create table person (id int, last_name varchar(30), first_name varchar(30)) create unique clustered index person_id on person (id) create index person_name on person (last_name, first_name) 在上例中,id上创建了聚集索引,下面
其中有 聚集索引clustered index(id), 非聚集索引index(username)。 使用以下语句进行查询,不需要进行二次查询,直接就可以从非聚集索引的节点里面就可以获取到查询列的数据。 select id, username from t1 where username = '小明' select username from t1 where username = '小明' 1. 但是使用以下语句进行查询,...
不过在本项目中，这些问题并未带来额外挑战，因为本次迁移是从对默认值支持较为有限的 Sybase ASE 向默认值支持更为广泛的 PostgreSQL 进行的。索引迁移总体而言，索引的迁移也是较为简单直接的过程，但在两种数据库支持的索引类型上存在一些差异值得关注：Sybase ASE 支持聚簇索引（CLUSTERED INDEX），而 PostgreSQL 不...
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在PostgreSQL中,可以使用JSONB数据类型来存储和操作JSON数据。如果需要在PostgreSQL中拆分JSON列,可以使用JSONB函数和操作符来实现。 拆分JSON列的步骤如下: 1...
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--First we create the index CREATE INDEX member_name_idx ON member USING btree (upper(last_name), upper(first_name)); ALTER TABLE member CLUSTER ON member_name_idx; Once a clustered index is created to force a recluster, you simply do this ...
首先重命名你的表，并包括键或索引（此外，不要在PostgreSQL索引中给予PK前缀，因为PostgreSQL创建了开箱即...
I think the current estimate formula for VACUUM is > pretty reasonable. Consider a table T with N rows and P pages clustered > on serial key k. Assume reltuples is initially correct. If the starting condition involves uniform tuple density throughout the table, with matching reltuples/relpa...
In our May 2008 issue of Postgres OnLine Journal, wecross compared Microsoft SQL Server 2005, MySQL 5, and PostgreSQL 8.3. Some people mentioned well since 8.4 has now come out, shouldn't we go back and update the reference. We deliberated and decided not to. To be ...