HOWTO

HOWTO : Query json data in SQLite

A self note for querying json data in SQLite. BTW, I think SQLite is an under utilized and under appreciated swiss army tool for data storage and manipulation. And thanks to Richard Hipp, it is free.

If you have a column defined as a json type in your SQLite database, quickest way to search for the data is json_extract. A full set of functions available are documented at https://www.sqlite.org/json1.html

If you have a column named family_details in a table family with the following json in it as an example 

{
	"father": {
		"name": "dad",
		"birthday": "1/1/2000",
		"pet_name": "daddy"
	},
	"mother": {
		"name": "mom",
		"birthday": "1/1/2001",
		"pet_name": "mommy"
	},
	"sons": [
		{
			"name": "son_one",
			"birthday": "1/2/2020",
			"pet_name": "sonny_one"
		},
		{
			"name": "son_two",
			"birthday": "1/2/2021",
			"pet_name": "sonny_two"
		}
	],
	"daughters": [
		{
			"name": "princess_one",
			"birthday": "1/2/2020",
			"pet_name": "princy_one"
		},
		{
			"name": "princess_two",
			"birthday": "1/2/2021",
			"pet_name": "princy_two"
		}
	]
}

and you want to print the name of the father, you can use

select json_extract(family_details, '$.father.name') as father_name
from family

json_extract uses the name of the column and the json node as parameters. In this case, we used $(which denotes the root), father and name (under father) as the json node.

April 13, 2021 by Databases HOWTO Technology 0

HOW TO : Add commas (,) at the end of every line using Notepad++

Thanks for this great nugget from Sumama Waheed

Many a time, you get some data as a CSV file and need to copy some of that data and include it in a SQL statement. For instance one of the rows in the CSV was first name in the format below

employee_id
1234
8765
9808
1235
8734
6723

And you need to put it in a SQL statement as below

SELECT * FROM employee_table
WHERE employee_table.employee_id IN (1234,
8765,
9808,
1235,
8734,
6723)

That’s a lot of adding commas (,) at the end of every line. You can do it quickly in Notepad++ (you can do the same in any editor that supports regex) using the regex capability in search and replace using ($) as the search string and $, as the replace string.

May 12, 2020 by HOWTO Technology Windows 0

HOW TO : Configure nginx to use URI for modifying response content

That was a pretty long title for the post :). I love nginx for it’s flexibility and ease of use. It is like a swiss army knife.. can do a lot of things :).

We needed to serve some dynamic content for one of our use cases. If user visits a site using the following URL format http://example.com/23456789/678543 , we want to respond with some html content that is customized using the 23456789 and 678543 strings.

A picture might help here

Here’s how this was achieved

  • Define a location section in the nginx config to respond to the URL path specified and direct it to substitute content 
    location ~ "^/(?<param1>[0-9]{8})/(?<param2>[0-9]{6})" {

            root /var/www/html/test/;
            index template.html;
            sub_filter_once off;
            sub_filter '_first_param_' '$param1';
            sub_filter '_second_param_' '$param2';
            rewrite ^.*$ /template.html break;
    }

create a file named template.html with the following content in /var/www/html/test

Breaking down the config one line at a time

location ~ "^/(?<param1>[0-9]{8})/(?<param2>[0-9]{6})" : The regex is essentially matching for the first set of digits after the / and adding that as the value for variable $param1. The first match is a series of 8 digits with each digit in the range 0-9. The second match is for a series of 6 digits with each digit in the range 0-9 and it will be added as the value for variable $param2

root /var/www/html/test/; : Specifying the root location for the location.

index template.html; : Specifying the home page for the location.

sub_filter_once off; : Specify to the sub_filter module to not stop after the first match for replacing response content. By default it processes the first match and stops.

sub_filter 'first_param' '$param1'; : Direct the sub_filter module to replace any text matching first_param in the response html with value in variable $param1.

sub_filter 'second_param' '$param2'; : Direct the sub_filter module to replace any text matching second_param in the response html with value in variable $param1.

rewrite ^.*$ /template.html break; : Specify nginx to server template.html regardless of the URI specified.

Big thanks to Igor for help with the configs!!

May 7, 2020 by HOWTO Technology Web 1

HOW TO : Set $GOPATH

Been dabbling in go recently and I was surprised that the default install doesn’t setup the $GOPATH environment variable.

If you are running it on a Linux box, here is how your can set the $GOPATH variable

Add the following lines to ~/.bashrc file 

export GOPATH=$HOME/go
export PATH=$PATH:$GOROOT/bin:$GOPATH/bin

October 28, 2018 by HOWTO Programming 0