Most of the major relational database management systems (RDBMSs) allow for a DISTINCT clause to be included in our SQL queries.
We use the DISTINCT keyword to return only unique rows. It eliminates duplicates from the results. If we have two or more rows with exactly the same data, we’ll only see one row in the results.
If you’re getting an error that reads “A TOP can not be used in the same query or sub-query as a OFFSET” when running a query in SQL Server, it’s probably because you’re using the TOP() clause and the OFFSET clause in the same query or sub-query.
We can’t use the TOP() clause and the OFFSET clause in the same query in SQL Server.
Below are three options for fixing this error.
Continue readingIf you’re getting an error that reads “The function ‘LAG’ must have an OVER clause” in SQL Server, it’s probably because you’re calling the LAG() function without an OVER clause.
The LAG() function requires an OVER clause (and that clause must have an ORDER BY clause).
To fix this issue, be sure to include an OVER clause when calling the LAG() function.
If you’re getting an error in PostgreSQL that reads something like “function lead(numeric, numeric) does not exist“, it may be because your second argument is of the wrong data type.
The second argument to the lead() function is optional, but if it’s provided, it must be an integer.
To fix this issue, make sure the second argument is an integer. Alternatively, you can omit the second argument altogether if you’re happy to use the default value of 1.
If you’re getting an error message that reads “The function ‘LEAD’ 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 LEAD() function.
The LEAD() 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.
Most RDBMSs have functions that make it easy to calculate the median value from a column in our queries.
Below are three SQL functions we can use to calculate the median value in a column.
Continue readingIf you’re getting an error that reads “function mode() does not exist” in PostgreSQL, it could be that you’re using the wrong syntax with this function.
The mode() function requires a WITHIN GROUP clause, and we can get the above error if we remove that clause.
In this case, we can fix the error by adding a valid WITHIN GROUP clause.
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.
When we create a window function in SQL, we have the option of defining it directly in the OVER clause or in a named window. When we define it in a named window, we can refer to that window name in our OVER clause, which saves us from having to define it directly in the OVER clause.
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.