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Questions that build the mental models behind the language. No hand-holding - answer, see why, move on.

SQL

SELECT, filtering, joins, aggregation, window functions, and the NULL edge cases that catch everyone off guard.

19 topics200+ questions

Recommended order

Each topic builds on the one before. Start at step 1 and work down.

Foundation
1
SELECT Basics

where everything starts

2
Filtering

WHERE clause

3
NULL

the absent value

4
Sorting
5
Aggregation

COUNT, SUM, AVG

6
Grouping

GROUP BY

7
Filtering Groups

HAVING

Core
8
Joins

most tested concept

9
Self Joins
10
Subqueries
11
CTEs

cleaner than nested subqueries

12
Recursive CTEs

hierarchies and sequences

13
CASE Expressions
14
Set Operations

UNION, INTERSECT, EXCEPT

Advanced
15
Window Functions

hardest topic, do last

16
Date Filtering
17
Date Functions
18
String Functions
19
Distinct

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