LEFT JOIN Filters Step by Step

A compact LEFT JOIN filter book for readers who need exact finite ON-match versus post-join WHERE behavior: left/right inputs, right-side matches, repeated left rows, NULL padding, WHERE after the join, padded rows dropped by right-side filters, right-value filters, and guarded expected facts.

LEFT JOIN Filters

Left and Right Tables
ON Finds Right Matches
One Left Row Can Repeat
Unmatched Left Gets NULL Padding
WHERE Runs After the Join
WHERE Drops Padded Rows
Right Value Filter After Join
Honest by Construction