Gunakan kasus 3 - Panggilan fungsi dalam pernyataan SELECT

Memanggil fungsi dalam where klausa dapat mengurangi kinerja kueri saat fungsi tersebut VOLATILE dan Anda tidak menggunakan select kata kunci saat memanggil fungsi:

Select * from tab_name where FieldName = FunctionName(parameters);

Pemindaian indeks berjalan jika select pernyataan digunakan saat memanggil fungsi:

Select * from tab_name where FieldName = ( select FunctionName(parameters) );

pnr_numberBidang memiliki indeks dalam rnr_expiry_date tabel. Indeks digunakan saat membandingkan nilai dalam where klausa.

explain analyze select * from perf_user.rnr_expiry_date where pnr_number= 'EE9F41';

"Index Scan using rnr_expiry_date_idx3 on rnr_expiry_date  (cost=0.29..8.31 rows=1 width=72) (actual time=0.020..0.021 rows=1 loops=1)"
"  Index Cond: ((pnr_number)::text = 'EE9F41'::text)"
"Planning Time: 0.063 ms"
"Execution Time: 0.038 ms"

Pemindaian sekuensial dilakukan ketika fungsi dipanggil tanpa select kata kunci bahkan ketika indeks tersedia di lapangan.

explain analyze select * from perf_user.rnr_expiry_date where pnr_number= perf_user.return_data();

"Seq Scan on rnr_expiry_date  (cost=0.00..27084.00 rows=1 width=72) (actual time=0.112..135.917 rows=1 loops=1)"
"  Filter: ((pnr_number)::text = (perf_user.return_data())::text)"
"  Rows Removed by Filter: 99999"
"Planning Time: 0.053 ms"
"Execution Time: 136.803 ms"

Pemindaian indeks dilakukan ketika fungsi dipanggil dengan select kata kunci.

explain analyze select * from perf_user.rnr_expiry_date where pnr_number= (select perf_user.return_data() );

"Index Scan using rnr_expiry_date_idx3 on rnr_expiry_date  (cost=0.55..8.57 rows=1 width=72) (actual time=0.058..0.061 rows=1 loops=1)"
"  Index Cond: ((pnr_number)::text = ($0)::text)"
"  InitPlan 1 (returns $0)"
"    ->  Result  (cost=0.00..0.26 rows=1 width=32) (actual time=0.021..0.022 rows=1 loops=1)"
"Planning Time: 0.147 ms"
"Execution Time: 0.111 ms"