SQL Essentials
From SELECT to window functions — queries on demand.
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Peek inside — 3 of 218 cards
Rows in A with no match in B?
LEFT JOIN B … WHERE B.id IS NULL
Filter groups, not rows?
HAVING — WHERE runs before GROUP BY
Second-highest salary?
ORDER BY salary DESC LIMIT 1 OFFSET 1 (or DENSE_RANK)
About this deck
SQL drilled the way interviews test it: a data question on the front, the query pattern on the back. Joins taught as pictures, GROUP BY as 'one row per…', and the WHERE/HAVING split settled once and for all.
Works for any dialect — differences are flagged where they bite (LIMIT vs TOP, || vs CONCAT).
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