30个实用SQL语句，玩转PostgreSQL

作者 |慕枫Java
来源 | 慕枫技术笔记(ID：lulideguang)

引言

PostgreSQL是一款功能非常强大的开源关系型数据库，它支持哈希索引、反向索引、部分索引、Expression 索引、GiST、GIN等多种索引模式，同时可安装功能丰富的扩展包。相较于Mysql，PostgreSQ支持通过PostGIS扩展支持地理空间数据、支持嵌套循环，哈希连接，排序合并三种表连接方式等一系列的强化功能。本文主要整理总结了30个实用SQL，方便大家可以高效利用PostgreSQL。

实用SQL语句

一、数据库连接

1、获取数据库实例连接数

select count(*) from pg_stat_activity;

2、获取数据库最大连接数

show max_connections

3、查询当前连接数详细信息

select * from pg_stat_activity;

4、查询数据库中各个用户名对应的数据库连接数

select usename, count(*) from pg_stat_activity group by usename;

二、赋权操作

1、为指定用户赋予指定表的select权限

GRANT SELECT ON table_name TO username;

2、修改数据库表所属的ownner

alter table table_name owner to username;

3、授予指定用户指定表的所有权限

grant all privileges on table product to username;

4、授予指定用户所有表的所有权限

GRANT ALL PRIVILEGES ON ALL TABLES IN SCHEMA public TO username;

三、数据库表或者索引

1、获取数据库表中的索引

select * from pg_indexes where tablename = 'product';

2、获取当前db中所有表信息

select * from pg_tables;

3、查询数据库安装了哪些扩展

select * from pg_extension;

4、查询数据库中的所有表及其描述

select relname as TABLE_NAME ,col_description(c.oid, 0) as COMMENTS from pg_class c where relkind = 'r' and relname not like 'pg_%' and relname not like 'sql_%'

四、获取数据大小

1、查询执行数据库大小

select pg_size_pretty (pg_database_size('db_product'));

2、查询数据库实例当中各个数据库大小

select datname, pg_size_pretty (pg_database_size(datname)) AS size from pg_database;

3、查询单表数据大小

select pg_size_pretty(pg_relation_size('product')) as size;

4、查询数据库表包括索引的大小

select pg_size_pretty(pg_total_relation_size('table_name')) as size;

5、查看表中索引大小

select pg_size_pretty(pg_indexes_size('product'));

6、获取各个表中的数据记录数

select relname as TABLE_NAME, reltuples as rowCounts from pg_class where relkind = 'r' order by rowCounts desc

7、查看数据库表对应的数据文件

select pg_relation_filepath('product');

五、数据库分析

1、查看数据库实例的版本

select version();

2、查看最新加载配置的时间

select pg_conf_load_time();

3、查看当前wal的buffer中有多少字节未写入磁盘

select pg_xlog_location_diff(pg_current_xlog_insert_location(),pg_current_xlog_location());

4、查询最耗时的5个sql

select * from pg_stat_statements order by total_time desc limit 5;

备注：需要开启pg_stat_statements

5、获取执行时间最慢的3条SQL，并给出CPU占用比例

SELECT substring(query, 1, 1000) AS short_query,
round(total_time::numeric, 2) AS total_time,
calls,
round((100 * total_time / sum(total_time::numeric) OVER ())::numeric, 2) AS percentage_cpu
FROM pg_stat_statements
ORDER BY total_time DESC
LIMIT 3;

6、分析评估SQL执行情况

EXPLAIN ANALYZE SELECT * FROM product

7、查看当前长时间执行却不结束的SQL

select datname, usename, client_addr, application_name, state, backend_start, xact_start, xact_stay, query_start, query_stay, replace(query, chr(10), ' ') as query from (select pgsa.datname as datname, pgsa.usename as usename, pgsa.client_addr client_addr, pgsa.application_name as application_name, pgsa.state as state, pgsa.backend_start as backend_start, pgsa.xact_start as xact_start, extract(epoch from (now() - pgsa.xact_start)) as xact_stay, pgsa.query_start as query_start, extract(epoch from (now() - pgsa.query_start)) as query_stay , pgsa.query as query from pg_stat_activity as pgsa where pgsa.state != 'idle' and pgsa.state != 'idle in transaction' and pgsa.state != 'idle in transaction (aborted)') idleconnections order by query_stay desc limit 5;

8、查出使用表扫描最多的表

select * from pg_stat_user_tables where n_live_tup > 100000 and seq_scan > 0 order by seq_tup_read desc limit 10;

9、查询读取buffer最多的5个SQL

select * from pg_stat_statements order by shared_blks_hit+shared_blks_read desc limit 5;

10、获取数据库当前的回滚事务数以及死锁数

select datname,xact_rollback,deadlocks from pg_stat_database

11、查询访问指定表的慢查询

select * from pg_stat_activity where query ilike '%<table_name>%' and query_start - now() > interval '10 seconds';

六、数据库备份(非SQL)

1、备份postgres库并tar打包

pg_dump -h 127.0.0.1 -p 5432 -U postgres -f postgres.sql.tar -Ft

2、备份postgres库，转储数据为带列名的INSERT命令

pg_dumpall -d postgres -U postgres -f postgres.sql --column-inserts

总结

本文主要针对PostgreSQL数据库中在日常开发中比较常用的SQL进行了分类的总结，那么大家日常开发工作中，可以在分析数据库性能、数据库连接情况、sql执行情况等数据库分析方面都有对应的SQL语句来进行支撑。