A Technical I.T./DevOps Blog
Problem scenario
You are trying to integrate PHP and Postgresql on you Ubuntu/Debian Linux OS. You run this command: sudo apt-get -y install php-pgsql
You receive this error:
Reading package lists… Done
Building dependency tree
Reading state information… Done
E: Unable to locate package php-pgsql
What should you do?
Solution
#1 Find out what version of php you have.
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Continue reading “How Do You Fix the Problem “Unable to locate package php-pgsql”?”
Problem scenario
You want to integrate C++ programs with Postgresql on an Ubuntu instance of AWS. You want to use pqxx (http://pqxx.org/development/libpqxx/) as it is an API connector for C++ to Postgres. How do you use libqxx?
Solution
#1 Install Postgresql. To install Postgresql, run this as root or with a “sudo ” in front of it: apt-get install postgresql
#2 To execute SQL commands,
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Continue reading “How Do You Use the C++ Connector for Libpqxx?”
Problem scenario
You try to compile a C++ program (i.e., a .cpp file). You get this message: “fatal error: pqxx/pqxx: No such file or directory.” You want to install pqxx on your Ubuntu server in AWS. What do you do?
Solution
#1 Log into the server. Run this command as root or with a sudo in front it:
add-apt-repository ppa:jtv/ppa
#Press enter in response to the prompt from the command above.
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Continue reading “How Do You Install pqxx on an AWS Instance of Ubuntu?”
Problem scenario
To find the version of Postgres when you can enter the SQL database, you would run this SQL command with no quotes: “SELECT version();”
In this situation you cannot enter the Postgres database (and therefore can run no SQL commands). You want to know more about the installation of Postgres to troubleshoot why you cannot enter it. How do you find the version of Postgresql that is installed?
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Continue reading “How Do You Find the Version of Postgres without Running a SQL Command?”
Problem scenario
You have a PHP web page that integrates with Postgres behind the scenes. You find that when a SQL command returns nothing (e.g., when a table name is used and it is known to not exist in the underlying database), the PHP web page is blank. You want the result to be more clear about what happened or potentially happened. How do you handle an exception or commonly occurring SQL query with no results using PHP?
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Problem scenario
You want to create a table in a specific Postgres database. You want to use a command line interface (not a GUI) for this task. (The GUI version of these directions can be found here.) What are the SQL commands to do this?
Solution
This assumes you have a role (a username and password) to connect to the Postgres database with permissions to create tables.
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Continue reading “How Do You Create a Table inside a Specific Postgres Database?”
Problem scenario
You want to see the names of the tables of a specific Postgres database. You know the Postgres database name. How do you do list its tables?
Solution
This assumes you have a role (a username and password) to connect to the Postgres database.
1. Connect to the Postgres database (e.g., either through a web front-end or the command line interface).
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Continue reading “How Do You List the Tables of a Specific Postgres Database?”
Problem scenario
Using PHP you want to connect to a specific database to run SQL queries. How do you do this?
Solution
Assuming you have installed PHP and Postgres on the same Ubuntu Linux server, install the php-pgsql package. Follow this link if you need assistance.
1. Create a file like this named contint.php:
<?php
$host
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Continue reading “How Do You Connect to a Specific Database in Postgres Using PHP?”
Problem scenario
You want a web page with a text field to enter a single line of SQL code. You want this code (as opposed to some fixed, pre-written code) to execute. How do you do this?
Solution
This is more dangerous because SQL injection attacks are a serious problem. This link is how to have a PHP page execute fixed code.
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Problem scenario
You want to read in user input via a web page. You then want that user input to participate in an invocation of a SQL command. How do you get user input to be a variable in the construction of a SQL command that is automatically executed when a web-page button is clicked?
Solution
Warning
This does not prevent against SQL injection attacks.
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Continue reading “How Can You Accept User Input with PHP and Use It in a SQL Command?”