unique index on them that can be used in a foreign key (so partial

havea unique index on them that can be used in a foreign key (so partial

indexes and expressional indexes are not considered), but this may change

in the future.

Also, if an <command>UPDATE</command>, <command>DELETE</command>,