Anti-join
Finding rows with no match in another table, usually a LEFT JOIN followed by WHERE ... IS NULL.
An ordinary (inner) join keeps only rows that match on both sides. A
LEFT JOINkeeps every row of the left table, filling the right side's columns with NULL where nothing matches. That makes it the tool for questions about absence: which products haven't sold, which customers never ordered. The pattern, called an anti-join, is a left join followed byWHERE right_side.key IS NULL.
Try it now
SQL is written SELECT first but worked out in this order, which is why a WHERE can't use a column alias but ORDER BY can.
Learn it properly
SQL for analysis · Subqueries, CASE, common table expressions, outer joins and window functions on real order data. About 45 minutes.
Other terms from the same lesson
- common table expression: A named step in a SQL query, written with WITH, that later steps can use like a table.
- subquery: A query inside another query, which runs first and hands its result to the outer one.
- window function: A SQL calculation across a set of rows, like a rank or a running total, that keeps every row instead of grouping them.
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