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Displaying posts with tag: sql (reset)
Workaround for MySQL’s “can’t specify target table for update in FROM clause” Error

In MySQL, you cannot do this: create table t (i int primary key, j int); insert into t values (1, 1); update t set j = (select max(j) from t) + 1; The UPDATE statement will raise an error as follows: SQL Error [1093] [HY000]: You can't specify target table 't' for update in FROM … Continue reading Workaround for MySQL’s “can’t specify target table for update in FROM clause” Error →

Newsletter Repost – OpenLampTech issue #109

WooCommerce block product editor | Escaping output in PHP and Laravel | SQL must go | GitHub and MySQL v8. OpenLampTech is a media and content source for PHP, MySQL, and the LAMP stack.

The Newsletter for PHP and MySQL Developers

Receive a copy of my ebook, “10 MySQL Tips For Everyone”, absolutely free when you subscribe to the OpenLampTech newsletter.

Thank you for reading this post. Please share it with someone else who would enjoy it as well.

Josh Otwell has a passion to grow as a PHP Developer, SQL expert, and technical blogger/writer.

Disclaimer: The majority of examples in this post, are performed in a personal development/learning …

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Index Selectivity

Introduction In this article, we are going to see how Index Selectivity works in relational database systems and why the database Optimizer might choose to avoid using an index if the number of matching records is large. Index selectivity is inversely proportional to the number of index entries matched by a given value. So, a unique index has the highest selectivity because only a single entry can be matched by any given value. On the other hand, if column values are skewed, then a column value matching a large number of table... Read More

The post Index Selectivity appeared first on Vlad Mihalcea.

SQL 1 v.s. SQL 3

In Alan Beaulieu’s wonderful book Learning SQL: Generate, Manipulate, and Retrieve Data, he uses a SQL 1 to demonstrates a CROSS JOIN in MySQL counting from 1 to 100. My students always find it difficult to read because the subqueries take so much space it makes it difficult to see the process, for example he gives this SQL 1 solution:

SELECT ones.x + tens.x + 1 AS counter
FROM
 (SELECT 0 AS x UNION ALL
  SELECT 1 AS x UNION ALL
  SELECT 2 AS x UNION ALL
  SELECT 3 AS x UNION ALL
  SELECT 4 AS x UNION ALL
  SELECT 5 AS x UNION ALL
  SELECT 6 AS x UNION ALL
  SELECT 7 AS x UNION ALL
  SELECT 8 AS x UNION ALL
  SELECT 9 AS x ) ones CROSS JOIN
 (SELECT 0 AS x UNION ALL
  SELECT 10 AS x UNION ALL
  SELECT 20 AS x UNION ALL
  SELECT 30 AS x UNION ALL
  SELECT 40 AS x UNION ALL
  SELECT 50 AS x UNION ALL
  SELECT 60 AS x UNION ALL
  SELECT 70 AS x UNION ALL
  SELECT 80 AS x UNION ALL
  SELECT 90 AS x ) tens
ORDER BY counter;

While anybody with a …

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5 Websites To Learn More SQL – Substack Repost

SQL is foundational in web and application programming. There are many websites and resources online to learn SQL. I like these 5 websites and think you will too…

The Newsletter for PHP and MySQL Developers

Receive a copy of my ebook, “10 MySQL Tips For Everyone”, absolutely free when you subscribe to the OpenLampTech newsletter.

Read the article: 5 Websites To Learn More SQL

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CodeIgniter 4 Database Features Overview in 2022 – Substack Repost

CodeIgniter 4 is a solid, well-designed PHP framework and one I enjoy using and exploring every chance I get. In 2022, the CodeIgniter 4 team released many database-related upgrades. Learn more about the ones I found most significant in this OpenLampTech report.

The Newsletter for PHP and MySQL Developers

Receive a copy of my ebook, “10 MySQL Tips For Everyone”, absolutely free when you subscribe to the OpenLampTech newsletter.

Head over to the OpenLampTech publication page and read more on this CodeIgniter 4 piece.

Want to support the OpenLampTech publication? …

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OpenLampTech issue #58 – Substack Repost

OpenLampTech is back with another solid newsletter covering the PHP, MySQL, and LAMP stack media for you. I hope you are enjoying these newsletters. I know I learn and enjoy each and every one of them in more ways than one. Be sure and share the publication with someone else you think would be interested in this content. Thank you!

OpenLampTech has top-level sponsorship opportunities in the weekly newsletter for your brand, product, or service. As a starter publication, collaboration is very budget-friendly. Learn more by inquiring here.

The Newsletter for PHP and MySQL Developers

Receive a copy of my ebook, “10 MySQL Tips For Everyone”, absolutely free when you subscribe to the OpenLampTech newsletter.

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Simulate LEAD() Window Function using correlated subquery

In my honest opinion, MS Access is one garbage of a database. More likely, database is too strong of a word. While I won’t be using Access in this article, there is a story there (but I’m not here to have an Access bash party). Continue reading for an example of how you may use a correlated subquery and simulate the LEAD() Window Function.

The Newsletter for PHP and MySQL Developers

Receive a copy of my ebook, “10 MySQL Tips For Everyone”, absolutely free when you subscribe to the OpenLampTech newsletter.

Image by  …

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OpenLampTech issue #54 – Substack Repost

We have another packed issue of OpenLampTech for you this week. And, we have our first sponsor with a smashing deal to help you configure your MySQL servers with ease. Thank you Releem for partnering with OpenLampTech this week!

The Newsletter for PHP and MySQL Developers

Receive a copy of my ebook, “10 MySQL Tips For Everyone”, absolutely free when you subscribe to the OpenLampTech newsletter.

In OpenLampTech issue #54, we have content covering:

  • SQL Wildcards
  • PHP Magic Methods Explained
  • Managing CSS in WordPress block themes
  • WordPress as a Twitter alternative?
  • And much much more

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AlmaLinux MySQL+Perl

A quick primer on Perl programs connecting to the MySQL database. It’s another set of coding examples for the AlmaLinux instance that I’m building for students. This one demonstrates basic Perl programs, connecting to MySQL, returning data sets by reference and position, dynamic queries, and input parameters to dynamic queries.

  1. Naturally, a hello.pl is a great place to start:
    #!/usr/bin/perl
    
    # Hello World program.
    print "Hello World!\n";
    

    After setting the permissions to -rwxr-xr-x. with this command:

    chmod 755 hello.pl
    

    You call it like this from the Command-Line Interface (CLI):

    ./hello.pl
    

    It prints:

    Hello World!
    
  2. Next, a connect.pl program lets us test the Perl::DBI connection to the MySQL database.
    #!/usr/bin/perl
    
    # Import libraries.
    use strict;
    use warnings;
    use v5.10;     # for …
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