The difference between clustured and non clustured index in Sql Server. Mainly Indexes are formed to speed up performance of a database as indexing a coloumn or group of coulmns will make a copy of that data in the local server, thereby reducing round trips, performance effect on the server and time taken. Disadvantages are that they occupy database space and that would require additional hardware costs. Clustured index in Sql Server takes up more space than non clustured indexes. Clustured indexes are like a HashTree everything is in a arranged order. It replicates the behaviour of the column which is to be indexed extactly the way it is in the table. also clustured index rearranges the way records are stored in a table putting them in order(key,value). a table can have only one clustured index. The leaf node of a clustured index contain data pages. In Non clustured index the logical order of the index does not match the way data is actually arranged in the data, it is like a hashmap. It takes less space, a table can have more than one non clustured index.The leaf node of a non clustured index does not contain data pages but index rows.