Re: Improve examples for range operators

On Wed, Feb 20, 2019 at 12:27:26PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/11/functions-range.html
> Description:
> 
> Hi.
> 
> It would be nice if next examples:
> 
> << 	strictly left of 	int8range(1,10) << int8range(100,110) 	t
> >> 	strictly right of 	int8range(50,60) >> int8range(20,30) 	t
> &< 	does not extend to the right of 	int8range(1,20) &< int8range(18,20)
> 	t
> &> 	does not extend to the left of 	int8range(7,20) &> int8range(5,10) 	t
> 
> are extended by:
> **not** strictly left of, **not** strictly right of, **extends** to the
> right of, **extends** to the left of
> 
> Because without manual experiments I can not imagine the ranges that cause
> 'false' result for the examples above.

Well, they are not technically negatives of each other.  << means the
first is all left of the second, while &< means that it doesn't go to
the right of the second, e.g.,

	SELECT int8range(1,10) &< int8range(100,110);
	 ?column?
	----------
	 t
	
	SELECT int8range(1,105) &< int8range(100,110);
	 ?column?
	----------
	 t
	
	SELECT int8range(1,200) &< int8range(100,110);
	 ?column?
	----------
	 f

Notice it changed from true to false and none of these was strictly to
the right.

-- 
  Bruce Momjian  <[email protected]>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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