DECLARE(7)							   SQL Commands 							DECLARE(7)

NAME

       DECLARE - define a cursor

SYNOPSIS

       DECLARE cursorname [ BINARY ] [ INSENSITIVE ] [ SCROLL ]
	   CURSOR FOR query
	   [ FOR { READ ONLY | UPDATE [ OF column [, ...] ] ]

   INPUTS
       cursorname
	      The name of the cursor to be used in subsequent FETCH operations.

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

       INSENSITIVE
	      SQL92 keyword indicating that data retrieved from the cursor should be unaffected by updates from other processes or cursors.  Since
	      cursor operations occur within transactions in PostgreSQL this is always the case.  This keyword has no effect.

       SCROLL SQL92 keyword indicating that data may be retrieved in multiple rows per FETCH operation. Since this is  allowed	at  all  times	by
	      PostgreSQL this keyword has no effect.

       query  An  SQL query which will provide the rows to be governed by the cursor.  Refer to the SELECT statement for further information about
	      valid arguments.

       READ ONLY
	      SQL92 keyword indicating that the cursor will be used in a read only mode. Since this is the only cursor access  mode  available	in
	      PostgreSQL this keyword has no effect.

       UPDATE SQL92  keyword  indicating  that the cursor will be used to update tables. Since cursor updates are not currently supported in Post-
	      greSQL this keyword provokes an informational error message.

       column Column(s) to be updated.	Since cursor updates are not currently supported in PostgreSQL the UPDATE clause provokes an informational
	      error message.

   OUTPUTS
       DECLARE CURSOR
	      The message returned if the SELECT is run successfully.

       WARNING: Closing pre-existing portal "cursorname"
	      This  message  is reported if the same cursor name was already declared in the current transaction block. The previous definition is
	      discarded.

       ERROR: DECLARE CURSOR may only be used in begin/end transaction blocks
	      This error occurs if the cursor is not declared within a transaction block.

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. Cursors  can
       return data either in text or in binary format using FETCH [fetch(7)].

       Normal cursors return data in text format, either ASCII or another encoding scheme depending on how the PostgreSQL backend was built. Since
       data is stored natively in binary format, the system must do a conversion to produce the text format. In addition, text formats	are  often
       larger in size than the corresponding binary format.  Once the information comes back in text form, the client application may need to con-
       vert it to a binary format to manipulate it.  BINARY cursors give you back the data in the native binary representation.

       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 value equal to control-A (^A).

       BINARY  cursors	should be used carefully. User applications such as psql are not aware of binary cursors and expect data to come back in a
       text format.

       String representation is architecture-neutral whereas binary representation can differ between different machine architectures.	PostgreSQL
       does  not resolve byte ordering or representation issues for binary cursors.  Therefore, if your client machine and server machine use dif-
       ferent representations (e.g., ``big-endian'' versus ``little-endian''), you will probably not want your data  returned  in  binary  format.
       However, binary cursors may be a little more efficient since there is less conversion overhead in the server to client data transfer.

	      Tip: If you intend to display the data in ASCII, getting it back in ASCII will save you some effort on the client side.

   NOTES
       Cursors	are only available in transactions. Use to BEGIN [begin(7)], COMMIT [commit(7)] and ROLLBACK [rollback(7)] to define a transaction
       block.

       In SQL92 cursors are only available in embedded SQL (ESQL) applications.  The PostgreSQL backend does not implement an explicit OPEN cursor
       statement;  a  cursor  is considered to be open when it is declared.  However, ecpg, the embedded SQL preprocessor for PostgreSQL, supports
       the SQL92 cursor conventions, including those involving DECLARE and OPEN statements.

USAGE

       To declare a cursor:

       DECLARE liahona CURSOR
	   FOR SELECT * FROM films;

COMPATIBILITY

   SQL92
       SQL92 allows cursors only in embedded SQL and in modules. PostgreSQL permits cursors to be used interactively.  SQL92  allows  embedded	or
       modular cursors to update database information.	All PostgreSQL cursors are read only.  The BINARY keyword is a PostgreSQL extension.

SQL - Language Statements					    2002-11-22								DECLARE(7)