Provided by: postgresql-client-8.4_8.4.3-1_i386 bug

NAME

       DECLARE - define a cursor

SYNOPSIS

       DECLARE name [ BINARY ] [ INSENSITIVE ] [ [ NO ] SCROLL ]
           CURSOR [ { WITH | WITHOUT } HOLD ] FOR query

DESCRIPTION

       DECLARE  allows a user to create cursors, which can be used to retrieve
       a small number of rows at a time out of  a  larger  query.   After  the
       cursor is created, rows are fetched from it using FETCH [fetch(7)].

              Note:  This  page  describes usage of cursors at the SQL command
              level.  If you are trying  to  use  cursors  inside  a  PL/pgSQL
              function, the rules are different — see in the documentation.

PARAMETERS

       name   The name of the cursor to be created.

       BINARY Causes  the  cursor to return data in binary rather than in text
              format.

       INSENSITIVE
              Indicates  that  data  retrieved  from  the  cursor  should   be
              unaffected by updates to the table(s) underlying the cursor that
              occur after the cursor is created. In PostgreSQL,  this  is  the
              default  behavior;  so  this  key word has no effect and is only
              accepted for compatibility with the SQL standard.

       SCROLL

       NO SCROLL
              SCROLL specifies that the cursor can be used to retrieve rows in
              a  nonsequential  fashion  (e.g.,  backward). Depending upon the
              complexity of the  query’s  execution  plan,  specifying  SCROLL
              might  impose  a  performance  penalty  on the query’s execution
              time.  NO SCROLL specifies that the cursor  cannot  be  used  to
              retrieve  rows  in  a  nonsequential  fashion. The default is to
              allow  scrolling  in  some  cases;  this  is  not  the  same  as
              specifying SCROLL. See Notes [declare(7)] for details.

       WITH HOLD

       WITHOUT HOLD
              WITH  HOLD  specifies  that  the  cursor can continue to be used
              after the transaction  that  created  it  successfully  commits.
              WITHOUT HOLD specifies that the cursor cannot be used outside of
              the transaction that created it. If  neither  WITHOUT  HOLD  nor
              WITH HOLD is specified, WITHOUT HOLD is the default.

       query  A  SELECT  [select(7)]  or VALUES [values(7)] command which will
              provide the rows to be returned by the cursor.

       The key words BINARY, INSENSITIVE, and SCROLL can appear in any  order.

NOTES

       Normal  cursors  return data in text format, the same as a SELECT would
       produce. The BINARY option specifies that the cursor should return data
       in  binary  format.  This reduces conversion effort for both the server
       and client, at  the  cost  of  more  programmer  effort  to  deal  with
       platform-dependent  binary  data  formats.   As  an example, if a query
       returns a value of one from an integer column, you would get  a  string
       of  1 with a default cursor, whereas with a binary cursor you would get
       a 4-byte field containing the internal representation of the value  (in
       big-endian byte order).

       Binary  cursors  should be used carefully. Many applications, including
       psql, are not prepared to handle binary cursors and expect data to come
       back in the text format.

              Note:  When  the  client application uses the ‘‘extended query’’
              protocol to issue a FETCH command,  the  Bind  protocol  message
              specifies  whether  data  is  to  be retrieved in text or binary
              format.  This choice  overrides  the  way  that  the  cursor  is
              defined. The concept of a binary cursor as such is thus obsolete
              when using extended query protocol — any cursor can  be  treated
              as either text or binary.

       Unless  WITH  HOLD is specified, the cursor created by this command can
       only be used within the current transaction. Thus, DECLARE without WITH
       HOLD  is  useless outside a transaction block: the cursor would survive
       only to the completion of the statement. Therefore  PostgreSQL  reports
       an  error  if  such a command is used outside a transaction block.  Use
       BEGIN [begin(7)] and COMMIT [commit(7)] (or ROLLBACK [rollback(7)])  to
       define a transaction block.

       If  WITH  HOLD is specified and the transaction that created the cursor
       successfully commits,  the  cursor  can  continue  to  be  accessed  by
       subsequent  transactions  in  the  same  session.  (But if the creating
       transaction is aborted, the cursor is removed.) A cursor  created  with
       WITH  HOLD is closed when an explicit CLOSE command is issued on it, or
       the session ends. In the current implementation, the  rows  represented
       by  a  held  cursor  are copied into a temporary file or memory area so
       that they remain available for subsequent transactions.

       WITH HOLD may not be specified when the query includes  FOR  UPDATE  or
       FOR SHARE.

       The  SCROLL option should be specified when defining a cursor that will
       be used to fetch backwards. This  is  required  by  the  SQL  standard.
       However, for compatibility with earlier versions, PostgreSQL will allow
       backward fetches without SCROLL, if the cursor’s query plan  is  simple
       enough  that  no  extra  overhead  is  needed  to  support it. However,
       application developers are  advised  not  to  rely  on  using  backward
       fetches  from  a  cursor  that  has not been created with SCROLL. If NO
       SCROLL is specified, then backward fetches are disallowed in any  case.

       Backward fetches are also disallowed when the query includes FOR UPDATE
       or FOR SHARE; therefore SCROLL may not be specified in this case.

              Caution: Scrollable and WITH HOLD cursors  may  give  unexpected
              results  if  they  invoke  any  volatile  functions  (see in the
              documentation). When a previously fetched row is re-fetched, the
              functions  might  be  re-executed,  perhaps  leading  to results
              different from the first time. One workaround for such cases  is
              to  declare  the  cursor  WITH  HOLD  and commit the transaction
              before reading any rows from it.  This  will  force  the  entire
              output of the cursor to be materialized in temporary storage, so
              that volatile functions are executed exactly once for each  row.

       If  the  cursor’s query includes FOR UPDATE or FOR SHARE, then returned
       rows are locked at the time they are first fetched, in the same way  as
       for  a  regular  SELECT  [select(7)]  command  with  these options.  In
       addition, the returned rows  will  be  the  most  up-to-date  versions;
       therefore these options provide the equivalent of what the SQL standard
       calls a ‘‘sensitive cursor’’. (Specifying INSENSITIVE together with FOR
       UPDATE or FOR SHARE is an error.)

              Caution:

              It  is  generally recommended to use FOR UPDATE if the cursor is
              intended to be used with UPDATE ... WHERE CURRENT OF  or  DELETE
              ...  WHERE  CURRENT OF. Using FOR UPDATE prevents other sessions
              from changing the rows between the time they are fetched and the
              time  they  are  updated. Without FOR UPDATE, a subsequent WHERE
              CURRENT OF command will have no effect if the  row  was  changed
              since the cursor was created.

              Another  reason  to  use  FOR  UPDATE  is  that  without  it,  a
              subsequent WHERE CURRENT OF might fail if the cursor query  does
              not meet the SQL standard’s rules for being ‘‘simply updatable’’
              (in particular, the cursor must reference just one table and not
              use grouping or ORDER BY). Cursors that are not simply updatable
              might work, or might not, depending on plan choice  details;  so
              in the worst case, an application might work in testing and then
              fail in production.

              The main reason not to use FOR UPDATE with WHERE CURRENT  OF  is
              if you need the cursor to be scrollable, or to be insensitive to
              the subsequent updates (that is, continue to show the old data).
              If  this  is  a requirement, pay close heed to the caveats shown
              above.

       The SQL standard only makes provisions for cursors in embedded SQL. The
       PostgreSQL  server  does not implement an OPEN statement for cursors; a
       cursor is considered to be open when it is  declared.   However,  ECPG,
       the embedded SQL preprocessor for PostgreSQL, supports the standard SQL
       cursor  conventions,  including  those  involving  DECLARE   and   OPEN
       statements.

       You  can  see  all  available cursors by querying the pg_cursors system
       view.

EXAMPLES

       To declare a cursor:

       DECLARE liahona CURSOR FOR SELECT * FROM films;

       See FETCH [fetch(7)] for more examples of cursor usage.

COMPATIBILITY

       The SQL standard  says  that  it  is  implementation-dependent  whether
       cursors  are  sensitive to concurrent updates of the underlying data by
       default. In PostgreSQL, cursors are insensitive by default, and can  be
       made  sensitive  by  specifying  FOR  UPDATE.  Other  products may work
       differently.

       The SQL standard allows cursors only in embedded SQL  and  in  modules.
       PostgreSQL permits cursors to be used interactively.

       Binary cursors are a PostgreSQL extension.

SEE ALSO

       CLOSE [close(7)], FETCH [fetch(7)], MOVE [move(7)]