SQL for Data Science

SQL Essentials

SQL is essential for database querying.

Basic Queries

SELECT columns FROM table WHERE conditions GROUP BY column HAVING aggregate_conditions.

ORDER BY column (ASC/DESC), LIMIT n. DISTINCT for unique values.

Joins

INNER JOIN: matching rows from both. LEFT JOIN: all from left, matching right.

RIGHT JOIN, FULL OUTER JOIN. Multiple joins: (table1 JOIN table2 ON ...) JOIN table3.

Aggregations

COUNT, SUM, AVG, MIN, MAX. GROUP BY creates groups. HAVING filters groups.

Window functions: ROW_NUMBER(), RANK(), SUM() OVER (PARTITION BY).

Key Takeaways

1. SELECT-FROM-WHERE is core query structure
2. JOINs combine tables
3. Window functions enable complex analytics