面临奇怪的行为EXISTS（也适用于NOT EXISTS）生成不同的执行计划
WHERE EXISTS(...)
EXPLAIN ANALYZE
SELECT * FROM books
WHERE EXISTS (SELECT 1 FROM authors WHERE id = books.author_id AND name LIKE 'asd%');
| QUERY PLAN |
| -------------------------------------------------------------------------------------------------------------- |
| Hash Join (cost=218.01..454.43 rows=56 width=40) (actual time=0.975..0.975 rows=0 loops=1) |
| Hash Cond: (books.author_id = authors.id) |
| -> Seq Scan on books (cost=0.00..206.80 rows=11280 width=40) (actual time=0.010..0.010 rows=1 loops=1) |
| -> Hash (cost=217.35..217.35 rows=53 width=4) (actual time=0.943..0.943 rows=0 loops=1) |
| Buckets: …