This tutorial explains the use of MySQL aggregate functions like AVG, COUNT, SUM, MAX, MIN with the help of simple examples. Aggregate functions are a bunch of methods that operate on a set of values. They can do calculations for us and then returns one final value. For example, you may like to compute the sum of the data values in a given field. The following are aggregate functions that we are covering in this tutorial. 1. COUNT function 2. MIN function 3. MAX function 4. SUM function 5. AVG function MySQL Aggregate Functions with Examples Before we go through

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This tutorial explains MySQL OPTIMIZE TABLE statement which defrags tables and recovers unused space. We’ll describe the complete usage of this method with the help of simple examples. If your database is receiving a lot of deletes and updates calls, then it might lead to fragmentation in your MySQL data files. Therefore, a lot of unused space would go in vain, and also put a high impact on the performance. So, experts recommend that you must defrag your MySQL tables regularly. Hence, we’ll today explain how to use the MySQL OPTIMIZE TABLE to defrag tables and free up space. MySQL OPTIMIZE

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This tutorial explains MySQL CONCAT() which is a built-in String function. It takes variable no. of strings as input and concatenates them together. We’ll describe the usages of this method with the help of simple examples. MySQL string concatenation is more user-friendly than other databases such as PostgreSQL or Oracle. They provide a string concatenation operator “||” instead of a proper function. However, MS SQL server does the same job using the addition arithmetic operator (+). 1. CONCAT() Syntax 2. CONCAT() Simple Examples 4. CONCAT() with Tables Let’s now go through each of the section one by one. MySQL CONCAT()

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This tutorial explains MySQL DROP TABLE statement which deletes the specified tables from the in-use database. We’ll describe several usages of this method with the help of simple examples. 1. DROP TABLE Syntax 2. DROP TABLE If Exist 3. DROP TABLE Matching Pattern 4. DROP TABLE Full Example Let’s now read and understand each of the section one by one. MySQL DROP TABLE statement As stated initially, the DROP TABLE is a built-in MySQL statement which removes a specified table from the database. So, let’s first check the details and see how to use the DROP command. But first, create

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This tutorial explains MySQL ABS() which is a Math/Trig function. It takes a number as input and determines its absolute (positive) value. We’ll describe the usages of this method with the help of simple examples. 1. ABS() Syntax 2. ABS() Simple Examples 3. ABS() for Expression 4. ABS() with Tables Let’s now go through each of the section one by one. MySQL ABS() Function As stated initially, ABS() is a built-in MySQL function which does some math calculation to derive the absolute value of a number. In Maths term, an absolute value represents the length of a number on the

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This tutorial explains MySQL DATE_ADD function which adds up a slice of time (in days/hours, e.g., 1 day or 10 days) to the given date. We’ll describe the complete date arithmetic of this method with the help of simple examples. 1. DATE_ADD() Syntax 2. DATE_ADD() with -ve Interval 3. DATE_ADD() for Invalid Date 4. DATE_ADD() for Auto Adjustment Let’s now go through each of the section one by one. MySQL DATE_ADD() Function As stated initially, DATE_ADD() is a built-in MySQL function which adds the specified no. of days to a given date. So, let’s now see the details and check

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MySQL How do you restore tablespace?

This is not new information but I have not covered it much so addressing it now for those that need it.

If you lose your ibd files... you lose your data. So if you have a copy of one available.. or even if you are syncing from another database you can still import it.  What/how do you lose tablespace?

Here is a simple example to recover tablespace.



mysql> Create database demo;

mysql> use demo;

mysql> CREATE TABLE `demotable` (
    ->   `id` int(11) NOT NULL AUTO_INCREMENT,
    ->   `dts` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    ->   PRIMARY KEY (`id`)
    -> ) ENGINE=InnoDB;


Now we store some data...

…

Thanks……Good stuff…..

So I realized I had not made a post about this after this situation that recently came up.

Here is the scenario: A backup was taken at midnight, they used MySQL dumps per database. Then at ten am the next day the database crashed. A series of events happened before I was called in, but they got it up to a version of the database with MyISAM tables and the IBD files missing from the tablespace.

So option 1, restoring from backup would get us to midnight and we would lose hours of data. Option 2, we reimport the 1000's of ibd files and keep everything. Then we had option 3, restore from backup, then apply the binlogs for recent changes.

To make it more interesting, they didn't have all of the ibd files I was told, and I did see some missing. So not sure how that was possible but option 2 became an invalid option. They, of course, wanted the least data loss possible, so we went with option 3.

…

(Image credit: Pixabay).

In my earlier post, I showed how MySQL, since version 8.0.14, has support for LATERAL derived tables. With LATERAL, a JOIN can have a second table – a subquery-based derived table – be defined based on values from columns of the first table, and thus be re-calculated for each row of the first table.…

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