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Why it is important to create unique key than composite key ?

In 1st Normalization form we create composite key. But why developers say that it is better to create unique key than composite . It is a relation of functional dependency?

tayyab ahmed
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    Umm, a "*composite key*" can also be a "*unique key*". Unique keys are not necessarily limited to a single column. Do you perhaps mean a "*uniquely generated single column key*"? Also known as a "*synthetic key*"? – RBarryYoung May 21 '15 at 14:28
  • composite keys are more difficult to join – jle May 21 '15 at 14:31
  • The phrase "unique key" is redundant; every "key" is unique. You seem to mean, a (redundant) surrogate key added to natural keys. Instead of "composite key" you probably mean "natural key(s) (only)". "A [surrogate key](https://en.wikipedia.org/wiki/Surrogate_key) may also be called a synthetic key, an entity identifier, a system-generated key, a database sequence number, a factless key, a technical key, or an arbitrary unique identifier." Ie non-"natural key" or non-"business key". Please edit your question. – philipxy Aug 03 '15 at 23:05
  • possible duplicate of [Surrogate vs. natural/business keys](http://stackoverflow.com/questions/63090/surrogate-vs-natural-business-keys) – philipxy Aug 03 '15 at 23:10

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