SQL Lesson 10: INSERT, UPDATE and DELETE Safely
Change data without disasters: INSERT rows, UPDATE with a WHERE you have tested, DELETE carefully, transactions with BEGIN/ROLLBACK/COMMIT, and habits that prevent “I updated…
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Query data like a pro — explained for Excel users.
SQL Lesson 9: Working With Dates
SQL Lesson 9: Working With Dates
Filter and group by dates in SQL: ISO date format, month and year ranges, strftime/date functions in SQLite (and SQL Server/PostgreSQL equivalents), adding days,…
Read article →SQL Lesson 8: CASE — If-Then in SQL
SQL Lesson 8: CASE — If-Then in SQL
Use CASE to label rows (price bands, order sizes), count conditions side by side with SUM(CASE…), handle NULLs with readable labels, and build pivot-style…
Read article →SQL Lesson 7: Subqueries
SQL Lesson 7: Subqueries
Use a query inside a query: compare with an average, filter with IN and NOT IN, find the row with the maximum, query a…
Read article →SQL Lesson 6: JOINs — Combining Tables
SQL Lesson 6: JOINs — Combining Tables
Combine tables with JOIN: primary and foreign keys, INNER JOIN, table aliases, joining three tables, LEFT JOIN to find missing matches, and the duplicate-row…
Read article →SQL Lesson 5: GROUP BY and HAVING
SQL Lesson 5: GROUP BY and HAVING
Get totals per group with GROUP BY — customers per region, orders per status, sales per month — filter groups with HAVING, and know…
Read article →SQL Lesson 4: COUNT, SUM, AVG, MIN and MAX
SQL Lesson 4: COUNT, SUM, AVG, MIN and MAX
Summarise data with aggregate functions: COUNT(*) vs COUNT(column), SUM, AVG with ROUND, MIN and MAX on numbers and dates, filtering before aggregating, and how…
Read article →SQL Lesson 3: ORDER BY and LIMIT
SQL Lesson 3: ORDER BY and LIMIT
Sort SQL results with ORDER BY, ascending and descending, by several columns and by calculated values; get top-N lists with LIMIT, and understand why…
Read article →SQL Lesson 2: WHERE — Filtering Rows
SQL Lesson 2: WHERE — Filtering Rows
Filter rows in SQL with WHERE: comparison operators, AND/OR with brackets, IN, BETWEEN, LIKE with % and _, and IS NULL — the SQL…
Read article →SQL Lesson 1: SELECT — Reading Data
SQL Lesson 1: SELECT — Reading Data
Your first SQL queries: what tables, rows and columns are, install DB Browser for SQLite, SELECT columns, SELECT *, calculated columns with AS, DISTINCT…
Read article →SQL from Zero: A Complete Beginner’s Guide (with Practice)
SQL from Zero: A Complete Beginner’s Guide (with Practice)
Learn SQL from the very beginning: tables, SELECT, WHERE, ORDER BY, aggregates, GROUP BY, JOINs, NULLs, subqueries, CTEs, window functions and changing data —…
Read article →SQL for Excel Users: 10 Queries That Replace Everyday Excel Work
SQL for Excel Users: 10 Queries That Replace Everyday Excel Work
Learn SQL through tasks you already do in Excel — filters, sorting, pivot tables, VLOOKUP and remove duplicates — with 10 queries you can…
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