1
我有这个查询来获取给定过滤器的行数,由于db太大而需要很长时间才能得到结果,有没有什么办法可以优化它我使用PostgreSQL 8.2优化在PostgreSql中为多个分组按字段选择行数
SELECT COUNT(1) as numrows from (select lower(column1) as column1, column2, column3, column4, sum(column5) as column5, sum(column6) as column6
from table_name tablename
where column_date >= 'SOME DATE' and column_date < 'SOME DATE'
group by lower(column1) as column1, column2, column3, column4 ORDER BY column5 desc) allRows
这里是我得到EXPLAIN查询
XN Aggregate (cost=849751.05..849751.05 rows=1 width=0)
-> XN Subquery Scan allrows (cost=805802.05..842426.22 rows=2929933 width=0)
-> XN HashAggregate (cost=805802.05..813126.89 rows=2929933 width=26)
-> XN Seq Scan on table_name tablename (cost=0.00..512808.79 rows=29299326 width=26)
Filter: ((column_date < 'SOME DATE'::date) AND (column_date >= 'SOME DATE'::date))
显示我们从EXPLAIN分析输出。 – zero323
另外(1),sum()调用和“order by”的原因是什么? (2)你为什么使用大约两年前达到报废时间的版本? http://www.postgresql.org/support/versioning/ –