https://sql-simplified.pages.dev Learn SQL from absolute beginner to advanced with interactive, in-browser SQL examples in every lesson. en What SQL is, why it matters, and how you'll learn it in this course. https://sql-simplified.pages.dev/learn/introduction https://sql-simplified.pages.dev/learn/introduction How to choose exactly which columns you want back from a table using SELECT. https://sql-simplified.pages.dev/learn/select https://sql-simplified.pages.dev/learn/select Use the WHERE clause and comparison operators to filter which rows a query returns. https://sql-simplified.pages.dev/learn/where https://sql-simplified.pages.dev/learn/where Use DISTINCT to see the unique values in a column, without repeats. https://sql-simplified.pages.dev/learn/distinct https://sql-simplified.pages.dev/learn/distinct Control the order of your query results with ORDER BY, ascending or descending, across one or more columns. https://sql-simplified.pages.dev/learn/order-by https://sql-simplified.pages.dev/learn/order-by Use LIMIT to cap how many rows a query returns, and OFFSET to skip ahead in the results. https://sql-simplified.pages.dev/learn/limit https://sql-simplified.pages.dev/learn/limit Use AS to give columns and tables friendlier, more readable names in your query results. https://sql-simplified.pages.dev/learn/aliases https://sql-simplified.pages.dev/learn/aliases Perform calculations directly in your queries using +, -, *, and / to create computed columns. https://sql-simplified.pages.dev/learn/arithmetic https://sql-simplified.pages.dev/learn/arithmetic What NULL means in SQL, how it differs from zero or an empty string, and how to test for it correctly. https://sql-simplified.pages.dev/learn/null https://sql-simplified.pages.dev/learn/null Search for partial text matches using the LIKE operator and its % and _ wildcards. https://sql-simplified.pages.dev/learn/like https://sql-simplified.pages.dev/learn/like Use the IN operator to cleanly match a column against a list of possible values. https://sql-simplified.pages.dev/learn/in https://sql-simplified.pages.dev/learn/in Use the BETWEEN operator to filter values that fall within an inclusive range of numbers or dates. https://sql-simplified.pages.dev/learn/between https://sql-simplified.pages.dev/learn/between Collapse rows into groups so you can summarize data with aggregate functions like COUNT, SUM, and AVG. https://sql-simplified.pages.dev/learn/group-by https://sql-simplified.pages.dev/learn/group-by Filter groups after aggregation — the GROUP BY equivalent of WHERE. https://sql-simplified.pages.dev/learn/having https://sql-simplified.pages.dev/learn/having Combine rows from two tables where a related key matches on both sides. https://sql-simplified.pages.dev/learn/inner-join https://sql-simplified.pages.dev/learn/inner-join Keep every row from the left table, matching rows from the right table when available — filling gaps with NULL. https://sql-simplified.pages.dev/learn/left-join https://sql-simplified.pages.dev/learn/left-join Keep every row from the right table and match rows from the left when available. https://sql-simplified.pages.dev/learn/right-join https://sql-simplified.pages.dev/learn/right-join Keep every row from both tables, matching where possible and filling NULLs on either side. https://sql-simplified.pages.dev/learn/full-join https://sql-simplified.pages.dev/learn/full-join Stack the results of two or more queries with matching columns into a single result set. https://sql-simplified.pages.dev/learn/union https://sql-simplified.pages.dev/learn/union Add if/else logic directly inside a query to label, bucket, and transform values on the fly. https://sql-simplified.pages.dev/learn/case https://sql-simplified.pages.dev/learn/case Summarize many rows into a single number with COUNT, SUM, AVG, MIN, and MAX. https://sql-simplified.pages.dev/learn/aggregate-functions https://sql-simplified.pages.dev/learn/aggregate-functions Nest one query inside another to compute values you can use in WHERE, FROM, or SELECT. https://sql-simplified.pages.dev/learn/subqueries https://sql-simplified.pages.dev/learn/subqueries Name a query with WITH so you can reference it like a temporary table and write cleaner SQL. https://sql-simplified.pages.dev/learn/cte https://sql-simplified.pages.dev/learn/cte Use WITH RECURSIVE to walk hierarchies and sequences like org charts and numbered lists. https://sql-simplified.pages.dev/learn/recursive-cte https://sql-simplified.pages.dev/learn/recursive-cte Compute running totals, ranks, and per-group comparisons without collapsing rows like GROUP BY does. https://sql-simplified.pages.dev/learn/window-functions https://sql-simplified.pages.dev/learn/window-functions Speed up lookups with database indexes — what they are, when to add them, and their trade-offs. https://sql-simplified.pages.dev/learn/indexes https://sql-simplified.pages.dev/learn/indexes Write queries the planner can execute efficiently — read less data, use indexes, and avoid surprises. https://sql-simplified.pages.dev/learn/query-optimization https://sql-simplified.pages.dev/learn/query-optimization Group multiple statements into an all-or-nothing unit with BEGIN, COMMIT, and ROLLBACK. https://sql-simplified.pages.dev/learn/transactions https://sql-simplified.pages.dev/learn/transactions Save a query as a named, reusable virtual table with CREATE VIEW. https://sql-simplified.pages.dev/learn/views https://sql-simplified.pages.dev/learn/views Package reusable SQL logic on the server with parameters, branching, and transactions. https://sql-simplified.pages.dev/learn/stored-procedures https://sql-simplified.pages.dev/learn/stored-procedures Automatically run SQL in response to INSERT, UPDATE, or DELETE events on a table. https://sql-simplified.pages.dev/learn/triggers https://sql-simplified.pages.dev/learn/triggers Test whether a subquery returns any rows — a fast, set-based way to filter. https://sql-simplified.pages.dev/learn/exists https://sql-simplified.pages.dev/learn/exists Add new rows to a table with INSERT INTO — single rows, multiple rows, and from a query. https://sql-simplified.pages.dev/learn/insert https://sql-simplified.pages.dev/learn/insert Modify existing rows in a table with UPDATE — change one column or many, for one row or millions. https://sql-simplified.pages.dev/learn/update https://sql-simplified.pages.dev/learn/update Remove rows from a table with DELETE — scoped by WHERE, or wipe a table entirely. https://sql-simplified.pages.dev/learn/delete https://sql-simplified.pages.dev/learn/delete Transform and inspect text with UPPER, LOWER, LENGTH, CONCAT, SUBSTRING, and more. https://sql-simplified.pages.dev/learn/string-functions https://sql-simplified.pages.dev/learn/string-functions Work with dates using EXTRACT, DATE_TRUNC, intervals, and date arithmetic. https://sql-simplified.pages.dev/learn/date-functions https://sql-simplified.pages.dev/learn/date-functions Join a table to itself to compare rows within the same table, like employees and their managers. https://sql-simplified.pages.dev/learn/self-joins https://sql-simplified.pages.dev/learn/self-joins Produce every combination of rows from two tables with CROSS JOIN. https://sql-simplified.pages.dev/learn/cross-joins https://sql-simplified.pages.dev/learn/cross-joins Compare result sets: keep rows in one but not another (EXCEPT), or only the shared rows (INTERSECT). https://sql-simplified.pages.dev/learn/except-intersect https://sql-simplified.pages.dev/learn/except-intersect Summarize student grades per course using AVG, MAX, MIN, and COUNT alongside a join for readable course names. https://sql-simplified.pages.dev/examples/aggregate-functions https://sql-simplified.pages.dev/examples/aggregate-functions Use CASE WHEN to bucket employees into salary bands, and inside COUNT() to conditionally tally rows. https://sql-simplified.pages.dev/examples/case-expression https://sql-simplified.pages.dev/examples/case-expression Use a WITH clause to compute total spend per customer as a named, reusable result set, then filter and join against it. https://sql-simplified.pages.dev/examples/cte https://sql-simplified.pages.dev/examples/cte Find movies whose budget exceeds the average budget for their own genre, using a subquery that references the outer query's current row. https://sql-simplified.pages.dev/examples/correlated-subqueries https://sql-simplified.pages.dev/examples/correlated-subqueries Use EXISTS with a correlated subquery to find authors who have published at least one book, and NOT EXISTS for the opposite. https://sql-simplified.pages.dev/examples/exists-operator https://sql-simplified.pages.dev/examples/exists-operator Collapse individual orders into one summary row per customer using GROUP BY, COUNT, and SUM. https://sql-simplified.pages.dev/examples/group-by-basics https://sql-simplified.pages.dev/examples/group-by-basics Use INNER JOIN to attach department names to employee records, keeping only rows that match on both sides. https://sql-simplified.pages.dev/examples/inner-join https://sql-simplified.pages.dev/examples/inner-join Use LEFT JOIN to list every movie alongside its audience rating, including movies that have never been rated. https://sql-simplified.pages.dev/examples/left-join https://sql-simplified.pages.dev/examples/left-join Rank employees by salary within their own department using RANK() OVER (PARTITION BY ...), without collapsing rows the way GROUP BY does. https://sql-simplified.pages.dev/examples/window-functions https://sql-simplified.pages.dev/examples/window-functions