The SQL DISTINCT clause allows us to remove redundant duplicate rows from our query results. For example if two rows contain the same values, then only one of them is returned.
But how does DISTINCT handle NULL values?
Let’s find out.
Continue readingIf you’re getting an error message that reads “The function ‘PERCENT_RANK’ must have an OVER clause with ORDER BY” in SQL Server, it’s probably because you’ve omitted the ORDER BY clause from the OVER clause when using the PERCENT_RANK() function.
The PERCENT_RANK() function requires an OVER clause that contains an ORDER BY clause. This error happens when we include the OVER clause but not the ORDER BY clause.
To fix this error, add an ORDER BY clause to the OVER clause.
If you’re getting an error in SQL Server that reads “The least function requires 1 to 254 arguments“, it’s probably because you’re either passing too few or too many arguments to the LEAST() function.
As the error message states, the LEAST() function requires at least 1 argument, and no more than 254 arguments.
To fix this issue, be sure to pass at least 1 argument, and no more than 254 arguments when using the LEAST() function.
In statistics, the mode is the most commonly occurring value in a data set. When using SQL databases, we can easily run a SQL query to find out the mode of a given column.
Below are several options we can use to calculate the mode in SQL.
Continue readingSuppose you’re trying to query column, but you need to set a minimum value to be returned, even if the column contains values that are less than that minimum. For example, you want a minimum value of 50 to be returned, even if the column contains values that are less than 50.
We can use the GREATEST() function to build such a query.
Most major RDBMSs support the DISTINCT clause, which allows us to get unique – or “distinct” – rows from our SQL queries. But PostgreSQL’s implementation of this clause has an extra option that most other RDBMSs don’t include.
PostgreSQL allows us to include the ON() option when using DISTINCT. This enables us to specify exactly which columns should be evaluated by the DISTINCT modifier, while simultaneously allowing us to return columns that aren’t evaluated.
If you’re getting a PostgreSQL error that reads “SELECT DISTINCT ON expressions must match initial ORDER BY expressions” when trying to run a query, it’s probably because the initial columns provided to your ORDER BY clause are different to the ones provided to the DISTINCT ON clause.
To fix this error, make sure the initial columns provided to the ORDER BY clause are included in the DISTINCT ON clause.
MySQL includes some nonaggregate window functions that allow us to get a value from a specific row. We can use such functions to do things like, compare the value in the specified row with the value in the current row, even if both values are in the same column.
Below are five functions that we can use to do this.
Continue readingMany RDBMSs have a LIMIT clause that allows us to limit the rows returned by a query to a specified number. SQL Server doesn’t have a LIMIT clause but it does have a TOP() function that allows us to do the same thing.
But Oracle Database has neither.
Fortunately, Oracle does have a number of options that allow us to get the same result.
Continue readingIf you’re getting error message 4112 that reads “The function ‘FIRST_VALUE’ must have an OVER clause with ORDER BY” when using the FIRST_VALUE() function, it’s probably because you’re omitting the ORDER BY clause from the OVER clause.
In SQL Server, the FIRST_VALUE() function requires an OVER clause that contains an ORDER BY clause. This error happens when we provide the OVER clause but not the ORDER BY clause.
To fix this error, simply add an ORDER BY clause to the OVER clause.