In this query, you use the `time_bucket` function provided by TimescaleDB to map individual readings into one-hour intervals or "buckets." Then, the AVG function calculates the average temperature for each inte
AVG functionThe AVG function determines the average of all selected values of a column.Syntax:AVG (* | [DISTINCT] ALL | column_name) ParametersNameDescription column_name Name of the column * The asterisk(*) indicates all the rows. DISTINCT This clause is optional. It indicates uniqueness...
create [or replace ]function 函数名 [(参数名[in]数据类型...)] return 数据类型 {is|as} [说明部分] BEGIN 语句序列 return (表达式) [EXCEPTION 例外处理程序] END 函数名;/ 编写一个函数,计算几个人的平均工资,并在函数体的循环过程中输出结果 create or replace function average_sal(v_n in number...
“老师好:这有一个新问题,关于谁修改了work_mem, maintenance_work_mem,那些用户在自己的权限下,可以直接修改本地session的参数,这也可以导致PostgreSQL崩溃,那这个问题我们怎么发现和排查,比如一个用户将maintenance_work_mem 改成6G或更大,我们怎么发现这些用户修改过这些参数呢,因为SESSION 失效后参数设置也失效了,...
2024-11-28 21:19:08.222 EST [1931] LOG: checkpoint complete: wrote 3 buffers (0.0%); 0 WAL file(s) added, 0 removed, 0 recycled; write=0.001 s, sync=0.002 s, total=0.005 s; sync files=2, longest=0.001 s, average=0.001 s; distance=0 kB, estimate=0 kB; lsn=0/4F879F8, red...
SELECTcalculate_average_salary(); 这将返回employees表中所有员工的平均工资。 存储过程还可以接受输入参数,以便根据不同的条件执行不同的操作。下面是一个示例的存储过程,用于根据部门 ID 获取员工数量: CREATEORREPLACEFUNCTIONcount_employees_by_department(department_idINT)RETURNSINTAS$$DECLAREemployee_countINT;BEGI...
To calculate the average price of books in each genre, the following SQL query is used: avg_price_by_genre.sql SELECT genre, AVG(price) AS avg_price FROM books GROUP BY genre; This query uses theGROUP BYclause to group the results by thegenrecolumn. TheAVGfunction calculates the average...
An aggregate function produced a single result for an entire group or table. Aggregate functions are used to produce summarized results. They operate on sets of rows. They return results based on groups of rows. By default, all rows in a table are treated as one group. The GROUP BY clause...
PG中的查询执行部分含有三个核心模块:Portal,Executor与ProcessUtility。其中Portal是查询执行过程中创建的核心数据,包含执行的策略信息等。PG将查询策略分为两大类,一类是数据查询操作,实现了对数据表数据的增删查改,该类功能实现的入口函数为Executor();另一类是功能操作,类似于DDL,比如游标,表的模式创建以及事务相关...
在数据库集群中,有3个配置文件,分别是:postgresql.conf,pg_hba.conf和pg_ident.conf。其中postgresql.conf为服务器主要的配置文件,pg_hba.conf是客户端认证配置文件,pg_ident.conf用来配置哪些操作系统用户可以映射为数据库用户。 连接与认证 参考文章: