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DECLARE(7)				   SQL Commands 			       DECLARE(7)

       DECLARE - define a cursor

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

	      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.

	      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

       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

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

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

	      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 cur-
	      rent 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.

       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 depend-
       ing  on how the PostgreSQL backend was built. Since data is stored natively in binary for-
       mat, 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 convert 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 different 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.

       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 state-

       To declare a cursor:

       DECLARE liahona CURSOR
	   FOR SELECT * FROM films;

       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 informa-
       tion.  All PostgreSQL cursors are read only.  The BINARY keyword is  a  PostgreSQL  exten-

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