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Joe Celko's SQL for Smarties, 5th Edition by Joe Celko

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Chapter 17

Comparison or Theta Operators

Abstract

Comparison or theta operators are used for joins and control the declarative statements in the language.

Keywords

Data type conversion

Data type promotion

IS <logical value>

IS [NOT] NORMALIZED

IS [NOT] NULL

Monadic operators

Row comparisons

Theta operators

Dr. Codd introduced the term “theta operators” in his early papers for what a programmer would have called a comparison predicate or operator. The large number of data types in SQL makes doing comparisons a little harder than in other programming languages; we have to do more casting. Values of one data type have to be promoted to values of the other data type before the comparison can be done. The available data types are implementation- ...

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