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<chapter id="sql-syntax">
you will sometimes need to add parentheses when using combinations
of binary and unary operators. For instance
<programlisting>
-SELECT 5 ! + 6;
+SELECT 5 ! - 6;
</programlisting>
will be parsed as
<programlisting>
-SELECT 5 ! (+ 6);
+SELECT 5 ! (- 6);
</programlisting>
because the parser has no idea -- until it is too late -- that
<token>!</token> is defined as a postfix operator, not an infix one.
To get the desired behavior in this case, you must write
<programlisting>
-SELECT (5 !) + 6;
+SELECT (5 !) - 6;
</programlisting>
This is the price one pays for extensibility.
</para>