Tutorial Chapter 4: Query by Example

Parent topic: Tutorial Chapter 4: Query by Example

Retrieving data from the Database

When an SQL SELECT statement in your application will retrieve more than one row, a cursor must be used to pass the selected data to the program one row at a time.

Using Cursors
The cursor is a data structure that represents a specific location within the active set of rows that the SELECT statement retrieved.
The SQLCA.SQLCODE
The SQLCA name stands for "SQL Communication Area". The SQLCA variable is a predefined record containing information on the execution of an SQL statement.
Example custquery.4gl (function cust_select)
This function is called by the function query_cust, if the row count returned by the function get_cust_cnt indicates that the criteria previously entered by the user and stored in the variable where_clause would produce an SQL SELECT result set.
Example: custquery.4gl (function fetch_cust)
This function is designed so that it can be reused each time a row is to be fetched from the customer database table; a variable is passed to indicate whether the cursor should move forward one row or backward one row.
Example: custquery.4gl (function fetch_rel_cust)
This function is called by the MENU options next and previous in the custmain.4gl module.
Example: custquery.4gl (function display_cust)
This function displays the contents of the mr_custrec record in the form. It is called by the functions query_cust and fetch_rel_cust.

Parent topic: Tutorial Chapter 4: Query by Example