Database Management Systems
If you’re getting an error that reads “The function ‘ROW_NUMBER’ must have an OVER clause” in SQL Server, it’s probably because you’re calling the ROW_NUMBER() function without an OVER clause.
Window functions such as ROW_NUMBER() require an OVER clause (and that clause must have an ORDER BY clause).
To fix this issue, add an OVER clause when calling the ROW_NUMBER() function.
If you’re getting an error that reads “The function ‘DENSE_RANK’ must have an OVER clause with ORDER BY” in SQL Server, it’s probably because you’re calling the DENSE_RANK() function without an ORDER BY clause.
Window functions such as DENSE_RANK() require an OVER clause, and that clause must have an ORDER BY clause. If you’re getting the above error, it’s likely that you’re providing an OVER clause, but you’re omitting the ORDER BY clause.
To fix this error, add an ORDER BY clause to the OVER clause.
Normally if we try to insert data that violates a CHECK constraint in MySQL, we get an error, and the whole INSERT operation fails (including any conforming rows).
But it’s possible to change this, so that any conforming rows are inserted, and only the non-conforming rows are skipped.
We can do this by using the IGNORE clause.
In PostgreSQL the last_value() function returns the value from the last row of the current window frame.
There are at least a couple of reasons you might get an error that reads “function nth_value(numeric) does not exist” in PostgreSQL.
It could be that you’re calling the nth_value() function without the correct number of arguments. It could also be that you’re passing the wrong argument type.
To fix this issue, be sure to pass the correct number of arguments, with the correct type.
Continue readingIn PostgreSQL the first_value() function returns the value from the first row in the current window frame.
We can use this function to get the value from the first row in a result set, or from the first row in the current partition, or some other window frame that’s been specified.
Continue readingIn MySQL, we can use the sys.ps_is_consumer_enabled() function to check whether a given Performance Schema consumer is enabled.
The function returns YES or NO, depending on whether or not the specified Performance Schema consumer is enabled. It returns NULL if the argument is NULL.
PostgreSQL has an ordered-set aggregate function called mode() that allows us to get the mode from a given column.
The mode is the most frequently occurring value.
Null values are ignored, so if null occurs the most, the mode() function will return the second most common value.
If you’re getting an error that reads “ERROR: invalid input syntax for type integer” in PostgreSQL, it’s probably because you’re calling the ntile() function with an argument of the wrong data type.
This error can occur when we pass the wrong type to the ntile() function. We can get a different error depending on the type, but this error can occur when we pass a string.
To fix this issue, be sure to pass a positive integer to the function.
Continue readingIn MariaDB, the MEDIAN() function returns the median value of a range of values.
We can use the MEDIAN() function in our queries to get a column’s median value across its partition or the whole result set.