Software engineering facts, information, and skills categorized as PostgreSQL
Regex and iregex are the two field lookups that enable us to search database with regular expressions. regex is case-sensitive where as iregexis case-insensitive.
isnullIn django, the NULL valuein the database field is tested with field lookup isnull It takes either True or False, which correspond to SQL queries of IS NULL and IS NOT NULL, respectively.
Field lookups are how we specify the conditions in the WHERE clause of an SQL. They are specified as keyword arguments for QuerySet methodslike filter(), exclude() and get().
Field lookups are how we specify the conditions in the WHERE clause of an SQL. They are specified as keyword arguments for QuerySet methodslikefilter(), exclude() and get().
Heroku comes with nice database backup tools, both commandline and web based. But how to export results of an SQL query?
Very often, you will have the requirement to concatenate two columns in a table, on the fly in SELECT SQL. For example, first name and last name needed to be combined at username. The + operator is available in MicroSoft's database servers, but it is not part of PostgreSQL or SQL standard. PostgreSQL very well support string concatenation in SQL results. Let us assume that we have a table like
PostgreSQL could be configured to limit number of simultaneous connections to the database. The heroku comes with plans having connection limits. The 'Hopby' plans comes with 20 connections where as standard plans comes startings with 120 conection. When we start developing and testing, especially automated testings, the hobby plans raise error PG::Error (FATAL: too many connections for role "xxxxxxx"). If we check the connections with heroku cli, we get
Python
Python is an interpreted(processed at runtime by the interpreter), object-oriented(supports Object-Oriented style), interactive, simple, easy to learn, portable, extensible, embeddable, high-level programming language for general-purpose programming. Created by Guido van Rossum at the National Research Institute for Mathematics and Computer Science in the Netherlands and first released in 1991. Python is derived from ABC, Modula-3, SmallTalk, Algol-68, C, C++, Unix shell and other scripting languages.Python's source code is avaliable under the GNU General Public License (GPL) which guarantees end users the freedom to run, study, share and modify the software.
To create a database, create a user and grant privileges to the user on command line is often a requirement only when a new project is initialized. The process is described in few simple steps. The local system has a super user named 'postgres' in the Linux, who can login to local database without password. The operating System - Linux - does have the user postgres, but the password is unknown. The solution is to login to the system as a user with super user privileges. Then use sudo and su commands to login as postgresql