codeigniter select for update

In CodeIgniter, the "select for update" statement is used to lock selected rows for update within a transaction. The following steps explain how to use "select for update" in CodeIgniter:

1. Start a database transaction using the $this->db->trans_start() method. This begins a transaction which allows for multiple operations to be performed as a single unit of work.

2. Use the select() method to specify the columns to be retrieved from the table. For example: $this->db->select('column1, column2').

3. Add the from() method to specify the table from which to retrieve the data. For example: $this->db->from('tablename').

4. Include the where() method to specify the conditions for selecting the rows. For example: $this->db->where('condition').

5. Call the get_for_update() method to retrieve the selected rows and lock them for update. For example: $query = $this->db->get_for_update();

6. Perform the necessary operations on the selected data within the transaction.

7. Complete the transaction using the $this->db->trans_complete() method. This commits the changes if all operations within the transaction were successful, or rolls back the transaction if any operation failed.

Following these steps allows for the proper use of "select for update" in CodeIgniter, ensuring that selected rows are locked for update within a transaction.