SQL OPEN

What is the SQL OPEN statement?

OPENS a previously declared database cursor so that rows can be fetched from the result set it represents.

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Compatible dialects for SQL OPEN: PostgreSQL, SQL Server (T-SQL), Oracle, MySQL (within procedures), IBM Db2, SQLite (limited emulation through extensions)

SQL OPEN Full Explanation

The SQL OPEN statement activates a cursor that has already been declared but not yet populated. When a cursor is opened, the database engine executes the underlying query, materializes or prepares the result set, and positions the cursor before the first row. Subsequent FETCH calls can then retrieve rows sequentially. OPEN is part of the cursor‐control trio OPEN, FETCH, CLOSE and is required in procedural SQL blocks, stored procedures, and scripts when you need row-by-row processing. Some dialects (PostgreSQL, SQL Server, Oracle) allow parameterized cursors, so OPEN can include a USING or parameter list that supplies runtime values. Attempting to OPEN an already open cursor raises an error, as does OPENing a cursor outside its declared scope. OPEN does not itself return data; it simply prepares the cursor. Always CLOSE the cursor after use to free resources.

SQL OPEN Syntax

-- Basic form
OPEN cursor_name;

-- PostgreSQL parameterized cursor
OPEN cursor_name (param1, param2);

-- Oracle USING clause
OPEN cursor_name FOR SELECT_statement;

-- T-SQL
OPEN cursor_name;

SQL OPEN Parameters

cursor_name (identifier) - Required. Name of the previously DECLAREd cursor.
parameters (expression) - Optional in some dialects. Values passed to a parameterized cursor declaration or USING clause.

Example Queries Using SQL OPEN

-- PostgreSQL example
BEGIN;
DECLARE active_users CURSOR FOR
  SELECT id, email FROM users WHERE active = true;
OPEN active_users;
FETCH NEXT FROM active_users;
CLOSE active_users;
COMMIT;

-- SQL Server example
declare employee_cur cursor for
  select EmpID, LastName from Employees where IsActive = 1;
open employee_cur;
fetch next from employee_cur;
close employee_cur;
DEALLOCATE employee_cur;

-- Oracle example with parameters
declare
  cursor sales_cur(p_region varchar2) is
    select * from sales where region = p_region;
begin
  open sales_cur('WEST');
  fetch sales_cur into ...;
  close sales_cur;
end;

Expected Output Using SQL OPEN

The cursor is placed in the OPEN state and the result set is ready
No rows are returned until FETCH is called
If the cursor is already open or undefined, the database raises an error

Use Cases with SQL OPEN

Iterating over query results inside stored procedures
Performing row-by-row complex logic that cannot be expressed in set-based SQL
Driving batch updates, calculations, or data exports
Feeding results to client applications that expect cursor APIs

Common Mistakes with SQL OPEN

Forgetting to CLOSE the cursor, leading to resource leaks
Trying to OPEN a cursor that was never DECLAREd or is out of scope
Attempting to OPEN an already open cursor
Misordering statements (FETCH before OPEN)
Supplying the wrong number of parameters for a parameterized cursor

First Introduced In

SQL-92 (cursor operations)

Frequently Asked Questions

Does OPEN return any rows?

No. OPEN only prepares the result set. Use FETCH to retrieve rows.

Can I OPEN the same cursor twice?

Not without closing it first. OPENing an already open cursor raises an error.

Is OPEN supported in MySQL?

Yes, but only inside stored procedures where cursors are allowed.

Do I always need to CLOSE after OPEN?

Yes. Always CLOSE (or DEALLOCATE in SQL Server) to release memory and locks.