The four groups
Letters of ACID, expanded
ATOMICITY · CONSISTENCY · ISOLATION · DURABILITY
SQL DML verbs
INSERT · UPDATE · DELETE · MERGE
SQL transaction isolation levels
READ COMMITTED · READ UNCOMMITTED · REPEATABLE READ · SERIALIZABLE
Words that follow ROLL
BACK · BAR · OVER · CALL
Why this puzzle works
Database-engineering deep cut. ISOLATION in yellow is the trap — the ACID 'I' *is* isolation, which is also the subject of the entire blue group. Don't put 'isolation' with the levels. BACK is purple (rollback) but a beginner might want to file it with 'undo verbs' (which don't exist as a group in this puzzle). Difficulty-4: blue's four isolation levels are textbook DB-systems content, easy to mis-order vs ACID semantics.
How to read a Connectle without solving it
A code-themed grouping puzzle rewards counting as much as recognition. Start by listing every plausible group, then notice which tiles appear in two lists. Whichever group has exactly four unambiguous members is your anchor — solve it first and the rest of the board collapses by elimination. The hardest tier (purple) is almost always wordplay: tiles that share a prefix or suffix, not a concept. If a tile feels orphaned, ask whether the same word could follow or precede a common engineering word like root, stack, cache, or queue.