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# What is a Hash Key?

A hash key is a small value that is used to represent a large piece of data in a hash system.
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• Written By: M. McGee
• Edited By: Lauren Fritsky
• Last Modified Date: 14 June 2015
2003-2015
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A hash key is a small value that is used to represent a large piece of data in a hash system. A hash function is a mathematical equation that simplifies large amounts of data into small values. This process saves space in a database and makes retrieving information faster and easier for the programs. It is also common to use hash systems to locate repeating information in complex systems, like a repeated voice or image pattern or even repeated portions of a genome or deoxyribonucleic acid DNA strand. In addition, hash key is the international English term for the # key on a telephone or keyboard.

A hash system works via a mathematical system that turns information into a series of numerical hash keys. The original information for each hash key is saved in a listing called a hash table. When a system looks for information, but finds a key instead, it simply cross-references the key with the table and retrieves the original information.

When used in a database, a hash system is used for efficiency and speed. These systems simplify large amounts of information down into smaller bits, a process that both saves space in the database and reduces the amount of time required to send information. For instance, the name John Smith may appear over and over again in a database. The hash system may represent that specific string of letters with the value '01.'

In the above example, John Smith consists of ten characters, with the space included, and 01 is only two. When the database goes for the information and the hash key 01 comes back, it will check its hash table and send out ‘John Smith.’ Since the hash key is only 20% of the actual value of the information, it saves space on every occurrence of the information; it also saves that much time in transmission.

Other systems will use a hash key to find redundant data. When a system contains huge amounts of data that need sorting for redundancies or patterns, it is often easier to hash the information rather than sort it by hand. Since different hashing algorithms collapse information in different ways, the data is generally sent through several hashing methods. When the hashing is complete, it is possible to find patterns very quickly using the resulting hash tables.

In the United States, this key is generally called the pound key, and the symbol is a pound sign or a number sign. In Canada, the key is often called a number key. Nearly the entire English-speaking world outside of North American calls it the hash key.