I'm confused of predicate and constraints.

What is the difference between these two?

Predicate and Constraints are two different things in SQL Server. There is no comparison between.

Refer the below to know more on the subject:

Predicate:

https://msdn.microsoft.com/en-us/library/ms189523.aspx?f=255&MSPPError=-2147217396

http://blogs.msdn.com/b/craigfr/archive/2006/07/07/652668.aspx

Constraints:

https://technet.microsoft.com/en-us/library/ms189862(v=sql.105).aspx

• Proposed as answer by Visakh16MVP 2 hours 8 minutes ago

Good day dy0803,

This is a bit like asking what is the difference between an animal and a dog :-)

Predicates are expression that evaluates to TRUE, FALSE, or UNKNOWN. CONTAINS is one of the Predicates that SQL Server provides.

Predicates are expressions that we can use them in WHERE clause. 

more info: Predicates

Constraints are used to check rules. 

more info: SQL Constraints