SQL Common Table Expressions Explained !!!

Common Table Expressions: A Game Changer for Intermediate SQL Queries

Common Table Expressions, or CTEs, are a powerful tool for creating more transparent and understandable SQL queries. A CTE allows you to define a subquery once and reference it multiple times within your main query, which is incredibly useful for complex financial transformations.

When using CTEs, especially in finance projects, you can perform reconciliations at various levels of aggregation, join data, and conduct comparative analyses more efficiently. Here’s a quick breakdown of the syntax for writing a CTE:

WITH: This clause signals the start of a CTE.
table_name AS: This part names your CTE.
(SELECT a, b, c FROM table1): This is your query, enclosed in parentheses.
Once defined, a CTE behaves like any other table in subsequent SQL queries within the same session, simplifying your SQL scripts significantly.

Example with Two CTEs:

sql
Copy code
WITH
q1 AS (SELECT * FROM Table1),
q2 AS (SELECT * FROM Table2)
FROM q1
In the above script, two CTEs are defined and then joined in a main SQL query. It showcases how seamlessly CTEs can integrate into larger data operations, acting just like regular tables.

Watch the video below for a real-world example and detailed explanation of how to effectively use CTEs to streamline your SQL scripts.

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