\(
\def\T#1{\bf #1}
\def\A#1{\rm #1}
\def\K#1{\underline{\bf #1}}
\def\Set#1{\cal #1}
\def\BSet#1{\boldsymbol{\cal #1}}
\def\nmapsto{\mathop{{\not}{\mapsto}}}
\def\except{-}
\def\tuple#1{\langle{\rm #1}\rangle}
\def\dollar{\$}
\def\IF{\boldsymbol{\leftarrow}}
\)
SQL: Constraints
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EECS-3421A: Introduction to Database Systems
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Fall 2024
The Syntax for Trigger in PostgrSQL
**Two kinds**:
*
_virtual:_
not stored in the database;
just a query for constructing the relation.
*
_materialized:_ actually constructed, stored, and _maintained_
like a table.