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diff --git a/doc/src/sgml/ref/create_sequence.sgml b/doc/src/sgml/ref/create_sequence.sgml index 8e5ca32962c..374f34cb0a8 100644 --- a/doc/src/sgml/ref/create_sequence.sgml +++ b/doc/src/sgml/ref/create_sequence.sgml @@ -1,5 +1,5 @@ <!-- -$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_sequence.sgml,v 1.32 2003/03/25 16:15:39 petere Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_sequence.sgml,v 1.33 2003/04/22 10:08:08 petere Exp $ PostgreSQL documentation --> @@ -8,248 +8,36 @@ PostgreSQL documentation <refentrytitle id="sql-createsequence-title">CREATE SEQUENCE</refentrytitle> <refmiscinfo>SQL - Language Statements</refmiscinfo> </refmeta> + <refnamediv> - <refname> - CREATE SEQUENCE - </refname> - <refpurpose> - define a new sequence generator - </refpurpose> + <refname>CREATE SEQUENCE</refname> + <refpurpose>define a new sequence generator</refpurpose> </refnamediv> + <refsynopsisdiv> - <refsynopsisdivinfo> - <date>1999-07-20</date> - </refsynopsisdivinfo> - <synopsis> +<synopsis> CREATE [ TEMPORARY | TEMP ] SEQUENCE <replaceable class="parameter">seqname</replaceable> [ INCREMENT [ BY ] <replaceable class="parameter">increment</replaceable> ] [ MINVALUE <replaceable class="parameter">minvalue</replaceable> | NO MINVALUE ] [ MAXVALUE <replaceable class="parameter">maxvalue</replaceable> | NO MAXVALUE ] [ START [ WITH ] <replaceable class="parameter">start</replaceable> ] [ CACHE <replaceable class="parameter">cache</replaceable> ] [ [ NO ] CYCLE ] - </synopsis> - - <refsect2 id="R2-SQL-CREATESEQUENCE-1"> - <refsect2info> - <date>1998-09-11</date> - </refsect2info> - <title> - Inputs - </title> - <para> - - <variablelist> - <varlistentry> - <term>TEMPORARY or TEMP</term> - <listitem> - <para> - If specified, the sequence object is created only for this session, - and is automatically dropped on session exit. - Existing permanent sequences with the same name are not visible - (in this session) while the temporary sequence exists, unless - they are referenced with schema-qualified names. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="parameter">seqname</replaceable></term> - <listitem> - <para> - The name (optionally schema-qualified) of a sequence to be created. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="parameter">increment</replaceable></term> - <listitem> - <para> - The - <option>INCREMENT BY <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 one (1). - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="parameter">minvalue</replaceable></term> - <term>NO MINVALUE</term> - <listitem> - <para> - The optional clause <option>MINVALUE - <replaceable class="parameter">minvalue</replaceable></option> - determines the minimum value - a sequence can generate. If this clause is not supplied or <option>NO MINVALUE</option> - is specified, then defaults will be used. The defaults are 1 and -2^63-1 for - ascending and descending sequences, respectively. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="parameter">maxvalue</replaceable></term> - <term>NO MAXVALUE</term> - <listitem> - <para> - The optional clause <option>MAXVALUE - <replaceable class="parameter">maxvalue</replaceable></option> - determines the maximum - value for the sequence. If this clause is not supplied or - <option>NO MAXVALUE</option> is specified, then default values will be used. - The defaults are 2^63-1 and -1 for ascending and descending sequences, respectively. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="parameter">start</replaceable></term> - <listitem> - <para> - The optional <option>START WITH - <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. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="parameter">cache</replaceable></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 (only one value can be generated at a time, i.e., no cache) - and this is also the default. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term>CYCLE</term> - <listitem> - <para> - The optional <option>CYCLE</option> keyword may be used to enable - the sequence to wrap around 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 the - <replaceable class="parameter">minvalue</replaceable> or - <replaceable class="parameter">maxvalue</replaceable>, - respectively. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term>NO CYCLE</term> - <listitem> - <para> - If the optional <option>NO CYCLE</option> keyword is specified, any - calls to <function>nextval</function> after the sequence has reached - its maximum value will return an error. If neither - <option>CYCLE</option> or <option>NO CYCLE</option> are specified, - <option>NO CYCLE</option> is the default. - </para> - </listitem> - </varlistentry> - </variablelist> - </para> - </refsect2> - - <refsect2 id="R2-SQL-CREATESEQUENCE-2"> - <refsect2info> - <date>1998-09-11</date> - </refsect2info> - <title> - Outputs - </title> - <para> - - <variablelist> - <varlistentry> - <term><computeroutput> -CREATE SEQUENCE - </computeroutput></term> - <listitem> - <para> - Message returned if the command is successful. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><computeroutput> -ERROR: Relation '<replaceable class="parameter">seqname</replaceable>' already exists - </computeroutput></term> - <listitem> - <para> - If the sequence specified already exists. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><computeroutput> -ERROR: DefineSequence: MINVALUE (<replaceable class="parameter">start</replaceable>) can't be >= MAXVALUE (<replaceable class="parameter">max</replaceable>) - </computeroutput></term> - <listitem> - <para> - If the specified starting value is out of range. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><computeroutput> -ERROR: DefineSequence: START value (<replaceable class="parameter">start</replaceable>) can't be < MINVALUE (<replaceable class="parameter">min</replaceable>) - </computeroutput></term> - <listitem> - <para> - If the specified starting value is out of range. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><computeroutput> -ERROR: DefineSequence: MINVALUE (<replaceable class="parameter">min</replaceable>) can't be >= MAXVALUE (<replaceable class="parameter">max</replaceable>) - </computeroutput></term> - <listitem> - <para> - If the minimum and maximum values are inconsistent. - </para> - </listitem> - </varlistentry> - </variablelist> - </para> - </refsect2> +</synopsis> </refsynopsisdiv> - <refsect1 id="R1-SQL-CREATESEQUENCE-1"> - <refsect1info> - <date>1998-09-11</date> - </refsect1info> - <title> - Description - </title> + <refsect1> + <title>Description</title> + <para> - <command>CREATE SEQUENCE</command> will enter a new sequence number generator - into the current database. This involves creating and initializing a - new single-row - table with the name <replaceable class="parameter">seqname</replaceable>. - The generator will be owned by the user issuing the command. + <command>CREATE SEQUENCE</command> creates a new sequence number + generator. This involves creating and initializing a new special + single-row table with the name <replaceable + class="parameter">seqname</replaceable>. The generator will be + owned by the user issuing the command. </para> <para> If a schema name is given then the sequence is created in the - specified schema. Otherwise it is created in the current schema (the one - at the front of the search path; see <literal>CURRENT_SCHEMA()</>). - TEMP sequences exist in a special schema, so a schema name may not be - given when creating a TEMP sequence. + specified schema. Otherwise it is created in the current schema. + Temporary sequences exist in a special schema, so a schema name may not be + given when creating a temporary sequence. The sequence name must be distinct from the name of any other sequence, table, index, or view in the same schema. </para> @@ -257,7 +45,7 @@ ERROR: DefineSequence: MINVALUE (<replaceable class="parameter">min</replaceabl <para> After a sequence is created, you use the functions <function>nextval</function>, - <function>currval</function> and + <function>currval</function>, and <function>setval</function> to operate on the sequence. These functions are documented in <xref linkend="functions-sequence">. @@ -266,132 +54,293 @@ ERROR: DefineSequence: MINVALUE (<replaceable class="parameter">min</replaceabl <para> Although you cannot update a sequence directly, you can use a query like - <programlisting> +<programlisting> SELECT * FROM <replaceable>seqname</replaceable>; - </programlisting> +</programlisting> to examine the parameters and current state of a sequence. In particular, the <literal>last_value</> field of the sequence shows the last value - allocated by any backend process. (Of course, this value may be obsolete - by the time it's printed, if other processes are actively doing + allocated by any session. (Of course, this value may be obsolete + by the time it's printed, if other sessions are actively doing <function>nextval</> calls.) </para> + </refsect1> + + <refsect1> + <title>Parameters</title> + + <variablelist> + <varlistentry> + <term><literal>TEMPORARY</literal> or <literal>TEMP</literal></term> + <listitem> + <para> + If specified, the sequence object is created only for this + session, and is automatically dropped on session exit. Existing + permanent sequences with the same name are not visible (in this + session) while the temporary sequence exists, unless they are + referenced with schema-qualified names. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><replaceable class="parameter">seqname</replaceable></term> + <listitem> + <para> + The name (optionally schema-qualified) of the sequence to be created. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><replaceable class="parameter">increment</replaceable></term> + <listitem> + <para> + The optional clause <literal>INCREMENT BY <replaceable + class="parameter">increment</replaceable></literal> specified, + which value is added to the current sequence value to create a + new value. A positive value will make an ascending sequence, a + negative one a descending sequence. The default value is 1. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><replaceable class="parameter">minvalue</replaceable></term> + <term><literal>NO MINVALUE</literal></term> + <listitem> + <para> + The optional clause <literal>MINVALUE <replaceable + class="parameter">minvalue</replaceable></literal> determines + the minimum value a sequence can generate. If this clause is not + supplied or <option>NO MINVALUE</option> is specified, then + defaults will be used. The defaults are 1 and + -2<superscript>63</>-1 for ascending and descending sequences, + respectively. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><replaceable class="parameter">maxvalue</replaceable></term> + <term><literal>NO MAXVALUE</literal></term> + <listitem> + <para> + The optional clause <literal>MAXVALUE <replaceable + class="parameter">maxvalue</replaceable></literal> determines + the maximum value for the sequence. If this clause is not + supplied or <option>NO MAXVALUE</option> is specified, then + default values will be used. The defaults are + 2<superscript>63</>-1 and -1 for ascending and descending + sequences, respectively. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><replaceable class="parameter">start</replaceable></term> + <listitem> + <para> + The optional clause <literal>START WITH <replaceable + class="parameter">start</replaceable> </literal> allows 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. + </para> + </listitem> + </varlistentry> - <caution> - <para> - Unexpected results may be obtained if a <replaceable class="parameter">cache</replaceable> setting greater than one - is used for a sequence object that will be used concurrently by multiple - backends. Each backend will allocate and cache successive sequence values - during one access to the sequence object and increase the sequence - object's <literal>last_value</> accordingly. Then, the next <replaceable class="parameter">cache</replaceable>-1 uses of <function>nextval</> - within that backend simply return the preallocated values without touching - the shared object. So, any numbers allocated but not used within a session - will be lost when that session ends. Furthermore, although multiple backends are guaranteed to - allocate distinct sequence values, the values may be generated out of - sequence when all the backends are considered. (For example, with a <replaceable class="parameter">cache</replaceable> - setting of 10, backend A might reserve values 1..10 and return <function>nextval</function>=1, - then - backend B might reserve values 11..20 and return <function>nextval</function>=11 before backend - A has generated <literal>nextval</literal>=2.) Thus, with a <replaceable class="parameter">cache</replaceable> setting of one it is safe - to assume that <function>nextval</> values are generated sequentially; with a <replaceable class="parameter">cache</replaceable> - setting greater than one you should only assume that the <function>nextval</> values - are all distinct, not that they are generated purely sequentially. - Also, <literal>last_value</> will reflect the latest value reserved by any backend, - whether or not it has yet been returned by <function>nextval</>. - Another consideration is that a <function>setval</> executed on such a sequence - will not be noticed by other backends until they have used up any - preallocated values they have cached. - </para> - </caution> - - <refsect2 id="R2-SQL-CREATESEQUENCE-3"> - <refsect2info> - <date>1998-09-11</date> - </refsect2info> - <title> - Notes - </title> - - <para> - Use <command>DROP SEQUENCE</command> to remove a sequence. - </para> - - <para> - Sequences are based on <type>bigint</> arithmetic, so the range cannot - exceed the range of an eight-byte integer - (-9223372036854775808 to 9223372036854775807). On some older platforms, - there may be no compiler support for eight-byte integers, in which case - sequences use regular <type>integer</> arithmetic (range - -2147483648 to +2147483647). - </para> - - <para> - When <replaceable class="parameter">cache</replaceable> is greater than - one, each backend uses its own cache to store preallocated numbers. - Numbers that are cached but not used in the current session will be - lost, resulting in <quote>holes</quote> in the sequence. - </para> - </refsect2> + <varlistentry> + <term><replaceable class="parameter">cache</replaceable></term> + <listitem> + <para> + The optional clause <literal>CACHE <replaceable + class="parameter">cache</replaceable></literal> specifies how + many sequence numbers are to be preallocated and stored in + memory for faster access. The minimum value is 1 (only one value + can be generated at a time, i.e., no cache), and this is also the + default. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><literal>CYCLE</literal></term> + <term><literal>NO CYCLE</literal></term> + <listitem> + <para> + The <literal>CYCLE</literal> option allows the sequence to wrap + around 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 the <replaceable + class="parameter">minvalue</replaceable> or <replaceable + class="parameter">maxvalue</replaceable>, respectively. + </para> + + <para> + If <literal>NO CYCLE</literal> is specified, any calls to + <function>nextval</function> after the sequence has reached its + maximum value will return an error. If neither + <literal>CYCLE</literal> or <literal>NO CYCLE</literal> are + specified, <literal>NO CYCLE</literal> is the default. + </para> + </listitem> + </varlistentry> + </variablelist> </refsect1> - <refsect1 id="R1-SQL-CREATESEQUENCE-2"> - <title> - Usage - </title> + <refsect1> + <title>Diagnostics</title> + + <variablelist> + <varlistentry> + <term><computeroutput>CREATE SEQUENCE</computeroutput></term> + <listitem> + <para> + Message returned if the sequence was successfully created. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><computeroutput>ERROR: Relation '<replaceable class="parameter">seqname</replaceable>' already exists</computeroutput></term> + <listitem> + <para> + A sequence, table, view, or index of the specified name already exists. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><computeroutput>ERROR: DefineSequence: MINVALUE (<replaceable class="parameter">start</replaceable>) can't be >= MAXVALUE (<replaceable class="parameter">max</replaceable>)</computeroutput></term> + <term><computeroutput>ERROR: DefineSequence: START value (<replaceable class="parameter">start</replaceable>) can't be < MINVALUE (<replaceable class="parameter">min</replaceable>)</computeroutput></term> + <listitem> + <para> + The specified starting value is out of range. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><computeroutput>ERROR: DefineSequence: MINVALUE (<replaceable class="parameter">min</replaceable>) can't be >= MAXVALUE (<replaceable class="parameter">max</replaceable>)</computeroutput></term> + <listitem> + <para> + The minimum and maximum values are inconsistent. + </para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Notes</title> + <para> - Create an ascending sequence called <literal>serial</literal>, starting at 101: + Use <command>DROP SEQUENCE</command> to remove a sequence. + </para> + + <para> + Sequences are based on <type>bigint</> arithmetic, so the range + cannot exceed the range of an eight-byte integer + (-9223372036854775808 to 9223372036854775807). On some older + platforms, there may be no compiler support for eight-byte + integers, in which case sequences use regular <type>integer</> + arithmetic (range -2147483648 to +2147483647). + </para> + + <para> + Unexpected results may be obtained if a <replaceable + class="parameter">cache</replaceable> setting greater than one is + used for a sequence object that will be used concurrently by + multiple sessions. Each session will allocate and cache successive + sequence values during one access to the sequence object and + increase the sequence object's <literal>last_value</> accordingly. + Then, the next <replaceable class="parameter">cache</replaceable>-1 + uses of <function>nextval</> within that session simply return the + preallocated values without touching the sequence object. So, any + numbers allocated but not used within a session will be lost when + that session ends, resulting in <quote>holes</quote> in the + sequence. + </para> + + <para> + Furthermore, although multiple sessions are guaranteed to allocate + distinct sequence values, the values may be generated out of + sequence when all the sessions are considered. FFor example, with + a <replaceable class="parameter">cache</replaceable> setting of 10, + session A might reserve values 1..10 and return + <function>nextval</function>=1, then session B might reserve values + 11..20 and return <function>nextval</function>=11 before session A + has generated <literal>nextval</literal>=2. Thus, with a + <replaceable class="parameter">cache</replaceable> setting of one + it is safe to assume that <function>nextval</> values are generated + sequentially; with a <replaceable + class="parameter">cache</replaceable> setting greater than one you + should only assume that the <function>nextval</> values are all + distinct, not that they are generated purely sequentially. Also, + <literal>last_value</> will reflect the latest value reserved by + any session, whether or not it has yet been returned by + <function>nextval</>. + </para> + + <para> + Another consideration is that a <function>setval</> executed on + such a sequence will not be noticed by other sessions until they + have used up any preallocated values they have cached. </para> - <programlisting> + </refsect1> + + <refsect1> + <title>Examples</title> + + <para> + Create an ascending sequence called <literal>serial</literal>, starting at 101: +<programlisting> CREATE SEQUENCE serial START 101; - </programlisting> +</programlisting> + </para> + <para> Select the next number from this sequence: - <programlisting> +<programlisting> SELECT nextval('serial'); -nextval -------- - 114 - </programlisting> + nextval +--------- + 114 +</programlisting> </para> + <para> - Use this sequence in an INSERT: - <programlisting> + Use this sequence in an <command>INSERT</command> command: +<programlisting> INSERT INTO distributors VALUES (nextval('serial'), 'nothing'); - </programlisting> +</programlisting> </para> <para> - Update the sequence value after a COPY FROM: - <programlisting> + Update the sequence value after a <command>COPY FROM</command>: +<programlisting> BEGIN; - COPY distributors FROM 'input_file'; - SELECT setval('serial', max(id)) FROM distributors; +COPY distributors FROM 'input_file'; +SELECT setval('serial', max(id)) FROM distributors; END; - </programlisting> +</programlisting> </para> </refsect1> - <refsect1 id="R1-SQL-CREATESEQUENCE-3"> - <title> - Compatibility - </title> - - <refsect2 id="R2-SQL-CREATESEQUENCE-4"> - <refsect2info> - <date>1998-09-11</date> - </refsect2info> - <title> - SQL92 - </title> - - <para> - <command>CREATE SEQUENCE</command> is a <productname>PostgreSQL</productname> - language extension. - There is no <command>CREATE SEQUENCE</command> statement - in <acronym>SQL92</acronym>. - </para> - </refsect2> + <refsect1> + <title>Compatibility</title> + + <para> + <command>CREATE SEQUENCE</command> is a + <productname>PostgreSQL</productname> language extension. There is + no <command>CREATE SEQUENCE</command> statement in the SQL + standard. + </para> </refsect1> </refentry> |