understanding rank and dense rank function

Author: techysanoj

rank_and_dense_rank_function_in_sql.sql

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+use world;
+
+show tables;
+
+select * from city;
+
+-- rank and dense rank function are used to give the rank to each row according to the order by clause for the rows
+-- order by is required but partition by is optional
+
+-- difference between rank and dense rank is that if the values are equal means rows order are equal then rank will skip the value but dense rank will not
+-- for eg: for rank: 1, 1, 3 (here rank 2 is missed) for dense_rank: 1, 1, 2 (here 2 is given)
+
+-- find the second highest population
+-- if the two countries have equal population then rank will not work so we will use dense_rank
+
+with results as(
+select name, countryCode,
+DENSE_RANK() over (order by population desc ) as rank_order
+from city)
+
+select * from results where rank_order = 2;
+
+-- now getting the all the cities according to the country code means for each country
+
+with results as (
+select name, countryCode, population,
+ DENSE_RANK() over (partition by countryCode order by population desc) as rank_order
+ from city
+)
+
+select * from results where rank_order = 2 order by countryCode;
+