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INNER JOIN and LEFT JOIN (The Two You Need First) — Ravi Sir's Cards

All SQL cards

Revision cards

What INNER JOIN really keeps. INNER JOIN is the easiest join to write, but it quietly drops rows that have no match.
What INNER JOIN really keeps · PNG

Interview cards

Why did my total double after a join? The key repeats on the other side, so each row was repeated once per match. The SUM then counted the same fee more than once.
Why did my total double after a join? · PNG

Comparison cards

INNER JOIN vs LEFT JOIN. INNER JOIN keeps only matching pairs. LEFT JOIN keeps every row of the table after FROM and adds the matches.
INNER JOIN vs LEFT JOIN · PNG