方法2:使用pg_class和pg_index系统表 PostgreSQL 还提供了一些系统表,如pg_class和pg_index,这些表可以用来查询更底层的元数据信息。 SELECT a.attname AS column_name FROM pg_index i JOIN pg_attribute a ON a.attnum=ANY(i.indkey) JOIN pg_class t ON t.oid=i.indrelid JOIN pg_namespace n ON...
select current_database(),b.typname,count(*) from pg_attribute a,pg_type b where a.atttypid=b.oid and a.attrelid in (select oid from pg_class where relnamespace not in (select oid from pg_namespace where nspname ~ $$^pg_$$ or nspname=$$information_schema$$)) group by 1,2 ...
索引: 查看索引:select * from pg_indexes where tablename='tabename'; 删除索引:DROP INDEX indexname; 创建btree索引:CREATE INDEX indexname ON tablename USING btree(columnname); ===>唯一键索引:create unique index ... 创建hash索引:CREATE INDEX indexname ON tablename USING hash(columnname); 查...
CREATETABLEcustomer(name)ASSELECT'cust'||iFROMgenerate_series(1,1000)ASg(i);CREATEINDEXi_customer_nameONcustomer(name);/*看一下直接对B-Tree索引列做fitler的plan*/EXPLAINSELECT*FROMcustomerWHEREname='cust999';QUERYPLAN---Index Only Scan using i_customer_name on customer...Index Cond:(name='c...
default_text_search_config,pg_catalog.english,Sets default text search configuration. default_transaction_deferrable,off,Sets the default deferrable status of new transactions. default_transaction_isolation,read committed,Sets the transaction isolation level of each new transaction. ...
Postgres循环检索SQL pgsql 循环 嵌套循环联结使用一次访问运算所得到的结果集中的每一行来与另一个表进行碰撞。如果结果集的大小是有限的并且在用来联结的列上建有索引的话,这种联结的效率通常是最高的。嵌套循环联结的运算成本主要是读取外层表中的每一行并将其与锁匹配的内层表中的行联结所需的成本。
:alpha_status, percentage_complete double precision NOT NULL DEFAULT 0.00, failure text COLLATE pg_catalog."default", CONSTRAINT pk_alpha PRIMARY KEY (alpha_id) ) CREATE INDEX super_index ON public.alpha USING btree (alpha_id COLLATE pg_catalog."default", alpha_status) ...
pg_type as t WHERE c.relname = 't_batch_task' and a.atttypid = t.oid and a.attrelid = c.oid and a.attnum>0; 索引管理 创建索引 drop index if exists t_user_username; create index t_user_username on t_user (username);
“Sequential Scan on TBL1”和“TIndex Scan on TBL2”分别对应对TBL1和TBL2的table access method。表1将顺序地从对应页面获取元组,表2通过索引访问元组。 在介绍pg扫描方法之前,有以下几个概念: HEAP:用于存放表中整行数据。每个表可能对应多个文件,文件被分割为很多页,每个页面默认8k. 在页面内部,通过item...
Adam Hendelgave a brief history ofpgmq, is a “lightweight message queue like AWS SQS and RSMQ, but on Postgres.” Gülçin Yıldırım Jelínekintroducedpgzx, “a library for developing PostgreSQL extensions written inZig.”