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authorThomas G. Lockhart <lockhart@fourpalms.org>1999-08-08 15:21:50 +0000
committerThomas G. Lockhart <lockhart@fourpalms.org>1999-08-08 15:21:50 +0000
commita76ad509fef621719abb95fedb526e9a0092a312 (patch)
tree1a5295dbdce9296f23f252898aea402f411e7d23 /src/man/create_sequence.l
parentd0a1919852b8c98f43f2795c23690024707fc1e5 (diff)
Remove old man pages. All info is in new man pages or other docs.
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-.\" This is -*-nroff-*-
-.\" XXX standard disclaimer belongs here....
-.\" $Header: /cvsroot/pgsql/src/man/Attic/create_sequence.l,v 1.6 1998/08/30 21:03:19 scrappy Exp $
-.TH "CREATE SEQUENCE" SQL 07/13/98 PostgreSQL PostgreSQL
-.SH NAME
-create sequence - create a new sequence number generator
-.SH SYNOPSIS
-.nf
-\fBcreate sequence\fR seqname
- [\fBincrement\fP incby_value]
- [\fBminvalue\fP min_value]
- [\fBmaxvalue\fP max_value]
- [\fBstart\fP start_value]
- [\fBcache\fP cache_value]
- [\fBcycle\fP]
-.fi
-.SH DESCRIPTION
-.BR "Create sequence"
-will enter a new sequence number generator into the current data base.
-Actually, a new single-record
-.BR table
-with name
-.IR seqname
-will be created and initialized.
-The generator will be
-\*(lqowned\*(rq by the user issuing the command.
-.PP
-The
-.BR increment
-clause is optional. A positive value will make an ascending sequence,
-negative - descending. Default value is 1.
-.PP
-The optional integer
-.BR minvalue
-determines the minimum value the sequence can generate. Defaults are
-1/-2147483647 for ascending/descending sequences.
-.PP
-The optional integer
-.BR maxvalue
-determines the maximum value the sequence can generate. Defaults are
-2147483647/-1 for ascending/descending sequences.
-.PP
-The optional
-.BR start
-value sets the first value to be generated. Default is
-.BR minvalue
-for ascending sequences and
-.BR maxvalue
-for descending ones.
-.PP
-The
-.BR cache
-option enables sequence numbers to be preallocated and
-stored in memory for faster access. The minimum value is 1
-(one value will be allocated at a time, i.e., no cache)
-and that is the default. See below for details.
-.PP
-The optional
-.BR cycle
-keyword may be used to enable the sequence to continue after the
-.BR maxvalue/minvalue
-has been reached by ascending/descending sequence.
-If the limit is reached, the next number generated will be
-whatever the
-.BR minvalue/maxvalue
-is.
-.PP
-After a sequence object has been created, you may use the function
-.BR nextval
-with the sequence name as argument to generate a new number from the
-specified sequence.
-.PP
-The function
-.BR currval
-('sequence_name')
-may be used to re-fetch the number returned by the last call to
-.BR nextval
-for the specified sequence in the current session.
-.BR NOTE:
-currval will return an error if nextval has never been called for the
-given sequence in the current backend session. Also beware that it
-does not give the last number ever allocated, only the last one allocated
-by this backend.
-.PP
-The function
-.BR setval
-('sequence_name', value)
-may be used to set the current value of the specified sequence.
-The next call to
-.BR nextval
-will return the given value + the sequence increment.
-.PP
-Use a query like
-.nf
-SELECT * FROM <sequence_name>;
-.fi
-to get the parameters of a sequence. Aside from fetching the original
-parameters, you can use
-.nf
-SELECT last_value FROM <sequence_name>;
-.fi
-to obtain the last value allocated by any backend.
-.PP
-Low-level locking is used to ensure that multiple backends can safely use
-a sequence object concurrently.
-.PP
-.BR NOTE:
-Unexpected results may be obtained if a cache setting greater than one
-is used for a sequence object that will be used concurrently by multiple
-backends. Each backend will allocate "cache" successive sequence values
-during one access to the sequence object and increase the sequence
-object's last_value accordingly. Then, the next cache-1 uses of nextval
-within that backend simply return the preallocated values without touching
-the shared object. So, numbers allocated but not used in the current session
-will be lost. 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 cache
-setting of 10, backend A might reserve values 1..10 and return nextval=1, then
-backend B might reserve values 11..20 and return nextval=11 before backend
-A has generated nextval=2.) Thus, with a cache setting of one it is safe
-to assume that nextval values are generated sequentially; with a cache
-setting greater than one you should only assume that the nextval values
-are all distinct, not that they are generated purely sequentially.
-Also, last_value will reflect the latest value reserved by any backend,
-whether or not it has yet been returned by nextval.
-.PP
-.SH EXAMPLES
-.nf
---
--- Create sequence seq caching 2 numbers, starting with 10
---
-create sequence seq cache 2 start 10;
-.fi
-.nf
---
--- Select next number from sequence
---
-select nextval ('seq');
-.fi
-.nf
---
--- Use sequence in insert
---
-insert into table _table_ values (nextval ('seq'),...);
-.nf
---
--- Set the sequence value after a copy in
---
-create function table_id_max() returns int4
- as 'select max(id) from _table_'
- language 'sql';
-copy _table_ from 'input_file';
-select setval('seq', table_id_max());
-.fi
-.SH "SEE ALSO"
-drop_sequence(l).