Inspect a query plan

EXPLAIN SELECT * FROM users WHERE id = 5;
EXPLAIN (ANALYZE, FORMAT JSON) SELECT * FROM orders WHERE user_id = 5;
EXPLAIN ANALYZE SELECT u.name, count(*) FROM users u JOIN orders o ON o.user_id = u.id GROUP BY
  u.name;

Output shapes (implemented in crates/executor/src/query/explain.rs)#

• Seq Scan on T (cost=1.01..1.01 rows=N width=W) [(filter: WHERE)]
• Joins: Seq Scan on A JOIN B; UNION → Append [ALL]; INTERSECT → Hash Intersect [ALL]; EXCEPT → Hash Except [ALL]; WITH → CTE Scan (N CTEs); writes: Insert|Update|Delete on T.
• EXPLAIN ANALYZE executes the inner statement and appends Actual Rows: N, Execution Time: 0.00ms.
• FORMAT JSON returns one JSON doc with Plan{Node Type, Relation, Startup/Total Cost, Plan Rows/Width} plus actuals when analyze.

What to look for#

• Relation + filter: is the predicate where you expect?
• Actual Rows vs estimated rows: large gaps mean the shape assumption is off.
• v0.1.0 has no cost-based planner (crates/optimizer is a stub) — EXPLAIN describes scan/join/set shapes, not an index-choice trace. Measure with EXPLAIN ANALYZE and Performance.

Constraints#

EXPLAIN accepts (ANALYZE, FORMAT json|text, COSTS|BUFFERS|…) options; unknown options are tolerated in the option list but only analyze/format change output.