In MySQL scheduled events are tasks that run according to a given schedule. After creating a scheduled event, we can modify it using the ALTER EVENT statement. This statement allows us to change the event’s definition, change its schedule, enable/disable it, rename it, and more. It also allows us to move the event to another database.

To move an event to another database, we use the ALTER EVENT statement with the RENAME clause, prefixing the event name with the database name (using dot notation).

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When we create a scheduled event in MySQL it’s enabled by default. However, we do have the option of creating it in disabled status. We can also go back later and change an event’s status from enabled to disabled.

Given this fact, we may sometimes find ourselves wondering whether an event is currently enabled or disabled.

Below are three ways to go about checking an event for its enabled/disabled status.

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By default, scheduled events in MySQL are dropped from the system once they expire. That means that if the event’s schedule has completed, then the event is dropped.

But we can override this behaviour with the ON COMPLETION clause. Specifically we can specify ON COMPLETION PRESERVE to keep the event in the system after it has expired. By default, events have ON COMPLETION NOT PRESERVE added to their definition, which means they are dropped as soon as they expire. Using ON COMPLETION PRESERVE changes this so that they aren’t dropped when they expire.

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There are several ways to list out all scheduled events in MySQL. But sometimes we might want to limit the results to just those that are set to a given status. Sometimes we might only want to see a list of disabled events.

Below are two options we can use to return all disabled events.

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In MySQL the REPLACE statement is normally used to replace existing rows in a table. But it’s not limited to just replacing existing rows. There are times when REPLACE will also insert new rows. It all depends on the incoming data, as well as how the table is structured in relation to the incoming data.

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Suppose you have an existing MySQL event that has a comment. But the comment isn’t as helpful as you’d like it to be, and so you’d like to change it to something else.

This can be done easily with the ALTER EVENT statement along with the COMMENT clause. When we include the COMMENT clause in the ALTER EVENT statement, it replaces whatever comment was in the event with the new comment. If the event didn’t have a comment, then a new comment appears.

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MySQL provides us with the ability to create scheduled events – tasks that run according to a specified schedule. Scheduled events allow for the ability to add comments within the event. We can do this with the COMMENT clause.

We can include the comment when creating the event, or we can add one to an existing event.

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In MySQL, adding a composite primary key to an existing table is similar to adding a singular primary key. We define the primary key with the ALTER TABLE statement.

However, when adding a composite primary key we need to use the ADD PRIMARY KEY clause. We can’t define it at the column level. With singular primary keys on the other hand, we have the choice of using the ADD PRIMARY KEY clause or applying it at the column level.

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In MySQL, GIPK stands for generated invisible primary key. A GIPK is created whenever we create an InnoDB table without explicitly defining a primary key and when we have GIPKs enabled.

To enable GIPKs, we need to set our sql_generate_invisible_primary_key server system variable to ON. By default this is set to OFF, which means GIPKs are disabled by default.

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