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Search Results for: columns

Generated (Virtual) Columns in MySQL 5.7 (labs)

About 2 weeks ago Oracle published the MySQL 5.7.7-labs-json version which includes a very interesting feature called “Generated columns” (also know as Virtual or Computed columns). MariaDB has a similar feature as well: Virtual (Computed) Columns. The …

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More then 1000 columns – get transactional with TokuDB

Recently I encountered a specific situation in which a customer was forced to stay with the MyISAM engine due to a legacy application using tables with over 1000 columns. Unfortunately InnoDB has a limit at …

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TIMESTAMP Columns, Amazon RDS 5.6, and You

This comes from an issue that I worked on recently, wherein a customer reported that their application was working fine under stock MySQL 5.6 but producing erroneous results when they tried running it on Amazon …

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Looking out for max values in integer-based columns in MySQL

Yay! My first blog post! As long as at least 1 person finds it useful, I’ve done my job. 😉 Recently, one of my long-term clients was noticing that while their INSERTs were succeeding, a …

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Big trouble with zero-length character columns in TokuDB

What good is a zero-length character column in a MySQL table? A zero-length character column has type of ‘char(0)’. If it is nullable, then it can at least store one bit. If it is not …

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Understanding the maximum number of columns in a MySQL table

This post was initially going to be two sets of polls: “What is the maximum number of columns in MySQL?” and “What is the minimum maximum number of columns in MySQL?”. Before you read on, …

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Hidden columns of query_review_history table

You can use pt-query-digest to process a MySQL slow query log and store historical values for review trend analysis into query_review_history table. According to its official documentation you can populate many columns in that table …

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How number of columns affects performance ?

It is pretty understood the tables which have long rows tend to be slower than tables with short rows. I was interested to check if the row length is the only thing what matters or …

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Feature Idea: Finding columns which query needs to access

In query examinations it is often interesting which columns query needs to access to provide result set as it gives you ideas if you can use covering indexes to speed things up or even cache …

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Advanced Query Tuning in MySQL 5.6 and MySQL 5.7 Webinar: Q&A

Thank you for attending my July 22 webinar titled “Advanced Query Tuning in MySQL 5.6 and 5.7” (my slides and a replay available here). As promised here is the list of questions and my answers …

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