Everything you need to learn SQL. Free.

The shape of a query: choose columns, filter rows, sort, and limit what comes back.

• N001 SELECT and Column Expressions
• N002 FROM and Table References
• N003 WHERE Clause and Comparison Operators
• N004 Literal Values, Data Types, and Type Casting
• N005 NULL Semantics and IS NULL
• N006 Boolean Logic in WHERE (AND, OR, NOT)
• N007 ORDER BY and Result Sorting
• N008 LIMIT and OFFSET
• N009 Column Aliases and Expression Naming
• N010 DISTINCT
• N011 Arithmetic and Comparison Expressions
• N012 BETWEEN, IN, and LIKE

Aggregation, grouping, joins, and your first subqueries. The everyday analyst toolkit.

• N013 Aggregate Functions (COUNT, SUM, AVG, MIN, MAX)
• N014 GROUP BY
• N015 HAVING
• N016 CASE WHEN Expressions
• N017 INNER JOIN
• N018 LEFT JOIN and RIGHT JOIN
• N019 FULL OUTER JOIN
• N020 CROSS JOIN
• N021 Self-Joins
• N022 Joining Multiple Tables
• N023 UNION, UNION ALL, INTERSECT, EXCEPT
• N024 Scalar Subqueries
• N025 Subqueries in WHERE (IN, EXISTS, ANY, ALL)
• N026 Derived Tables (Subqueries in FROM)
• N027 Conditional Aggregation (CASE inside Aggregates)

CTEs, date and string work, conditional logic, and an introduction to window functions.

• N028 COALESCE and NULLIF
• N029 NULL Handling in Joins and Aggregates
• N030 Common Table Expressions (CTEs)
• N031 Chained CTEs
• N032 Date and Time Types in PostgreSQL
• N033 Date Truncation and Extraction
• N034 Date Arithmetic and Intervals
• N035 String Functions (LENGTH, UPPER, LOWER, TRIM, SUBSTRING)
• N036 String Concatenation and Formatting
• N037 Pattern Matching (LIKE, ILIKE, SIMILAR TO, Regex)
• N038 Window Functions Introduction (OVER, PARTITION BY)
• N039 ROW_NUMBER, RANK, DENSE_RANK
• N040 Aggregate Window Functions (SUM, AVG, COUNT OVER)
• N041 Temp Tables and CREATE TABLE AS SELECT

The full window-function range, lateral joins, JSON, and recursive queries.

• N042 LAG and LEAD
• N043 FIRST_VALUE, LAST_VALUE, NTH_VALUE
• N044 Window Frames (ROWS, RANGE, GROUPS)
• N045 NTILE and Percentile Functions
• N046 DISTINCT ON
• N047 Correlated Subqueries
• N048 LATERAL Joins
• N049 FILTER Clause on Aggregates
• N050 STRING_AGG and ARRAY_AGG
• N051 generate_series() for Sequences and Date Spines
• N052 Recursive CTEs
• N053 JSONB Field Extraction
• N054 JSONB Aggregation (jsonb_agg, json_build_object)
• N055 Date Spine Construction and Zero-Fill Patterns
• N056 Period-over-Period Analysis
• N057 Grouping by Date Periods

Analytical patterns and query reasoning: running totals, sessionization, reading EXPLAIN.

• N058 Multi-CTE Query Architecture
• N059 Join Fanout and Aggregate Correctness
• N060 Reading EXPLAIN Output
• N061 Query Structure Patterns for Performance
• N062 Choosing Between Subqueries, CTEs, and Joins
• N063 NULL Propagation in Complex Queries
• N064 Running Totals and Cumulative Metrics
• N065 Sessionization and Funnel Analysis Patterns
• N066 Analyst Debugging Patterns