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First version of files from Oliver Elphick.

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This commit is contained in:
Thomas G. Lockhart 1998-07-14 03:47:34 +00:00
parent 0acc52ae91
commit 3733bd4627
5 changed files with 2405 additions and 1 deletions
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6
doc/src/sgml/ref/commands.sgml
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@ -16,6 +16,10 @@
&createFunction;
&createIndex;
&createLanguage;
&createOperator;
&createRule;
&createSequence;
&createTable;
&dropFunction;
&select;
@ -36,4 +40,4 @@ sgml-exposed-tags:nil
sgml-local-catalogs:"/usr/lib/sgml/catalog"
sgml-local-ecat-files:nil
End:
-->
-->

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doc/src/sgml/ref/create_operator.sgml Normal file
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<REFENTRY ID="SQL-CREATEOPERATOR-1">
<REFMETA>
<REFENTRYTITLE>
CREATE OPERATOR
</REFENTRYTITLE>
<REFMISCINFO>SQL - Language Statements</REFMISCINFO>
</REFMETA>
<REFNAMEDIV>
<REFNAME>
CREATE OPERATOR
</REFNAME>
<REFPURPOSE>
Defines a new user operator.
</REFPURPOSE>
<REFSYNOPSISDIV>
<REFSYNOPSISDIVINFO>
<DATE>1998-04-15</DATE>
</REFSYNOPSISDIVINFO>
<SYNOPSIS>
CREATE OPERATOR <replaceable>name</replaceable>
([ LEFTARG = <replaceable class="parameter">type1</replaceable> ]
[, RIGHTARG = <replaceable class="parameter">type2</replaceable> ]
, PROCEDURE = <replaceable class="parameter">func_name</replaceable>
[, COMMUTATOR = <replaceable class="parameter">com_op</replaceable> ]
[, NEGATOR = <replaceable class="parameter">neg_op</replaceable> ]
[, RESTRICT = <replaceable class="parameter">res_proc</replaceable> ]
[, HASHES ]
[, JOIN = <replaceable class="parameter">join_proc</replaceable> ]
[, SORT = <replaceable class="parameter">sort_op</replaceable> [, ...] ]
)
</SYNOPSIS>
<REFSECT2 ID="R2-SQL-CREATEOPERATOR-1">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Inputs
</TITLE>
<PARA>
</PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
</TERM>
<LISTITEM>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">name</replaceable>
</TERM>
<LISTITEM>
<PARA>
The name of an existing aggregate function.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">type1</replaceable>
</TERM>
<LISTITEM>
<PARA>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">type2</replaceable>
</TERM>
<LISTITEM>
<PARA>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">func_name</replaceable>
</TERM>
<LISTITEM>
<PARA>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">com_op</replaceable>
</TERM>
<LISTITEM>
<PARA>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">neg_op</replaceable>
</TERM>
<LISTITEM>
<PARA>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">res_proc</replaceable>
</TERM>
<LISTITEM>
<PARA>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">join_proc</replaceable>
</TERM>
<LISTITEM>
<PARA>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">sort_op</replaceable>
</TERM>
<LISTITEM>
<PARA>
</PARA>
</LISTITEM>
</VARLISTENTRY>
</variablelist>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</REFSECT2>
<REFSECT2 ID="R2-SQL-CREATEOPERATOR-2">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Outputs
</TITLE>
<PARA>
</PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
</TERM>
<LISTITEM>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<ReturnValue>CREATE</ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Message returned if the operator is successfully created.
</PARA>
</LISTITEM>
</VARLISTENTRY>
</variablelist>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</REFSECT2>
</REFSYNOPSISDIV>
<REFSECT1 ID="R1-SQL-CREATEOPERATOR-1">
<REFSECT1INFO>
<DATE>1998-04-15</DATE>
</REFSECT1INFO>
<TITLE>
Description
</TITLE>
<PARA>
This command defines a new user operator, operator_name.
The user who defines an operator becomes its owner.
</para>
<para>
The operator_name is a sequence of up to sixteen punctua
tion characters. The following characters are valid for
single-character operator names:<literallayout>
~ ! @ # % ^ & ` ? </literallayout>
</para>
<para>
If the operator name is more than one character long, it
may consist of any combination of the above characters or
the following additional characters:<literallayout>
| $ : + - * / &lt; &gt; =</literallayout>
</para>
<para>
The operator "!=" is mapped to "&lt;&gt;" on input, and they are
therefore equivalent.
</para>
<para>
At least one of leftarg and rightarg must be defined. For
binary operators, both should be defined. For right unary
operators, only arg1 should be defined, while for left
unary operators only arg2 should be defined.
</para>
<para>
The name of the operator, operator_name, can be composed
of symbols only. Also, the func_name procedure must have
been previously defined using create function(l) and must
have one or two arguments.
</para>
<para>
The commutator operator is present so that Postgres can
reverse the order of the operands if it wishes. For exam
ple, the operator area-less-than, >>>, would have a commu
tator operator, area-greater-than, <<<. Suppose that an
operator, area-equal, ===, exists, as well as an area not
equal, !==. Hence, the query optimizer could freely con
vert:
<programlisting>
"0,0,1,1"::box >>> MYBOXES.description
</programlisting>
to
<programlisting>
MYBOXES.description <<< "0,0,1,1"::box</programlisting>
</para>
<para>
This allows the execution code to always use the latter
representation and simplifies the query optimizer some
what.
</para>
<para>
The negator operator allows the query optimizer to convert
<programlisting>
NOT MYBOXES.description === "0,0,1,1"::box
</programlisting>
to
<programlisting>
MYBOXES.description !== "0,0,1,1"::box
</programlisting>
</para>
<para>
If a commutator operator name is supplied, Postgres
searches for it in the catalog. If it is found and it
does not yet have a commutator itself, then the commutator's
entry is updated to have the current (new) operator
as its commutator. This applies to the negator, as well.
</para>
<para>
This is to allow the definition of two operators that are
the commutators or the negators of each other. The first
operator should be defined without a commutator or negator
(as appropriate). When the second operator is defined,
name the first as the commutator or negator. The first
will be updated as a side effect.
</para>
<para>
The next two specifications are present to support the
query optimizer in performing joins. Postgres can always
evaluate a join (i.e., processing a clause with two tuple
variables separated by an operator that returns a boolean)
by iterative substitution [WONG76]. In addition, Postgres
is planning on implementing a hash-join algorithm along
the lines of [SHAP86]; however, it must know whether this
strategy is applicable. For example, a hash-join
algorithm is usable for a clause of the form:
<programlisting>
MYBOXES.description === MYBOXES2.description
</programlisting>
but not for a clause of the form:
<programlisting>
MYBOXES.description <<< MYBOXES2.description.
</programlisting>
The hashes flag gives the needed information to the query
optimizer concerning whether a hash join strategy is
usable for the operator in question.</para>
<para>
Similarly, the two sort operators indicate to the query
optimizer whether merge-sort is a usable join strategy and
what operators should be used to sort the two operand
classes. For the === clause above, the optimizer must
sort both relations using the operator, <<<. On the other
hand, merge-sort is not usable with the clause:
<programlisting>
MYBOXES.description <<< MYBOXES2.description
</programlisting>
</para>
<para>
If other join strategies are found to be practical, Post
gres will change the optimizer and run-time system to use
them and will require additional specification when an
operator is defined. Fortunately, the research community
invents new join strategies infrequently, and the added
generality of user-defined join strategies was not felt to
be worth the complexity involved.
</para>
<para>
The last two pieces of the specification are present so
the query optimizer can estimate result sizes. If a
clause of the form:
<programlisting>
MYBOXES.description <<< "0,0,1,1"::box
</programlisting>
is present in the qualification, then Postgres may have to
estimate the fraction of the instances in MYBOXES that
satisfy the clause. The function res_proc must be a reg
istered function (meaning it is already defined using
define function(l)) which accepts one argument of the correct
data type and returns a floating point number. The
query optimizer simply calls this function, passing the
parameter "0,0,1,1" and multiplies the result by the relation
size to get the desired expected number of instances.
</para>
<para>
Similarly, when the operands of the operator both contain
instance variables, the query optimizer must estimate the
size of the resulting join. The function join_proc will
return another floating point number which will be multiplied
by the cardinalities of the two classes involved to
compute the desired expected result size.
</para>
<para>
The difference between the function
<programlisting>
my_procedure_1 (MYBOXES.description, "0,0,1,1"::box)
</programlisting>
and the operator
<programlisting>
MYBOXES.description === "0,0,1,1"::box
</programlisting>
is that Postgres attempts to optimize operators and can
decide to use an index to restrict the search space when
operators are involved. However, there is no attempt to
optimize functions, and they are performed by brute force.
Moreover, functions can have any number of arguments while
operators are restricted to one or two.
</PARA>
<REFSECT2 ID="R2-SQL-CREATEOPERATOR-3">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Notes
</TITLE>
<PARA>
Refer to <citetitle>PostgreSQL User's Guide</citetitle> chapter 5
<comment>
This reference must be corrected.
</comment>
for further information.
Refer to DROP OPERATOR statement to drop operators.
</REFSECT2>
<REFSECT1 ID="R1-SQL-CREATEOPERATOR-2">
<TITLE>
Usage
</TITLE>
<PARA>The following command defines a new operator,
area-equality, for the BOX data type.
</PARA>
<ProgramListing>
CREATE OPERATOR === (
LEFTARG = box,
RIGHTARG = box,
PROCEDURE = area_equal_procedure,
COMMUTATOR = ===,
NEGATOR = !==,
RESTRICT = area_restriction_procedure,
HASHES,
JOIN = area-join-procedure,
SORT = <<<, <<<)
</ProgramListing>
</REFSECT1>
<REFSECT1 ID="R1-SQL-CREATEOPERATOR-3">
<TITLE>
Compatibility
</TITLE>
<PARA>
CREATE OPERATOR is a PostgreSQL extension of SQL.
</PARA>
<REFSECT2 ID="R2-SQL-CREATEOPERATOR-4">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
SQL92
</TITLE>
<PARA>
There is no CREATE OPERATOR statement on SQL92.
</PARA>
</refsect2>
</refsect1>
</REFENTRY>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"../reference.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:"/usr/lib/sgml/catalog"
sgml-local-ecat-files:nil
End:
-->

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doc/src/sgml/ref/create_rule.sgml Normal file
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<REFENTRY ID="SQL-CREATERULE-1">
<REFMETA>
<REFENTRYTITLE>
CREATE RULE
</REFENTRYTITLE>
<REFMISCINFO>SQL - Language Statements</REFMISCINFO>
</REFMETA>
<REFNAMEDIV>
<REFNAME>
CREATE RULE
</REFNAME>
<REFPURPOSE>
Defines a new rule.
</REFPURPOSE>
<REFSYNOPSISDIV>
<REFSYNOPSISDIVINFO>
<DATE>1998-04-15</DATE>
</REFSYNOPSISDIVINFO>
<SYNOPSIS>
CREATE RULE <replaceable class="parameter">name</replaceable>
AS ON <replaceable class="parameter">event</replaceable>
TO <replaceable class="parameter">object</replaceable> [WHERE <replaceable class="parameter">condition</replaceable>]
DO [INSTEAD]
[<replaceable class="parameter">action</replaceable> | NOTHING ]
</SYNOPSIS>
<REFSECT2 ID="R2-SQL-CREATERULE-1">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Inputs
</TITLE>
<PARA>
</PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
</TERM>
<LISTITEM>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">name</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
The name of a rule to create.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">event</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Event is one of <literal>select</literal>, <literal>update</literal>, <literal>delete</literal> or <literal>insert</literal>.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">object</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Object is either <replaceable class="parameter">table</replaceable> or <replaceable class="parameter">table</replaceable>.<replaceable class="parameter">column</replaceable>.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">condition</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Any SQL <literal>where</literal> clause. <literal>new</literal> or
<literal>current</literal> can appear instead of an instance
variable whenever an instance variable is permissible in SQL.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">action</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Any SQL-statement. <literal>new</literal> or
<literal>current</literal> can appear instead of an instance
variable whenever an instance variable is permissible in SQL.
</PARA>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</REFSECT2>
<REFSECT2 ID="R2-SQL-CREATERULE-2">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Outputs
</TITLE>
<PARA>
</PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
</TERM>
<LISTITEM>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<ReturnValue>CREATE</ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Message returned if the rule is successfully created.
</PARA>
</LISTITEM>
</VARLISTENTRY>
</variablelist>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</REFSECT2>
</REFSYNOPSISDIV>
<REFSECT1 ID="R1-SQL-CREATERULE-1">
<REFSECT1INFO>
<DATE>1998-04-15</DATE>
</REFSECT1INFO>
<TITLE>
Description
</TITLE>
<PARA>
The semantics of a rule is that at the time an individual instance is
accessed, updated, inserted or deleted, there is a current instance (for
retrieves, updates and deletes) and a new instance (for updates and
appends). If the <replaceable class="parameter">event</replaceable>
specified in the <literal>on</literal> clause and the
<replaceable class="parameter">condition</replaceable> specified in the
<literal>where</literal> clause are true for the current instance, the
<replaceable class="parameter">action</replaceable> part of the rule is
executed. First, however, values from fields in the current instance
and/or the new instance are substituted for
<literal> current.</literal><replaceable class="parameter">attribute-name</replaceable>
and <literal>new.</literal><replaceable class="parameter">attribute-name</replaceable>.
</para>
<para>
The <replaceable class="parameter">action</replaceable> part of the rule
executes with the same command and transaction identifier as the user
command that caused activation.
</para>
<REFSECT2 ID="R2-SQL-CREATERULE-3">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Notes
</TITLE>
<para>
A note of caution about SQL rules is in order. If the same class name
or instance variable appears in the
<replaceable class="parameter">event</replaceable>, the
<replaceable class="parameter">condition</replaceable> and the
<replaceable class="parameter">action</replaceable> parts of a rule,
they are all considered different tuple variables. More accurately,
<literal>new</literal> and <literal>current</literal> are the only tuple
variables that are shared between these clauses. For example, the following
two rules have the same semantics:
<programlisting>
on update to EMP.salary where EMP.name = "Joe"
do update EMP ( ... ) where ...
on update to EMP-1.salary where EMP-2.name = "Joe"
do update EMP-3 ( ... ) where ...
</programlisting>
Each rule can have the optional tag <literal>instead</literal>. Without
this tag, <replaceable class="parameter">action</replaceable> will be
performed in addition to the user command when the
<replaceable class="parameter">event</replaceable> in the
<replaceable class="parameter">condition</replaceable> part of the rule
occurs. Alternately, the
<replaceable class="parameter">action</replaceable> part will be done
instead of the user command. In this later case, the
<replaceable class="parameter">action</replaceable> can be the keyword
<literal>nothing</literal>.
</para>
<para>
When choosing between the rewrite and instance rule systems for a
particular rule application, remember that in the rewrite system,
<literal>current</literal> refers to a relation and some qualifiers
whereas in the instance system it refers to an instance (tuple).
</para>
<para>
It is very important to note that the rewrite rule system
will neither detect nor process circular rules. For example, though each
of the following two rule definitions are accepted by Postgres, the
retrieve command will cause Postgres to crash:
<example>
<title>Example of a circular rewrite rule combination.</title>
<programlisting>
create rule bad_rule_combination_1 is
on select to EMP
do instead select to TOYEMP
create rule bad_rule_combination_2 is
on select to TOYEMP
do instead select to EMP
</programlisting>
<para>
This attempt to retrieve from EMP will cause Postgres to crash.
<programlisting>
select * from EMP
</programlisting></para>
</example>
</para>
<para>
You must have rule definition access to a class in order
to define a rule on it (see change acl(l)).
<comment>
There is no manpage change or change_acl. What is intended?
</comment>
</PARA>
</REFSECT2>
</refsect1>
<REFSECT1 ID="R1-SQL-CREATERULE-2">
<TITLE>
Usage
</TITLE>
<PARA>
Make Sam get the same salary adjustment as Joe
<programlisting>
create rule example_1 is
on update EMP.salary where current.name = "Joe"
do update EMP (salary = new.salary)
where EMP.name = "Sam"
</programlisting>
At the time Joe receives a salary adjustment, the event
will become true and Joe's current instance and proposed
new instance are available to the execution routines.
Hence, his new salary is substituted into the action part
of the rule which is subsequently executed. This propagates
Joe's salary on to Sam.
</para>
<para>
Make Bill get Joe's salary when it is accessed
<programlisting>
create rule example_2 is
on select to EMP.salary
where current.name = "Bill"
do instead
select (EMP.salary) from EMP where EMP.name = "Joe"
</programlisting>
</para>
<para>
Deny Joe access to the salary of employees in the shoe
department. (<function>pg_username()</function> returns the name of
the current user)
<programlisting>
create rule example_3 is
on select to EMP.salary
where current.dept = "shoe" and pg_username() = "Joe"
do instead nothing
</programlisting>
</para>
<para>
Create a view of the employees working in the toy department.
<programlisting>
create TOYEMP(name = char16, salary = int4)
create rule example_4 is
on select to TOYEMP
do instead select (EMP.name, EMP.salary) from EMP
where EMP.dept = "toy"
</programlisting>
</para>
<para>
All new employees must make 5,000 or less
<programlisting>
create rule example_5 is
on insert to EMP where new.salary > 5000
do update newset salary = 5000
</programlisting>
</PARA>
</REFSECT1>
<REFSECT1 ID="R1-SQL-CREATERULE-3">
<TITLE>
Bugs
</TITLE>
<PARA>
<literal>instead</literal> rules do not work properly.
</para>
<para>
The object in a SQL rule cannot be an array reference and
cannot have parameters.
</para>
<para>
Aside from the "oid" field, system attributes cannot be
referenced anywhere in a rule. Among other things, this
means that functions of instances (e.g., "<literal>foo(emp)</literal>" where
"<literal>emp</literal>" is a class) cannot be called anywhere in a rule.
</para>
<para>
The rule system stores the rule text and query plans as
text attributes. This implies that creation of rules may
fail if the rule plus its various internal representations
exceed some value that is on the order of one page (8KB).
</PARA>
<REFSECT1 ID="R1-SQL-CREATERULE-4">
<TITLE>
Compatibility
</TITLE>
<PARA>
CREATE RULE statement is a PostgreSQL language extension.
</PARA>
<REFSECT2 ID="R2-SQL-CREATERULE-4">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
SQL92
</TITLE>
<para>
There is no CREATE RULE statement in SQL92.
</para>
</refsect2>
</refsect1>
</REFENTRY>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"../reference.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:"/usr/lib/sgml/catalog"
sgml-local-ecat-files:nil
End:
-->

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<REFENTRY ID="SQL-CREATESEQUENCE-1">
<REFMETA>
<REFENTRYTITLE>
CREATE SEQUENCE
</REFENTRYTITLE>
<REFMISCINFO>SQL - Language Statements</REFMISCINFO>
</REFMETA>
<REFNAMEDIV>
<REFNAME>
CREATE SEQUENCE
</REFNAME>
<REFPURPOSE>
creates a new sequence number generator.
</REFPURPOSE>
<REFSYNOPSISDIV>
<REFSYNOPSISDIVINFO>
<DATE>1998-04-15</DATE>
</REFSYNOPSISDIVINFO>
<SYNOPSIS>
CREATE SEQUENCE <replaceable class="parameter">seqname</replaceable>
[INCREMENT <replaceable class="parameter">increment</replaceable>]
[MINVALUE <replaceable class="parameter">minvalue</replaceable>]
[MAXVALUE <replaceable class="parameter">maxvalue</replaceable>]
[START <replaceable class="parameter">start</replaceable>]
[CACHE <replaceable class="parameter">cache</replaceable>]
[CYCLE]
</SYNOPSIS>
<REFSECT2 ID="R2-SQL-CREATESEQUENCE-1">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Inputs
</TITLE>
<PARA>
</PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
</TERM>
<LISTITEM>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">seqname</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
The name of a sequence to be created.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">increment</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
The <option>INCREMENT <replaceable class="parameter">increment</replaceable></option> clause is optional. A positive value will make an
ascending sequence, a negative one a descending sequence. The default value
is 1.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">minvalue</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
The optional clause <option>MINVALUE
<replaceable class="parameter">minvalue</replaceable></option>
determines the minimum value
a sequence can be. The defaults are 1 and -2147483647 for
ascending and descending sequences, respectively.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">maxvalue</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Use the optional clause <option>MAXVALUE
<replaceable class="parameter">maxvalue</replaceable></option> to
determine the maximum
value for the sequence. The defaults are 2147483647 and -1 for
ascending and descending sequences, respectively.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">start</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
The optional <option>START
<replaceable class="parameter">start</replaceable>
clause</option> enables the sequence to begin anywhere.
The default starting value is
<replaceable class="parameter">minvalue</replaceable>
for ascending sequences and
<replaceable class="parameter">maxvalue</replaceable>
for descending ones.
<comment>
What happens if the user specifies start outside the range?
</comment>
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue><replaceable class="parameter">cache</replaceable></ReturnValue>
</TERM>
<LISTITEM>
<PARA>
The <option>CACHE <replaceable class="parameter">cache</replaceable></option> option
enables sequence numbers to be preallocated
and stored in memory for faster access. The minimum
value is 1 (no cache) and this is also the default.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue>CYCLE</ReturnValue>
</TERM>
<LISTITEM>
<PARA>
The optional CYCLE keyword may be used to enable the sequence
to continue when the
<replaceable class="parameter">maxvalue</replaceable> or
<replaceable class="parameter">minvalue</replaceable> has been
reached by
an ascending or descending sequence respectively. If the limit is
reached, the next number generated will be whatever the
<replaceable class="parameter">minvalue</replaceable> or
<replaceable class="parameter">maxvalue</replaceable> is,
as appropriate.
</PARA>
</LISTITEM>
</VARLISTENTRY>
</variablelist>
</LISTITEM>
</VARLISTENTRY>
</variablelist>
</REFSECT2>
<REFSECT2 ID="R2-SQL-CREATESEQUENCE-2">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Outputs
</TITLE>
<PARA>
</PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
</TERM>
<LISTITEM>
<PARA>
<VARIABLELIST>
<VARLISTENTRY>
<TERM>
<ReturnValue>CREATE</ReturnValue>
</TERM>
<LISTITEM>
<PARA>
Message returned if the command is successful.
</PARA>
</LISTITEM>
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<ReturnValue>ERROR: amcreate: '<replaceable class="parameter"> seqname</replaceable>' relation already exists</ReturnValue>
</TERM>
<LISTITEM>
<PARA>
If the sequence specified already exists.
</PARA>
</LISTITEM>
</VARLISTENTRY>
</variablelist>
</LISTITEM>
</VARLISTENTRY>
</VARIABLELIST>
</REFSECT2>
</REFSYNOPSISDIV>
<REFSECT1 ID="R1-SQL-CREATESEQUENCE-1">
<REFSECT1INFO>
<DATE>1998-04-15</DATE>
</REFSECT1INFO>
<TITLE>
Description
</TITLE>
<PARA>
CREATE SEQUENCE will enter a new sequence number generator
into the current data base. This involves creating and initialising a
new single block
table with the name <replaceable class="parameter">seqname</replaceable>.
The generator will be "owned" by the user issuing the command.
</PARA>
<para>
After the sequence is created, you may use the function
<function>nextval()</function> with the
sequence name as the argument to get a new number from the sequence.
The function <function>currval('<replaceable class="parameter">sequence_name</replaceable>')</function> may be used
to determine the number returned by the last call to
<function>nextval()</function> for the
specified sequence in the current session.
</para>
<para>
Use a query like
<programlisting>
SELECT * FROM sequence_name;
</programlisting>
to get the parameters of a sequence.
</para>
<para>
Low-level locking is used to enable multiple simultaneous
calls to a generator.
</para>
<REFSECT2 ID="R2-SQL-CREATESEQUENCE-3">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
Notes
</TITLE>
<PARA>
Refer to the DROP SEQUENCE statement to remove a sequence.
</PARA>
<para>
Each backend uses its own cache to store allocated numbers.
Numbers that are cached but not used in the current session will be
lost.
</para>
</REFSECT2>
</refsect1>
<REFSECT1 ID="R1-SQL-CREATESEQUENCE-2">
<TITLE>
Usage
</TITLE>
<PARA>
Create an ascending sequence called serial, starting at 101:
</PARA>
<ProgramListing>
CREATE SEQUENCE serial START 101;
</ProgramListing>
<para>
Select the next number from this sequence
<programlisting>
SELECT NEXTVAL ('serial');
nextval
-------
114
</programlisting>
</para>
<para>
Use this sequence in an INSERT:
<programlisting>
INSERT INTO distributors VALUES (NEXTVAL ('serial'),'nothing');
</programlisting>
</para>
</REFSECT1>
<REFSECT1 ID="R1-SQL-CREATESEQUENCE-3">
<TITLE>
Compatibility
</TITLE>
<PARA>
CREATE SEQUENCE statement is a PostgreSQL language extension.
</PARA>
<REFSECT2 ID="R2-SQL-CREATESEQUENCE-4">
<REFSECT2INFO>
<DATE>1998-04-15</DATE>
</REFSECT2INFO>
<TITLE>
SQL92
</TITLE>
<PARA>
There is no CREATE SEQUENCE statement on SQL92.
</PARA>
</refsect2>
</refsect1>
</REFENTRY>
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