Open folder
Launch NullReed and open your practice folder.
Workflows
sql coding practice with NullReed
03
Practice LEFT JOIN logic
You want to return rows with no match by using a LEFT JOIN with IS NULL, review the diff before accepting changes, and check the output, while considering the sql keywords every developer should know.
Create script
Use write_file to generate the seed SQL script.
Run query
Use Shell to execute the query against your database.
Check output
Read the result file and verify the NULL rows.
Example exercise file
Find employees without departments using LEFT JOIN.
- write_file
exercises.sqlcreated - edit_file
exercises.sqldiff shown - Shell
db-client < exercises.sqlexit 0 - read_file
output.txtloaded
waiting for your OK before the next stepRejectAccept
exercises.sql
-- Exercise 1: Find employees without departments
-- Task: Return names where department is missing
SELECT e.name
FROM employees e
LEFT JOIN departments d ON e.dept_id = d.id
WHERE d.id IS NULL;
-- Exercise 2: Count missing departments
SELECT COUNT(*)
FROM employees e
LEFT JOIN departments d ON e.dept_id = d.id
WHERE d.id IS NULL;This read-only file contains three standard SQL queries that demonstrate JOIN, GROUP BY, and LEFT JOIN with IS NULL filtering for non-matching rows.
sql join practice workflow
Create seed data
You start by using write_file to create a SQL script that defines your practice tables and inserts invented data, so your work remains isolated from production databases. This is sql coding practice. The agent then reads the script to verify its structure and content. You can practice sql without relying on tutorials by writing queries locally. Switch to Ask first mode so the agent pauses before actions that change something. This setting ensures you approve data-changing statements before they run. The setup program is about 34 MB and runs on Windows 10 or 11. NullReed helps you learn sql join practice by comparing your output with expected results.
Run and verify
The agent runs your database client via Shell and saves output to a text file, so you can verify correctness and compare it later. This helps. You then use read_file to view the results alongside your expected outcomes. The agent highlights any differences in the output, such as extra rows or missing columns. You can accept the changes or ask for corrections using edit_file, which shows a diff for your approval. A clear direction to learn sql when stuck is to compare your actual output against the expected results. The agent highlights any differences in the output, such as extra rows or missing columns. You can then refine your queries based on these precise observations.
