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Displaying posts with tag: sql (reset)
MySQL Column Aliases using the AS keyword

Be it running reports or displaying data in some other visualization, SQL SELECT column expressions should be meaningful and understandable. To provide those valuable query results, SQL Developers, use a multitude of available functions, adjacent columns, or other means not readily apparent to end-users. All that being said, the column names often suffer the most as far as readability is concerned, taking on long function call names or other combined expressions. But, as luck would be on our side, there is an easy fix and that is aliasing columns using the AS keyword. Although AS is optional – in this particular context – I err on the side of readability and use it when aliasing SELECT column expressions.

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MySQL Count Weekday occurrences

Each SQL dialect is different in some way, shape, form, or fashion from the next flavor. Some dialects have this function, while others have that function. In this post, I cover porting over Oracle SQL to MySQL in order to count the number of occurrences of a specific weekday found in the current given month (at the time of writing) purely as a learning exercise focused on MySQL DATE functions and the WITH clause…

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MySQL COUNT() aggregate function – Medium cross post

I recently published a blog post over on Medium about the differences in 2 versions of the MySQL COUNT() aggregate function: COUNT(*) and COUNT(column_name or expression). I wanted to share the post here with any readers who may be interested so continue reading for more on this post…

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MySQL Aggregate Query using CodeIgniter’s Query Builder

CodeIgniter’s Query Builder ORM has class methods for nearly any kind of database access/operation you can think of. In this post, I’ll cover some of the available methods for retrieving aggregate-level query results. The examples in this post map out Query Builder method chaining to produce results you would get from a raw MySQL query. Continue reading to see more…

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MySQL Transaction Scope

The idea of ACID transactions are a basic feature of SQL’s individual Data Manipulation Language (DML) commands, like the INSERT, UPDATE, and DELETE statements. Transactions across two or more tables are a natural extension of ACID compliance features provided by DML commands. However, they require a structured programming approach, like a store procedure or like API implemented in an imperative language.

Surprisingly, transaction management wasn’t covered well in Alan Beaulieu’s Learning SQL because he only provided pseudo code logic. While I thought troubleshoot some broken MySQL SQL/PSM logic would be a good learning experience for students, it wasn’t. So, I wrote this sample code to show how to achieve an all or nothing transaction across four tables.

The code for this example on transaction management lets you perform the important tasks necessary to effect transaction …

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MySQL Query Profiling Using Performance Schema

Introduction In this article, I’m going to explain how to do query profiling using the MySQL Performance Schema. The Performance Schema has been available since MySQL 5.5.3 and allows MySQL to instrument SQL queries and store their trace information in various tables that you can later inspect in order to determine why a given SQL statement is slow. On older versions of MySQL, you might have used the SHOW PROFILE command, but since this feature has been deprecated, you should now use the Performance Schema for SQL query profiling. Enabling the MySQL... Read More

The post MySQL Query Profiling Using Performance Schema appeared first on Vlad Mihalcea.

MySQL’s AUTO_INCREMENT attribute

Most developers use some form of auto-incrementing integer counter for a given database table, ensuring uniqueness among the rows. Several of the popular SQL dialects implement this facility. For instance, MySQL’s AUTO_INCREMENT attribute is used to provide a unique identity for a table row. What exactly is the behavior of AUTO_INCREMENT? Can you explicitly use a value of your choosing for it if you need to? How does it count? Continue reading and know the answers to these questions and more…

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Import CSV file with MySQL Workbench

CSV imports with MySQL Workbench, is super simple. Since CSV’s are probably the most common data interchange format, it goes without saying that importing CSV data into MySQL is a staple task for all DBA’s and Developers. Continue reading to learn how easy it is using MySQL Workbench…

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MySQL Join Tutorial

Some believe the most important part of SQL is the ability to query data. Queries typically retrieve data by joining many tables together into useful result sets. This tutorial takes the position that visibility into the data helps those new to SQL understand how joins work. To that end, the queries use Common Tabular Expressions (CTEs) instead of tables.

Default behavior of a JOIN without a qualifying descriptor is not simple because it may return:

  • A CROSS JOIN (or Cartesian Product) when there is no ON or USING subclause, or
  • An INNER JOIN when you use an ON or USING subclause.

The following query uses JOIN without a qualifier or an ON or USING subclause. It also uses two copies of the single CTE, which is more or less a derived table and the result of a subquery held in memory. This demonstrates the key …

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MySQL Membership

MySQL membership conditions are in the MySQL 8 Documentation. They’re found in the 13.2.11.3 Subqueries with ANY, IN, or SOME section. The IN and =ANY operators both perform equality matches with one twist. The IN operator works with a set of values or a subquery but the =ANY operator only works with a subquery.

I created the digits, letters, and words tables for this example. They hold the following values respectively:

  • The numbers table holds the values of 1, 2, 3, and 4
  • The letters table holds the values of 'a', 'b', 'c', and 'd'
  • The words table holds the values of 'Captain America', 'Iron …
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