= is not always defined as equality is bad

Started by Zeugswetter Andreas DBTabout 28 years ago2 messages
#1Zeugswetter Andreas DBT
Andreas.Zeugswetter@telecom.at

Vadim wrote:

but this will be "known bug": this breaks OO-nature of Postgres,

because of

operators can be overrided and '=' can mean s o m e t h i n g (not

equality).

Example: box data type. For boxes, = means equality of _areas_ and =~
means that boxes are the same ==> =~ ANY should be used for IN.

Ok, here I think there should be a restriction to have the = operator
always be defined as equality operator. Because in the long run it will
be hard
to write equality restrictions. a = a1 and b =~ b1 and c +*#~ c1.
Also =, >, <, >= and the like will allways be candidates for use by the
optimizer
(boolean math to simplify restriction or to make an existing index
usable could be used).

I vote for: = must always be defined as equality in user defined types.

(if such comparison is not possible for a special type the = should not
be defined for it)
I therefore also suggest changing the box ops =~ to = and the area = to
some other sign.

Andreas

#2Bruce Momjian
maillist@candle.pha.pa.us
In reply to: Zeugswetter Andreas DBT (#1)
Re: [HACKERS] = is not always defined as equality is bad

Vadim wrote:

but this will be "known bug": this breaks OO-nature of Postgres,

because of

operators can be overrided and '=' can mean s o m e t h i n g (not

equality).

Example: box data type. For boxes, = means equality of _areas_ and =~
means that boxes are the same ==> =~ ANY should be used for IN.

Ok, here I think there should be a restriction to have the = operator
always be defined as equality operator. Because in the long run it will
be hard
to write equality restrictions. a = a1 and b =~ b1 and c +*#~ c1.
Also =, >, <, >= and the like will allways be candidates for use by the
optimizer
(boolean math to simplify restriction or to make an existing index
usable could be used).

I think each operator in pg_operator has a 'commutative' field for this:

| oprcom | oid | 4 |

--
Bruce Momjian
maillist@candle.pha.pa.us