{"id":3187,"date":"2025-06-06T02:09:47","date_gmt":"2025-06-06T02:09:47","guid":{"rendered":"https:\/\/diznr.com\/?p=3187"},"modified":"2025-06-06T02:09:47","modified_gmt":"2025-06-06T02:09:47","slug":"gate-cseit-database-hashing-example-which-clear-your-doubt-all","status":"publish","type":"post","link":"https:\/\/www.reilsolar.com\/pdf\/gate-cseit-database-hashing-example-which-clear-your-doubt-all\/","title":{"rendered":"GATE CSEIT\/Database\/Hashing example ( Which clear your all doubt)."},"content":{"rendered":"

GATE CSEIT\/Database\/Hashing example ( Which clear your all doubt).<\/p>\n

[fvplayer id=”291″]<\/p>\n

Hashing in Databases \u2013 GATE CSE\/IT Example with Explanation<\/strong><\/h3>\n

What is Hashing in Databases?<\/strong><\/h4>\n

Hashing is a technique used in databases to quickly access records<\/strong> using a hash function<\/strong> that maps keys to locations in a hash table. It helps in:
Efficient retrieval<\/strong> of data in O(1) average time complexity.
Reducing search time<\/strong> compared to sequential or binary search.
Handling large datasets<\/strong> effectively.<\/p>\n

Example 1: Simple Hashing in Database<\/strong><\/h3>\n

Problem Statement:<\/strong><\/h3>\n

A database contains student records with unique roll numbers (keys)<\/strong>. We use a hash function<\/strong> to store and retrieve records efficiently.<\/p>\n

Given Data:<\/strong><\/h3>\n
\n\n\n\n\n\n\n\n\n
Roll Number<\/th>\nName<\/th>\n<\/tr>\n<\/thead>\n
1023<\/td>\nAlice<\/td>\n<\/tr>\n
1045<\/td>\nBob<\/td>\n<\/tr>\n
1099<\/td>\nCharlie<\/td>\n<\/tr>\n
1121<\/td>\nDavid<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Hash Function:<\/strong><\/h3>\n

Let\u2019s use Modulo Hashing<\/strong> where the hash function is:<\/p>\n

h(Key)=Keymod\u2009\u200910h(Key) = Key \\mod 10<\/span>h<\/span>(<\/span>Key<\/span>)<\/span>=<\/span><\/span>Key<\/span><\/span>mod<\/span><\/span>10<\/span><\/span><\/span><\/span><\/span><\/p>\n

This means the roll number will be stored at an index based on its last digit.<\/p>\n

Hash Table After Insertion:<\/strong><\/h3>\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Index<\/th>\nStored Roll Numbers<\/th>\n<\/tr>\n<\/thead>\n
0<\/strong><\/td>\n–<\/td>\n<\/tr>\n
1<\/strong><\/td>\n1121<\/td>\n<\/tr>\n
2<\/strong><\/td>\n–<\/td>\n<\/tr>\n
3<\/strong><\/td>\n1023<\/td>\n<\/tr>\n
4<\/strong><\/td>\n–<\/td>\n<\/tr>\n
5<\/strong><\/td>\n1045<\/td>\n<\/tr>\n
6<\/strong><\/td>\n–<\/td>\n<\/tr>\n
7<\/strong><\/td>\n–<\/td>\n<\/tr>\n
8<\/strong><\/td>\n–<\/td>\n<\/tr>\n
9<\/strong><\/td>\n1099<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Example Query:<\/strong> Searching for roll number 1099<\/strong>
Step 1:<\/strong> Compute h(1099) = 1099 % 10 = 9<\/code>
Step 2:<\/strong> Go to index 9<\/strong> \u2192 Found! Charlie is stored here.<\/strong><\/p>\n

Example 2: Collision Handling with Chaining<\/strong><\/h3>\n

Problem Statement:<\/strong><\/h3>\n

Suppose two students have roll numbers 1023 and 1123<\/strong>. Since<\/p>\n

1023mod\u2009\u200910=1123mod\u2009\u200910=31023 \\mod 10 = 1123 \\mod 10 = 3<\/span>1023<\/span><\/span>mod<\/span><\/span>10<\/span>=<\/span><\/span>1123<\/span><\/span>mod<\/span><\/span>10<\/span>=<\/span><\/span>3<\/span><\/span><\/span><\/span><\/span><\/p>\n

both will be assigned to index 3<\/strong> in the hash table. This causes a collision<\/strong>.<\/p>\n

Solution:<\/strong><\/h3>\n

Use Chaining<\/strong> (Linked List at each index).<\/p>\n

Updated Hash Table (with Chaining for index 3):<\/strong><\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n
Index<\/th>\nStored Roll Numbers<\/th>\n<\/tr>\n<\/thead>\n
0<\/strong><\/td>\n–<\/td>\n<\/tr>\n
1<\/strong><\/td>\n1121<\/td>\n<\/tr>\n
2<\/strong><\/td>\n–<\/td>\n<\/tr>\n
3<\/strong><\/td>\n1023 \u2192 1123<\/td>\n<\/tr>\n
4<\/strong><\/td>\n–<\/td>\n<\/tr>\n
5<\/strong><\/td>\n1045<\/td>\n<\/tr>\n
6<\/strong><\/td>\n–<\/td>\n<\/tr>\n
9<\/strong><\/td>\n1099<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

\u00a0Now, when searching for 1123<\/strong>, we check index 3<\/strong> and traverse the list to find it.<\/p>\n

Key Takeaways for GATE Exam<\/strong><\/h3>\n

Direct Addressing<\/strong> is inefficient for large keys, so hashing<\/strong> is used.
Modular Hashing (h(key) = key % table_size<\/code>)<\/strong> is common in GATE problems.
Collisions are handled using:<\/strong><\/p>\n