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| author | Marc G. Fournier | 1997-01-15 15:16:25 +0000 |
|---|---|---|
| committer | Marc G. Fournier | 1997-01-15 15:16:25 +0000 |
| commit | 59bb41a235761a605708e7d6387518ea178a72d5 (patch) | |
| tree | 03e1d79e2e428c9ac68bf0004dd92870c06bc3f5 /doc/manual/xoper.html | |
| parent | f02bd9335010684a64fcd9bc0f86615839d14fc4 (diff) | |
Import of PostgreSQL User Manual
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diff --git a/doc/manual/xoper.html b/doc/manual/xoper.html new file mode 100644 index 00000000000..10e5e203c1b --- /dev/null +++ b/doc/manual/xoper.html @@ -0,0 +1,70 @@ +<HTML> +<HEAD> + <TITLE>The POSTGRES95 User Manual - THE QUERY LANGUAGE</TITLE> +</HEAD> + +<BODY> + +<font size=-1> +<A HREF="pg95user.html">[ TOC ]</A> +<A HREF="xtypes.html">[ Previous ]</A> +<A HREF="xaggr.html">[ Next ]</A> +</font> +<HR> +<H1>9. EXTENDING SQL: OPERATORS</H1> +<HR> + POSTGRES supports left unary, right unary and binary + operators. Operators can be overloaded, or re-used + with different numbers and types of arguments. If + there is an ambiguous situation and the system cannot + determine the correct operator to use, it will return + an error and you may have to typecast the left and/or + right operands to help it understand which operator you + meant to use. + To create an operator for adding two complex numbers + can be done as follows. First we need to create a + function to add the new types. Then, we can create the + operator with the function. + +<pre> + CREATE FUNCTION complex_add(complex, complex) + RETURNS complex + AS '$PWD/obj/complex.so' + LANGUAGE 'c'; + + + CREATE OPERATOR + ( + leftarg = complex, + rightarg = complex, + procedure = complex_add, + commutator = + + ); +</pre> + + We've shown how to create a binary operator here. To + create unary operators, just omit one of leftarg (for + left unary) or rightarg (for right unary). + If we give the system enough type information, it can + automatically figure out which operators to use. + +<pre> + SELECT (a + b) AS c FROM test_complex; + + + +----------------+ + |c | + +----------------+ + |(5.2,6.05) | + +----------------+ + |(133.42,144.95) | + +----------------+ +</pre> +<HR> +<font size=-1> +<A HREF="pg95user.html">[ TOC ]</A> +<A HREF="xtypes.html">[ Previous ]</A> +<A HREF="xaggr.html">[ Next ]</A> +</font> +</BODY> +</HTML> + |