rank¶
This function is used to return the rank of a value in a set of values. When multiple values share the same rank, the next rank in the sequence is not consecutive.
Restrictions¶
The restrictions on using window functions are as follows:
Window functions can be used only in select statements.
Window functions and aggregate functions cannot be nested in window functions.
Window functions cannot be used together with aggregate functions of the same level.
Syntax¶
rank() over ([partition_clause] [orderby_clause])
Parameters¶
Parameter | Mandatory | Description |
|---|---|---|
partition_clause | No | Partition. Rows with the same value in partition columns are considered to be in the same window. |
orderby_clause | No | It is used to specify how data is sorted in a window. |
Return Values¶
The return value is of the INT type.
Note
If the value of a is NULL, NULL is returned.
Example Code¶
To help you understand how to use functions, this example provides source data and function examples based on the source data. Run the following command to create the logs table and add data:
CREATE TABLE logs (
cookieid string,
createtime string,
pv INT
) ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
stored as textfile;
Adds the following data:
cookie1 2015-04-10 1
cookie1 2015-04-11 5
cookie1 2015-04-12 7
cookie1 2015-04-13 3
cookie1 2015-04-14 2
cookie1 2015-04-15 4
cookie1 2015-04-16 4
cookie2 2015-04-10 2
cookie2 2015-04-11 3
cookie2 2015-04-12 5
cookie2 2015-04-13 6
cookie2 2015-04-14 3
cookie2 2015-04-15 9
cookie2 2015-04-16 7
Example: Groups all records by cookieid, sorts them by pv in descending order, and returns the sequence number of each row in the group. An example command is as follows:
select cookieid, createtime, pv,
rank() over(partition by cookieid order by pv desc) as rank
from logs
where cookieid = 'cookie1';
-- Result:
cookie1 2015-04-12 7 1
cookie1 2015-04-11 5 2
cookie1 2015-04-16 4 3 (third in parallel)
cookie1 2015-04-15 4 3
cookie1 2015-04-13 3 5 (skip 4 and start from 5)
cookie1 2015-04-14 2 6
cookie1 2015-04-10 1 7