SQL Data Retrieval with CTEs and Subqueries

Query Using Subqueries and Common Table Expressions (CTEs)

-- Common Table Expression (CTE) to retrieve data from Table A
WITH CTE_A AS (
    SELECT column_1, column_2
    FROM Table_A
    WHERE condition = 'specific_condition'
),

-- Subquery to get aggregated data from Table B
Subquery_B AS (
    SELECT parent_column, COUNT(child_column) AS child_count
    FROM Table_B
    GROUP BY parent_column
),

-- Main query combining CTE and Subquery results
Main_Query AS (
    SELECT A.column_1, A.column_2, B.parent_column, B.child_count
    FROM CTE_A A
    JOIN Subquery_B B ON A.column_1 = B.parent_column
)

-- Final select to retrieve data from the Main_Query
SELECT *
FROM Main_Query;

Annotations:

1. CTE_A:

   • Used to retrieve specific data from Table A based on a condition.

2. Subquery_B:

   • Calculates the count of child records for each parent record in Table B.

3. Main_Query:

   • Joins the results of CTE_A and Subquery_B to combine data from different sources.
   • Helps in organizing and simplifying the final data retrieval.

4. Final Select:

   • Retrieves the final results from the Main_Query for presenting to the user.

By using a combination of CTEs and subqueries effectively, this query retrieves data from multiple related tables in a complex database schema, showcasing how different SQL features can be utilized to handle such scenarios.