MySQL

4 Ways to Replace NULL with a Different Value in MySQL

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In MySQL, sometimes you don’t want NULL values to be returned as NULL. Sometimes you want NULL values to be returned with a different value, such as “N/A”, “Not Applicable”, “None”, or even the empty string “”.

Fortunately there are several ways to do this in MySQL.

Here are four:

  • The IFNULL() function
  • The COALESCE() function
  • The IF() function combined with the IS NULL (or IS NOT NULL) operator
  • The CASE expression combined with the IS NULL (or IS NOT NULL) operator

Examples of these options are below.

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MySQL Group_Concat() vs T-SQL String_Agg()

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One of the T-SQL functions introduced in SQL Server 2017 is the STRING_AGG() function. This is basically the equivalent of MySQL’s GROUP_CONCAT() function – it lets you return query results as a delimited list, rather than in rows.

But there are a few minor differences between the two functions.

This article explores some of the main syntax differences between these functions.

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How to Return Query Results as a Comma Separated List in MySQL

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In MySQL, you can return your query results as a comma separated list by using the GROUP_CONCAT() function.

The GROUP_CONCAT() function was built specifically for the purpose of concatenating a query’s result set into a list separated by either a comma, or a delimiter of your choice.

This article provides examples of how it all works.

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MySQL COUNT() – Get the Number of Rows to be Returned by a Query

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MySQL includes a COUNT() function, which allows you to find out how many rows would be returned from a query. This function is part of the SQL standard, and it can be used with most relational database management systems.

The COUNT() function can also be used to affect the results of a query if required, for example, by only returning those results that have a row count greater than a given amount.

This article contains examples of COUNT() usage in MySQL.

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How to Check the Size of All Tables within a Database in MySQL

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In MySQL, you can check the size of all tables within a given database (or on all databases) by querying the information_schema.tables table. This table stores data about each table in a database, including information about each table’s size, creation date, collation, etc.

You can also find the size of each table within a database by using the MySQL Workbench GUI.

This article provides a quick overview of each method.

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How to Check the Size of a Database in MySQL

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In MySQL, you can query the information_schema.tables table to return information about the tables in a database. This table includes information about the data length, index length, as well as other details such as collation, creation time, etc. You can use the information in this table to find the size of a given database or all databases on the server.

You can also use the MySQL Workbench GUI to find details about the database (including its size).

This article provides a quick overview of both methods.

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AVG() – Calculate the Average Value of a Column in MySQL

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When using MySQL, you can use the AVG() function to calculate the average value from a range of values.

For example, you can use this function to find out what the average city population is for a given country or state. Given a country will have many cities, each with different populations, you can find out what the average is between them. One city might have a population of say, 50,000 while another has a population of 500,000. The AVG() function will calculate the average for you.

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How to Convert a String to Hexadecimal in MySQL – HEX()

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In MySQL, you can convert a string to its hexadecimal representation by using the HEX() function.

The HEX() function works on both strings and numbers, however, its handling of each of these is slightly different. When used to convert a number, it returns a hexadecimal string representation of the number treated as a longlong (BIGINT) number. But when converting a string, it returns a hexadecimal string representation of the string where each byte of each character is converted to two hexadecimal digits.

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3 Ways to “Unhex” a String in MySQL

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MySQL includes various functions that can assist you when working with hexadecimal values. One of the most obvious functions is the HEX() function, which enables you to convert a string into its hexadecimal equivalent.

However, there may be times where you want to convert a hexadecimal string back to a more readable string. That’s what this article is about.

Here are three ways to “unhex” a string in MySQL:

  • The UNHEX() function
  • The X hexadecimal notation
  • The 0x notation

Below are examples of each of these methods.

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