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how to exclude null values in array_agg like in string_agg using postgres?
...
SQL Fiddle
select
id,
(select array_agg(a) from unnest(canonical_users) a where a is not null) canonical_users,
(select array_agg(a) from unnest(non_canonical_users) a where a is not null) non_canonical_users
from (
SELE...
SSH免密码登陆教程 - 环境配置 - 清泛IT社区，为创新赋能！
...目标机；
要达到的目的：
A机器ssh登录B机器无需输入密码；
加密方式选 rsa|dsa均可以，默认dsa
做法：
1、登录A机器
2、ssh-keygen -t [rsa|dsa]，将会生成密钥文件和私钥文件 id_rsa,id_rsa.pub或id_dsa,id_dsa.pub
3、将 .pub 文件复制...
MySql安装配置 - 爬虫/数据库 - 清泛IT社区，为创新赋能！
1.下载服务器端，解压
2.安装Mysql服务：
进入bin目录，mysqld.exe --install (指定安装的MySql服务名)。
（卸载 net stop servicename;
mysqld.exe --remove servicename）
3.进入MySql命令模式：
mysql.exe（...
Warning: mysql_connect(): [2002] No such file or directory (trying to connect via unix:///tmp/mysql.
I'm trying to connect to my MySQL DB with the Terminal on my Apple (With PHP).
17 Answers
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Sequelize Unknown column '*.createdAt' in 'field list'
... do not contain a timestamp column.
When you do user.find it will just do SELECT user.*, which only takes the columns you actually have. But when you join, each column of the joined table will be aliased, which creates the following query:
SELECT `users`.*, `userDetails`.`userId` AS `userDetails.u...
How to achieve function overloading in C?
...neric gets the overall type of the expression and then "switches" on it to select the end result expression in the list for its type:
_Generic(1, float: 2.0,
char *: "2",
int: 2,
default: get_two_object());
The above expression evaluates to 2 - the type of the ...
From inside of a Docker container, how do I connect to the localhost of the machine?
So I have a Nginx running inside a docker container, I have a mysql running on localhost, I want to connect to the MySql from within my Nginx. The MySql is running on localhost and not exposing a port to the outside world, so its bound on localhost, not bound on the ip address of the machine.
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chown: invalid user: mysql:mysql - 更多技术 - 清泛网 - 专注C/C++及内核技术
chown: invalid user: mysql:mysqlLinux安装Mysql并赋相关目录mysql用户权限时，报错：[root]# chown -R mysql:mysql .chown: invalid user: mysql:mysql解决方法：#...Linux安装Mysql并赋相关目录mysql用户权限时，报错：
[root]# chown -R mysql:mysql .
chown: invalid user...
What columns generally make good indexes?
...earching the results speedily from tables. So it is most important step to select which columns to be indexed. There are two major places where we can consider indexing: columns referenced in the WHERE clause and columns used in JOIN clauses. In short, such columns should be indexed against which yo...
搭建高可用mongodb集群（一）——配置mongodb - 大数据 & AI - 清泛网 - 专...
...东西，所以把自己实战的步骤记录下来以备忘。我们看看如何一步一步搭建这个东东。
一、mongodb单实例。这种配置只适合简易开发时使用，生产使用不行，因为单节点挂掉整个数据业务全挂，如下图。
虽然不能生产使用，...