As of MySQL 8.0.16, we can create CHECK constraints in MySQL. We can create them at the time of creating the table, or we can add the constraint later.
To add a CHECK constraint to an existing table, we can use the ALTER TABLE statement.
Category: Relational
SERIAL vs AUTO_INCREMENT in MySQL
If you’ve ever encountered a SERIAL column in a MySQL database, you might’ve wondered how it differs from an AUTO_INCREMENT column. After all, they both generate values that automatically increment?
Read on to find out what the difference is between SERIAL and AUTO_INCREMENT in MySQL.
3 JSON Utility Functions in MySQL
MySQL provides us with a few utility functions that act on JSON values, or strings that can be parsed as JSON values.
Below are three JSON utility functions that we can use for such tasks.
Continue readingHow to Add Headings for WITH ROLLUP in MySQL
MySQL provides us with the WITH ROLLUP modifier for the GROUP BY function for generating super aggregate data.
But by default, this modifier doesn’t label its data. By this I mean, it doesn’t provide us with meaningful labels for the rows that it generates. It simply uses NULL in those rows.
Maybe you’ve encountered this and are now looking for a solution.
Below is a handy little technique we can use to replace NULL with our own headings for these rows.
Using the sys.format_statement() Function in MySQL to Truncate a SQL Statement
In MySQL, the sys.format_statement() system function reduces the length of a given string/SQL statement to the length stored in the statement_truncate_len configuration option.
This function can be handy for truncating potentially long SQL statements retrieved from Performance Schema tables into a more suitable length (64 characters by default).
Continue readingHow to Create a CHECK Constraint Against a JSON Column in MySQL
When we create or modify a table in MySQL, we have the option of applying a CHECK constraint against one or more columns. This allows us to check the data before it enters the database. Data can only enter the database if it doesn’t violate the rules in our CHECK constraint.
If the column is a JSON column, we have the option of creating a CHECK constraint that checks that the JSON document doesn’t violate its JSON schema. To do this, we can include the schema in the CHECK constraint.
Understanding the PS_THREAD_ID() Function in MySQL
In MySQL, we can use the PS_THREAD_ID() function to get the Performance Schema thread ID assigned to a given connection ID. This can be useful whenever we use a function that takes the thread ID as its parameter, but we only know the connection ID.
If no thread ID exists for the connection, then NULL is returned.
The built-in PS_THREAD_ID() function does the same thing as the now deprecated sys.ps_thread_id() function. Therefore, we can call the function without needing to qualify it with sys or making sys our current schema.
Using the sys.format_path() Function to Dynamically Replace a Subpath with its Equivalent System Variable in MySQL
In MySQL, the sys.format_path() function is a stored function in the sys schema. It accepts a path name, and returns the modified path name after replacing subpaths that match the values of certain system variables.
So we can use the function to dynamically replace part or all of our path with a system variable that matches that path segment.
Continue readingUnderstanding the sys.extract_table_from_file_name() Function in MySQL
In MySQL, the sys.extract_table_from_file_name() function is a stored function in the sys schema.
It accepts a path name, and returns the path component that represents the table name.
Continue readingHow to Use the sys.ps_is_account_enabled() Function in MySQL
In MySQL, we can use the sys.ps_is_account_enabled() function to check whether Performance Schema instrumentation for a given account is enabled.
The function returns YES or NO, depending on whether or not the instrumentation for the given account is enabled.