How can we see a histogram of movies on IMDB with a particular rating? Or how much movies grossed at the box office each month? Or how many movies there are of each genre? These are examples of data aggregation questions, and this lesson will teach u…

https://coderwall.com/p/whf3-a/hierarchical-data-in-postgres ------------------------------------------------------------------------------- This tip will try to answer the following questions: How can we represent a tree of data in postgres How can…

使用 PGO 在 Kubernetes 上运行 Cloud Native PostgreSQL:来自 Crunchy Data 的 Postgres Operator! Cloud Native PostgreSQL https://www.crunchydata.com/products/crunchy-postgresql-for-kubernetes/ Crunchy Data https://www.crunchydata.com/ Postgres Operator https://g…

聚合运算之group 语法: db.collection.group( { key:{key1:1,key2:1}, cond:{}, reduce: function(curr,result) { }, initial:{}, finalize:function() { } } ) key: 分组字段 cond:查询条件 reduce:聚合函数 initial:初始化 finalize:统计一组后的回调函数 #查询每个栏目下的商品数量 db.goods.group( { key:{cat_id…

group 语法   db.collection.group({ key:{field:1},//按什么字段进行分组 initial:{count:0},//进行分组前变量初始化,该处声明的变量可以在以下回调函数中作为result的属性使用 cond:{},//类似mysql中的having,分组后的查询返回 reduce: function ( curr, result ) { }, //The function takes two arguments: the current documen…

1. 通常,你可能有一个计算的属性依赖于数组中的所有元素来确定它的值.例如,你可能想要计算controller中所有todo items的数量,以此来确定完成了多少任务. export default Ember.Controller.extend({ todos: [ Ember.Object.create({ isDone: true }), Ember.Object.create({ idDone: false }), Ember.Object.create({ isDone: true…

Delete example: DELETE FROM movies ; Update example: UPDATE movies ;…

由于接触了华为的elk大数据平台,里面封装的是postgres ,就想着安装一下,熟悉一下postgres数据. 安装包下载:https://www.postgresql.org/ftp/source/ 可以选择自己想下载的版本.这里我们下载v10.5 随后开始安装: 1.把包上传到虚拟机中postgresql-10.5.tar.gz 2.解压缩: gunzip postgresql-10.5.tar.gz tar -xvf postgresql-10.5.tar 3.进行编辑安装: ./con…

master节点安装元数据库,采用postgres:#useradd postgres#password postgressu - postgreswget https://ftp.postgresql.org/pub/source/v10beta2/postgresql-10beta2.tar.gztar zxvf postgresql-10beta2.tar.gzcd postgresql-10beta2 ./configuremakesumake install mkdir /usr/lo…

This document describes the installation of PostgreSQL using the source    code distribution. (If you are installing a pre-packaged distribution,    such as an RPM or Debian package, ignore this document and read the    packager's instructions instea…