diff --git a/School/Development/Primary Key.md b/School/Development/Primary Key.md
index 53fc720..0d8f90c 100644
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@@ -1,2 +1,11 @@
 # Primary Key
-A Primary key is a [[Constraint]]  
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+A Primary key is a [[Constraint]] that uniquely identifies [[SQL Database#Entity]] in a entity set (table).
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+There can only be ONE primary per table and can consist of multiple attributes (columns).
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+A primary key is **not** required, but highly advised. Even if you don't use it its better to include one in your scheme.
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