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<chapter id="functions">

<title>Functions and Operators</title>

<listitem>

<para>

Reset the sequence object's counter value. The two-parameter

form sets the sequence's <literal>last_value</literal> field to the specified

value and sets its <literal>is_called</literal> field to <literal>true</literal>,

meaning that the next <function>nextval</function> will advance the sequence

before returning a value. In the three-parameter form,

<literal>is_called</literal> can be set either <literal>true</literal> or

<literal>false</literal>. If it's set to <literal>false</literal>,

the next <function>nextval</function> will return exactly the specified

form sets the sequence's <literal>last_value</literal> field to the

specified value and sets its <literal>is_called</literal> field to

<literal>true</literal>, meaning that the next

<function>nextval</function> will advance the sequence before

returning a value. The value reported by <function>currval</> is

also set to the specified value. In the three-parameter form,

<literal>is_called</literal> can be set either <literal>true</literal>

or <literal>false</literal>. <literal>true</> has the same effect as

the two-parameter form. If it's set to <literal>false</literal>, the

next <function>nextval</function> will return exactly the specified

value, and sequence advancement commences with the following

<function>nextval</function>. For example,

<function>nextval</function>. Furthermore, the value reported by

<function>currval</> is not changed in this case (this is a change

from pre-8.3 behavior). For example,

<screen>

SELECT setval('foo', 42); <lineannotation>Next <function>nextval</> will return 43</lineannotation>

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PostgreSQL documentation

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<para>

The optional clause <literal>RESTART WITH <replaceable

class="parameter">start</replaceable></literal> changes the

current value of the sequence.

current value of the sequence. This is equivalent to calling the

<function>setval</> function with <literal>is_called</literal> =

<literal>false</>: the specified value will be returned by the

<emphasis>next</> call of <function>nextval</>.

</para>

</listitem>

</varlistentry>

immediately.

</para>

<para>

<command>ALTER SEQUENCE</command> does not affect the <function>currval</>

status for the sequence. (Before <productname>PostgreSQL</productname>

8.3, it sometimes did.)

</para>

<para>

Some variants of <command>ALTER TABLE</command> can be used with

sequences as well; for example, to rename a sequence it is also

structSeqTableData*next;/* link to next SeqTable object */

Oidrelid;/* pg_class OID of this sequence */

LocalTransactionIdlxid;/* xact in which we last did a seq op */

boollast_valid;/* do we have a valid "last" value? */

int64last;/* value last returned by nextval */

int64cached;/* last value already cached for nextval */

int64increment;/* copy of sequence's increment field */

}SeqTableData;

typedefSeqTableData*SeqTable;

init_params(stmt->options, false,&new,&owned_by);

elm->cached=elm->last;

memcpy(seq,&new,sizeof(FormData_pg_sequence));

elm->last=new.last_value;/* last returned number */

elm->cached=new.last_value;/* last cached number (forget cached

START_CRIT_SECTION();

MarkBufferDirty(buf);

if (elm->last!=elm->cached)/* some numbers were cached */

{

last_used_seq=elm;

Assert(elm->last_valid);

Assert(elm->increment!=0);

elm->last+=elm->increment;

relation_close(seqrel,NoLock);

last_used_seq=elm;

returnelm->last;

}

elm->last=result;/* last returned number */

elm->cached=last;/* last fetched number */

elm->last_valid= true;

last_used_seq=elm;

errmsg("permission denied for sequence %s",

RelationGetRelationName(seqrel))));

if (elm->increment==0)/* nextval/read_info were not called */

if (!elm->last_valid)

ereport(ERROR,

(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),

errmsg("currval of sequence \"%s\" is not yet defined in this session",

seqrel=open_share_lock(last_used_seq);

Assert(last_used_seq->increment!=0);

Assert(last_used_seq->last_valid);

if (pg_class_aclcheck(last_used_seq->relid,GetUserId(),ACL_SELECT)!=ACLCHECK_OK&&

pg_class_aclcheck(last_used_seq->relid,GetUserId(),ACL_USAGE)!=ACLCHECK_OK)

bufm,bufx)));

}

elm->last=next;/* last returned number */

elm->cached=next;/* last cached number (forget cached values) */

if (iscalled)

{

elm->last=next;/* last returned number */

elm->last_valid= true;

}

elm->cached=elm->last;

START_CRIT_SECTION();

errmsg("out of memory")));

elm->relid=relid;

elm->lxid=InvalidLocalTransactionId;

elm->last=elm->cached=elm->increment=0;

elm->next=seqtab;

seqtab=elm;

seq= (Form_pg_sequence)GETSTRUCT(&tuple);

elm->increment=seq->increment_by;

returnseq;