index is... an index !
UNIQUE is an index which won't allow duplicate values (except for NULLS)
PRIMARY KEY is exactly like UNIQUE NOT NULL, with the bonus that the
database knows this column is the primary key so you can use stuff like
NATURAL JOIN without telling which column you want to use.
What are the major differences between Unique, primary index & just
plain index?
When creating tables I nominate one of these, but not sure what the
difference is?
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