Index for Section 5

Alphabetical listing for D

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DECLARE(5)
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 PostgreSQL
       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(5)].

  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 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.

  NOTES

  Cursors are only available in transactions. Use to BEGIN [begin(5)], COMMIT
  [commit(5)] and ROLLBACK [rollback(5)] 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.

Index for Section 5

Alphabetical listing for D

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