a predicate is a property or an expression that either holds or doesn’t hold—in other words, is either true or false. The relational model relies on predicates to maintain the logical integrity of the data and define its structure. One example of a predicate used to enforce integrity is a constraint defined in a table called Employees that allows only employees with a salary greater than zero to be stored in the table. The predicate is “salary greater than zero” (T-SQL expression: salary > 0).
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