In this module, we will explore how to interface with databases using Control Language (CL). This is a crucial skill for automating tasks that involve data retrieval, manipulation, and storage. By the end of this module, you will be able to connect to databases, execute SQL queries, and handle the results within your CL programs.

1. Database Connectivity: Understanding how to establish a connection to a database.
2. Executing SQL Queries: Learning how to run SQL commands from within a CL program.
3. Handling Query Results: Managing the data returned from SQL queries.
4. Error Handling: Implementing error handling for database operations.

To interact with a database, you first need to establish a connection. In CL, this is typically done using the RUNSQL command, which allows you to execute SQL statements.

• Explanation:
  • RUNSQL: The command used to execute SQL statements.
  • SQL('...'): The SQL statement to be executed.
  • CONNECT TO MYDATABASE USER MYUSER USING MYPASSWORD: The SQL command to connect to a database named MYDATABASE with the user MYUSER and password MYPASSWORD.

Once connected, you can execute various SQL queries to interact with the database.

• Explanation:
  • SELECT * FROM EMPLOYEES: This SQL query retrieves all records from the EMPLOYEES table.

• Explanation:
  • INSERT INTO EMPLOYEES (ID, NAME, DEPARTMENT) VALUES (1, 'John Doe', 'HR'): This SQL query inserts a new record into the EMPLOYEES table.

Handling the results of a query involves capturing the data returned by the SQL statement and processing it within your CL program.

• Explanation:
  • DCL VAR(&RESULT) TYPE(*CHAR) LEN(100): Declares a variable &RESULT to store the query result.
  • RUNSQL SQL('SELECT NAME FROM EMPLOYEES WHERE ID = 1') OUTPUT(&RESULT): Executes the SQL query and stores the result in the &RESULT variable.

Proper error handling is essential to ensure your CL programs can gracefully handle any issues that arise during database operations.

• Explanation:
  • DCL VAR(&SQLCODE) TYPE(*DEC) LEN(15 5): Declares a variable &SQLCODE to store the SQL return code.
  • RUNSQL SQL('SELECT * FROM NON_EXISTENT_TABLE') SQLCODE(&SQLCODE): Executes the SQL query and stores the return code in &SQLCODE.
  • IF COND(&SQLCODE *NE 0) THEN(DO): Checks if the SQL return code is not zero (indicating an error).
  • SNDPGMMSG MSG('Error occurred: ' *CAT &SQLCODE): Sends a program message with the error code.

1. Objective: Write a CL program that connects to a database, retrieves employee names from the EMPLOYEES table, and handles any errors that occur.
2. Steps:
   • Connect to the database.
   • Execute a SELECT query to retrieve employee names.
   • Store the results in a variable.
   • Implement error handling to manage any issues.

• Explanation:
  • The program connects to the database and checks for connection errors.
  • It then executes a SELECT query to retrieve employee names and checks for query errors.
  • If successful, it sends a program message with the retrieved employee names.

In this module, you learned how to interface with databases using CL. You now know how to establish a connection, execute SQL queries, handle query results, and implement error handling. These skills are essential for automating tasks that involve database interactions. In the next module, we will explore how to use APIs to extend the functionality of your CL programs.