Opens a previously declared cursor to access information from the database.
Syntax 1 [ESQL]OPEN cursor-name [ USING { DESCRIPTOR sqlda-name | hostvar, ... } ] [ WITH HOLD ] [ ISOLATION LEVEL isolation-level ] [ BLOCK n ]
Syntax 2 [SP]OPEN cursor-name [ WITH HOLD ] [ ISOLATION LEVEL isolation-level ]
cursor-name : identifier | hostvar
sqlda-name : identifier
isolation-level : 0 | 1 | 2 | 3 | SNAPSHOT | STATEMENT SNAPSHOT | READONLY STATEMENT SNAPSHOT
ParametersUSING DESCRIPTOR clause The USING DESCRIPTOR clause is for embedded SQL only. It specifies the host variables to be bound to the placeholder bind variables in the SELECT statement for which the cursor has been declared.
OPEN...USING cannot be used in a stored procedure.
WITH HOLD clause By default, all cursors are automatically closed at the end of the current transaction (COMMIT or ROLLBACK). The optional WITH HOLD clause keeps the cursor open for subsequent transactions. It remains open until the end of the current connection or until an explicit CLOSE statement is executed. Cursors are automatically closed when a connection is terminated.
Upon COMMIT or ROLLBACK, all long-term row locks held by the connection are released, including those rows that constitute the result set of a WITH HOLD cursor. However, cursor stability locks, which are acquired at isolation levels 1, 2, and 3, are retained for the life of the cursor and are only released when the cursor is closed or when the connection terminates.
Upon completion of a ROLLBACK statement, the contents of, and positioning within, a WITH HOLD cursor are unpredictable and are not guaranteed. You can use the ansi_close_cursors_on_rollback option to control whether or not a ROLLBACK statement will close WITH HOLD cursors automatically.
ISOLATION LEVEL clause The ISOLATION LEVEL clause allows this cursor to be opened at an isolation level different from the current setting of the isolation_level option. All operations on this cursor are performed at the specified isolation level regardless of the option setting. If this clause is not specified, then the cursor's isolation level for the entire time the cursor is open is the value of the isolation_level option when the cursor is opened.
The following values are supported:
The cursor is positioned before the first row.
BLOCK clause This clause is for embedded SQL use only. Rows may be fetched by the client application more than one at a time. This is referred to as block fetching, prefetching, or multi-row fetching. The BLOCK clause can reduce the number of rows prefetched. Specifying the BLOCK clause on OPEN is the same as specifying the BLOCK clause on each FETCH.
RemarksThe OPEN statement opens the named cursor. The cursor must be previously declared.
The OPEN statement may return a SQL warning if the cursor type does not match the characteristics of the cursor's underlying statement.
When the cursor is on a CALL statement, OPEN causes the procedure to execute until the first result set (SELECT statement with no INTO clause) is encountered. If the procedure completes and no result set is found, the SQLSTATE_PROCEDURE_COMPLETE warning is set.
Embedded SQL usage After successful execution of the OPEN statement, the sqlerrd[3] field of the SQLCA (SQLIOESTIMATE) is filled in with an estimate of the number of input/output operations required to fetch all rows of the query. Also, the sqlerrd[2] field of the SQLCA (SQLCOUNT) is filled with either the actual number of rows in the cursor (a value greater than or equal to 0), or an estimate thereof (a negative number whose absolute value is the estimate). It is the actual number of rows if the database server can compute it without counting the rows. The database can also be configured to always return the actual number of rows, but this can be expensive.
If cursor-name is specified by an identifier or string, the corresponding DECLARE CURSOR statement must appear before the OPEN in the C program; if the cursor-name is specified by a host variable, the DECLARE CURSOR statement must execute before the OPEN statement.
PermissionsMust have SELECT permission on all tables in a SELECT statement, or EXECUTE permission on the procedure in a CALL statement.
Side effectsOPEN causes the complete materialization of an INSENSITIVE cursor's result set.
If access plan caching is enabled, some SQL warnings that would be returned to the application at OPEN time may be suppressed. The suppressed warnings include warnings to indicate that the cursor type has changed, that the underlying query is not deterministic, or that string truncation has occurred with one or more literal constants embedded in the statement.
See also Standards and compatibilitySQL/2008 Use of the OPEN statement within embedded SQL is part of optional SQL language feature B031, "Basic dynamic SQL". The use of the OPEN statement within a stored procedure is a core feature of SQL/2008. The ISOLATION LEVEL and BLOCK clauses are vendor extensions, as is the ability to OPEN a cursor over a CALL statement. In the SQL/2008 standard, WITH HOLD is specified as part of the DECLARE CURSOR statement, and not on OPEN.
The setting of specific values in the SQLCA is a vendor extension.
Transact-SQL The OPEN statement is supported by Adaptive Server Enterprise. Adaptive Server Enterprise does not support the ISOLATION LEVEL, BLOCK, and WITH HOLD clauses.
ExampleThe following examples show the use of OPEN in embedded SQL.
EXEC SQL OPEN employee_cursor; |
and
EXEC SQL PREPARE emp_stat FROM 'SELECT empnum, empname FROM Employees WHERE name like ?'; EXEC SQL DECLARE employee_cursor CURSOR FOR emp_stat; EXEC SQL OPEN employee_cursor USING :pattern; |
The following example is from a procedure or trigger.
BEGIN
DECLARE cur_employee CURSOR FOR
SELECT Surname
FROM Employees;
DECLARE name CHAR(40);
OPEN cur_employee;
LP: LOOP
FETCH NEXT cur_employee INTO name;
IF SQLCODE <> 0 THEN LEAVE LP END IF;
...
END LOOP
CLOSE cur_employee;
END |
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