In MySQL, the FIRST_VALUE() function is a window function that returns the value of the given expression from the first row of the window frame.
Category: MySQL
Understanding the DENSE_RANK() Function in MySQL
In MySQL, the DENSE_RANK() function is a window function that returns the rank of the current row within its partition, without gaps.
By “without gaps” this means that it returns contiguous rank numbers whenever there are peers. Peers are considered ties and receive the same rank. In such cases, the next rank value is one greater than the current one (i.e. the one that the peers receive).
Continue readingUnderstanding the RANK() Function in MySQL
In MySQL, RANK() is a window function that returns the rank of the current row within its partition, with gaps.
By “gaps” this means that it returns noncontiguous rank numbers whenever there are peers. Peers are considered ties and receive the same rank, but in such cases, we get a gap between this rank value and the next rank value.
Continue readingUnderstanding the PERCENT_RANK() Function in MySQL
In MySQL, PERCENT_RANK() is a window function that returns the percentage of partition values less than the value in the current row, excluding the highest value.
We can use PERCENT_RANK() to evaluate the relative standing of a value within a query result set or partition. Return values range from 0 to 1.
Understanding the CUME_DIST() Function in MySQL
In MySQL, CUME_DIST() is a window function that returns the cumulative distribution of a value within a group of values. This is the percentage of partition values less than or equal to the value in the current row. The return values range from 0 to 1.
Fix ERROR 3579 “Window name ‘…’ is not defined” in MySQL
If you’re getting error 3579 in MySQL, which reads something like “Window name ‘wf3’ is not defined“, it’s probably because you’re referring to a named window that doesn’t exist.
To fix this issue, make sure you refer to a named window that exists.
Continue readingUnderstanding the sys.sys_get_config() Function in MySQL
In MySQL, we can use the sys.sys_get_config() function to get a configuration option value from the sys_config table.
Fix ERROR 3580 “There is a circularity in the window dependency graph” in MySQL
If you’re getting error 3580 in MySQL, which reads “There is a circularity in the window dependency graph“, it’s probably because you’re using named windows that refer to each other in a way that creates a circular reference.
To fix this issue, make sure you don’t create a circular reference when referring to multiple named windows.
Continue readingHow to Change a CHECK Constraint’s Enforcement State in MySQL
When we create or alter a CHECK constraint in MySQL, we have the option of setting it to ENFORCED or NOT ENFORCED. This determines whether or not MySQL will enforce the rules of the constraint whenever data that violates the constraint tries to enter the database.
We can use the ALTER TABLE statement to change the enforcement state of an existing CHECK constraint in MySQL, as shown in the following example.
Fix ERROR 1140 “In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column…” in MySQL
If you’re getting MySQL error 1140, which reads something like “In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column ‘world.City.District’; this is incompatible with sql_mode=only_full_group_by“, it could be that you need to introduce a window function to the query.
This error can happen when we want multiple rows to contain aggregate values. For example, we might want to return subtotals of all rows within a group of rows. A window function can help us achieve this outcome.
Continue reading