PostgreSQL DBA (12)-Application of statistics in calculating the selection rate # 2
This section briefly introduces the application of statistical information (frequency MCV and histogram HISTOGRAM) in PG database to calculate the selection rate of multi-conditional query in the form of examples.
First, calculate the selection rate
The test data generation script is detailed in the previous section and will not be repeated here.
SQL scripts and execution plans:
< 2312 and c1 >500 QUERY PLAN-Seq Scan on public.t_int (cost=0.00..2040.00 rows=18375 width=9) Output: C1 C2 Filter: (t_int.c1
< 2312) AND (t_int.c1 >500) (3 rows)
The SQL statement has two constraints: C1
< 2312 和 c1 >PG is actually the selection rate of ">" to "500" = "C1 < 2312" selection rate-"C1"
