1、序列
以自增serial類型主鍵的序列：
alter sequence s_seq restart with 1; #重置序列
select currval('tablename_pid_seq');
select nextval('tablename_pid_seq');
select setval('tablename_pid_seq',1);
2、修改表
--刪除約束
alter table tablename alter column col drop not null;
--添加約束
alter table tablename add constraint tablename_col_uq unique(col);
--修改類型/長度
alter table tablename alter column col type character varying(2000);
--添加列
alter table tablename add column col character varying(255);
--刪除列
alter table tablename drop column col;
3、查看數據使用空間
select pg_size_pretty(pg_database_size('dbname'));
4、優化與監控
#查看數據庫
select * from pg_stat_database
#查看鏈接情況
select * from pg_stat_activity where datname = 't0pagped'
select count(1) from pg_stat_activity;
#根據IP地址匯總連接數
select client_addr,count(client_addr) as num from pg_stat_activity
where datname = 't0pagped' and application_name = 'PostgreSQL JDBC Driver'
group by client_addr
order by num desc
#最大連接數
show max_connections;
#查看表使用情況
select * from pg_stat_user_tables where relname = 'kg_askbob_entity_ins_capital' order by seq_scan desc
#查看表索引
select * from pg_stat_user_indexes where relname = 'kg_askbob_entity_ins_capital'
PostgreSQL統計信息：
https://yq.aliyun.com/articles/697692