Indexes and Convert_Implicit

 When you are designing your where clause to access data from a given set of tables it would benefit you to pay careful attention to the data types of the columns you will be using.  SQL Server tries to help out by implicitly converting between data types which can cause 'hidden' optimizer issues.

A common example is the implicit conversion between character and integer datatypes.  Listed below is a snippet of the query I was asked to tune.

Cryptographic Hash Functions

Cryptographic hash functions take an arbitrary number of input bytes and reduce it to a fixed size. This resultant size is dependent upon the function you use, be it MD4,MD5,SHA-1, etc. I prefer to use SHA-1 since it is the most secure of the 3 listed above. There are many other cryptographic functions, but they are not included in all libraries.