मेरी निम्नलिखित तालिका और सूचकांक परिभाषाएँ हैं:
CREATE TABLE munkalap (
munkalap_id serial PRIMARY KEY,
...
);
CREATE TABLE munkalap_lepes (
munkalap_lepes_id serial PRIMARY KEY,
munkalap_id integer REFERENCES munkalap (munkalap_id),
...
);
CREATE INDEX idx_munkalap_lepes_munkalap_id ON munkalap_lepes (munkalap_id);निम्नलिखित क्वेरी में munkalap_id पर कोई भी अनुक्रमणिका क्यों नहीं है?
EXPLAIN ANALYZE SELECT ml.* FROM munkalap m JOIN munkalap_lepes ml USING (munkalap_id);
QUERY PLAN
Hash Join (cost=119.17..2050.88 rows=38046 width=214) (actual time=0.824..18.011 rows=38046 loops=1)
Hash Cond: (ml.munkalap_id = m.munkalap_id)
-> Seq Scan on munkalap_lepes ml (cost=0.00..1313.46 rows=38046 width=214) (actual time=0.005..4.574 rows=38046 loops=1)
-> Hash (cost=78.52..78.52 rows=3252 width=4) (actual time=0.810..0.810 rows=3253 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 115kB
-> Seq Scan on munkalap m (cost=0.00..78.52 rows=3252 width=4) (actual time=0.003..0.398 rows=3253 loops=1)
Total runtime: 19.786 msयदि मैं कोई फ़िल्टर जोड़ता हूं तो भी यह समान है:
EXPLAIN ANALYZE SELECT ml.* FROM munkalap m JOIN munkalap_lepes ml USING (munkalap_id) WHERE NOT lezarva;
QUERY PLAN
Hash Join (cost=79.60..1545.79 rows=1006 width=214) (actual time=0.616..10.824 rows=964 loops=1)
Hash Cond: (ml.munkalap_id = m.munkalap_id)
-> Seq Scan on munkalap_lepes ml (cost=0.00..1313.46 rows=38046 width=214) (actual time=0.007..5.061 rows=38046 loops=1)
-> Hash (cost=78.52..78.52 rows=86 width=4) (actual time=0.587..0.587 rows=87 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 4kB
-> Seq Scan on munkalap m (cost=0.00..78.52 rows=86 width=4) (actual time=0.014..0.560 rows=87 loops=1)
Filter: (NOT lezarva)
Total runtime: 10.911 ms