Updated March 8, 2023
Definition of Redshift Median
Redshift median function is used in the amazon redshift database server, using this function we can calculate median of range values. Null values from the specified column are ignored, if suppose our column contains the null value same value will be ignored by the median function in redshift. We can say that the median is the inverse function of distribution which assumes the model of continuous distribution. Median is the compute node function in the redshift database, this function will return an error when our query doesn’t refer to the user-defined or system table.
Syntax:
Below is the syntax of median in redshift.
1) Median (expression of median)
2) Select name_of_column1, name_of_column2, name_of_column3, …., median (name_of_column) from table_name group by clause order by clause
3) Median (expression of median)
Over (Clause) ( [ partition by (expression of partition) ] )
Parameters:
1) Median – Median is used to find the median of range values in amazon redshift. We can also use the partition by clause with median function in redshift.
2) Expression of median – This is nothing but the column name which was used as an expression name with median function in redshift. This column name provides the value, from those values we have determining the median.
3) Over – This clause is specifying the windows partitioning. This clause in the median function cannot contain the frame specification or window ordering.
4) Partition by – This is an optional clause while using median function in redshift. Using this clause we can set the range of values. We have using the expression with partition by clause.
5) Expression of partition – This is defined as the range value which was we have to give at the time of using partition clause using median in redshift. An expression is nothing but the set of record range for each group.
6) Name of column – This parameter is used in the select query to display the records from a specified column in redshift. We can use the number of columns with the select query in redshift.
7) Table name – This is nothing but the name of table from which we have retrieving the data using the median function in redshift.
8) Order by – Order by clause is used with median function to retrieve the data in ascending or descending order.
How median works in Redshift?
- We have using the column name with median function from this column name we have determine the median of values.
- The expression column name contains the data type as numeric or it will be explicitly converted into the numeric datatype. We cannot use another datatype column with median function in redshift.
- We need to use the group by clause at the time of using a median function in amazon redshift.
- At the time of using median function in redshift, we need to use numeric datatype column, we cannot use string value column in median function. If suppose we have used a string type column with the median function it will return the error as function not matching with the given name or we need to use an explicit type cast value.
- The below example shows that we need to use a numeric data type column with a median function in redshift.
- In the below example, we have used the username column with a median function, but this column contains the data type as a string. So it will give the error at the time of execution.
Code:
select userid, median(username) from users group by userid limit 10;
Figure – we need to use numeric data type column with median function in redshift.
- The return type of median expression in redshift is date, decimal and double. If suppose we have provided input value Int, numeric and decimal format then return type of median function is decimal.
- If suppose we have provided the input value as float and double then the return type of median function is double.
- If suppose we have provided the input value as date then return type of median function is date.
- If suppose we have defined the precision value as 38 or more then median function will return the error or inaccurate result.
- If suppose we have provided the input value as timestamp then return type of median function is timestamp.
- If suppose we have provided the input value as timestamptz then return type of median function is timestamptz.
- We can also use the order by clause with median function in redshift to display the records in ascending or descending order.
Examples
Below is the example of median in redshift.
1) Median function with group by clause
The below example shows that median function with group by clause. In this example, we have also used median column as userid.
Code:
select username, firstname, lastname, city, median (userid) as median_userid from users group by username, firstname, lastname, city;
Figure – Example of median function with group by clause.
2) Median function with limit clause
The below example shows that median function with a limit clause. In this example, we have also used median column as userid and limit as 3.
Code:
select username, firstname, lastname, city, median (userid) as median_userid from users group by username, firstname, lastname, city limit 3;
Figure – Example of median function with limit clause.
3) Median function with order by clause
The below example shows that median function with order by clause. In this example, we have also used median column as userid.
We can see that all the value of userid column will appear in ascending order, because by default value display in ascending order when we have not defined explicit order.
Code:
select username, firstname, lastname, city, median (userid) as median_userid from users group by username, firstname, lastname, city order by median_userid limit 5;
Figure – Example of median function with order by clause.
4) Median function with percentile cont
The below example shows that median function with percentile cont. In this example, we have also used median column as userid.
We have used percentile cont value as 1.0.
Code:
select username, firstname, lastname, city, percentile_cont (1.0) within group (order by userid), median (userid) from users group by username, firstname, lastname, city limit 5;
Figure – Example of median function with percentile cont.
Conclusion
Median function is used to find the median from the range of values in redshift. Median function is very useful in redshift. We have passing the column name which data type as numeric with median function. Return type of median function in redshift is decimal, double, date, and timestamp.
Recommended Articles
This is a guide to Redshift Median. Here we discuss the definition, syntax, How median works in Redshift? examples with code implementation. You may also have a look at the following articles to learn more –
