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 readingWe can use SQL to create a running total of a given column. By this I mean, we can create a column that calculates the cumulative sum of a given column.
The running total/cumulative sum is the sum of all rows up until the current row. The result is that the sum increases (or decreases in the case of negative values) with each row returned in the result set. Each row’s value is added to the cumulative amount from all prior rows, so for any given row, we get the total sum for all rows up to that point – the “running total”.
Continue readingIn MySQL, we can use the sys.sys_get_config() function to get a configuration option value from the sys_config table.
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 readingIn SQL, we can use the following method to compute the number of items within a given range when using a window function.
By this I mean we can use a frame clause in the window function to output how many items have a value that’s in a similar range to the value in the current row.
Continue readingWhen 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.
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 readingWhen we use an OVER() clause to create a window function in SQL, we often use a PARTITION BY clause to partition the results. This can be handy if we want to do stuff like calculate subtotals.
But we can also use an empty OVER clause to calculate a grand total.
We might want to do this if we’re already using another OVER clause to calculate subtotals, but we also want a column to provide the grand total.
We can use the OVER() clause to create window functions in our SQL queries. A window function can be a useful tool that allows us to do things like compute moving averages, rank items, calculate cumulative sums, and much more.
Another common task for a window function might be to compute subtotals.
Continue readingWhen we create a CHECK constraint in MySQL, we have the option of defining it as ENFORCED or NOT ENFORCED.
MySQL CHECK constraints are enforced by default, so unless we explicitly define the constraint as NOT ENFORCED, it will automatically be enforced.
In any case, we can use either of the following two methods to check whether or not an existing CHECK constraint is enforced.