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Recursive Queries Using Common Table Expressions

Common Table Expressions (CTEs) are a bit complex and difficult to understand at first blush. Many of the tutorials and examples on the net don't make it any easier for those just starting out. I thought I'd put together a quick gist that tries to simplify the concept and demonstrate how to do recursive queries using CTEs.

Keep in mind that CTEs have other uses besides just recursive queries but this gist is just about how they can be used to create recursive searches.

I'm using SQLite in this example but any SQL language that implements the WITH keyword should be able to do the same thing. If you've never used SQLite before, you are missing out on an amazing, open source, stand alone, SQL engine. I encourage you to check it out.

A practical example

Zabrane

-module(parse_xlsx).

-export([
    parse_file/1,
    fetch_worksheet/1
    ]).

parse_file(File) ->
    case fetch_worksheet(File) of
        {ok, #{ worksheet := notfound }} ->

Zabrane

//!\file csv.c \brief fast csv parser

//MIT copyright (c) 2016 kelas <me@kel.as>

#include "___.h"
#include "csv.h"

Z FILE* infile;
Z FILE* outfile;
Z ID last_id = 0;

Zabrane

#!/bin/bash
#
# Enable nopasswd mode for sudo on macOS from the userspace in fast and totally non-interactive way
#
# Type the password last time to apply the new mode and forget it for any console task for ages
# Use the rollback to restore password protection
#
# Developed and tested by https://juliyvchirkov.github.io/ under the MIT license on macOS Big Sur 11.2.0
#
# Get latest version at https://gist.github.com/juliyvchirkov/3ca76582ed6b6a8366c9e7d60644960d

Zabrane

%% @author atill
%%
%% @doc
%% CSV parsing module.  Parsed CSV will be processed and converted
%% into a list containing the separated values, lines are separated
%% by the newline atom.

-module(csv).

-import(lists, [reverse/1]).

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#!/usr/bin/env escript

-record(ecsv,{
state = field_start, %%field_start|normal|quoted|post_quoted
cols = undefined, %%how many fields per record
current_field = [],
current_record = [],
fold_state,
fold_fun %%user supplied fold function
}).

Zabrane

#!/bin/bash

set -o errexit
set -o errtrace
set -o functrace
set -o pipefail
set -o nounset

[ -z ${DEBUG+x} ] || set -o xtrace

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Googlebot/2.1 (+http://www.google.com/bot.html)  # Pattern: Googlebot\/ / URL: http://www.google.com/bot.html
Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)  # Pattern: Googlebot\/ / URL: http://www.google.com/bot.html
Mozilla/5.0 (iPhone; CPU iPhone OS 6_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/6.0 Mobile/10A5376e Safari/8536.25 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)  # Pattern: Googlebot\/ / URL: http://www.google.com/bot.html
Mozilla/5.0 (iPhone; CPU iPhone OS 8_3 like Mac OS X) AppleWebKit/537.36 (KHTML, like Gecko) Version/8.0 Mobile/12F70 Safari/600.1.4 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)  # Pattern: Googlebot\/ / URL: http://www.google.com/bot.html
Mozilla/5.0 (iPhone; CPU iPhone OS 8_3 like Mac OS X) AppleWebKit/600.1.4 (KHTML, like Gecko) Version/8.0 Mobile/12F70 Safari/600.1.4 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)  # Pattern: Googlebot\/ / URL: http://www.google.com/bot.html
Mozilla

Zabrane

<IfModule log_config_module>
    # Define monitor environment variable for logs exclusion
    SetEnvIf User-Agent "^F5\ BIG-IP\ Monitor$" monitor=yes

    # Define forwarded environment variable for logs management
    SetEnvIf X-Forwarded-For "^.*\..*\..*\..*" forwarded=yes

    #
    # The following directives define some format nicknames for use with
    # a CustomLog directive (see below).

Zabrane

[Unit]
Description=hitch
After=syslog.target network.target


[Service]
Type=forking
#Restart=on-failure
LimitNOFILE=131072
Environment="HITCH_OPTIONS=--config /etc/hitch/hitch.conf"