DECLAREcursorname [ BINARY ] [ INSENSITIVE ] [ SCROLL ] CURSOR FORquery [ FOR { READ ONLY | UPDATE [ OFcolumn [, ...] ] ]The name of the cursor to be used in subsequent FETCH operations.
Causes the cursor to fetch data in binary rather than in text format.
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.
Column(s) to be updated. Since cursor updates are not currently supported inPostgreSQL the UPDATE clause provokes an informational error message.
The message returned if the SELECT is run successfully.
This message is reported if the same cursor name was already declared in the current transaction block. The previous definition is discarded.
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 usingFETCH.
Normal cursors return data in text format, either ASCII or another encoding scheme depending on how thePostgreSQL 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 of1 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 aspsql 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 toBEGIN,COMMIT andROLLBACK to define a transaction block.
InSQL92 cursors are only available in embeddedSQL (ESQL) applications. ThePostgreSQL backend does not implement an explicitOPEN cursor statement; a cursor is considered to be open when it is declared. However,ecpg, the embedded SQL preprocessor forPostgreSQL, supports theSQL92 cursor conventions, including those involving DECLARE and OPEN statements.