Обсуждение: Getting X coordinate from a point(lseg), btw i read the man page about points.
Getting X coordinate from a point(lseg), btw i read the man page about points.
Hi in the main page about geometric operations said:
It is possible to access the two component numbers of a point as though it were an array with indices 0 and 1. For example, if t.p is a point column then SELECT p[0] FROM t retrieves the X coordinate and UPDATE t SET p[1] = .. changes the Y coordinate. In the same way, a value of type box or lseg can be treated as an array of two point values. 1st. i have a field Column | Type | Modifiers
-----------+-----------------------+-------------------------------
id | integer | not null
info | lseg | After read the above, i tried to select info from table limit 1; info ---------------------------------------------------- [(647753.125,2825633.75),(647738.8125,2825626.75)]
the value i want to get is: 647753.125
so i tried to do: select info[0] from table limit 1; info ------------------------- (647753.125,2825633.75) i still want to get 647753.125, so i did:
select info[0][0] from table limit 1;
info
------
(1 row)
But, nothing appears like a NULL.
then i did: select point(info[0])[0] from table limit 1; ERROR: syntax error at or near "[" LINE 1: select point(info[0])[0] from table limit 1; and finally i wrote this mail :-) Regards. El contenido de este correo electrónico y sus archivos adjuntos son privados y confidenciales y va dirigido exclusivamente a su destinatario. No se autoriza la utilización, retransmisión, diseminación, o cualquier otro uso de esta información por un receptor o entidades distintas al destinatario. Si recibe este correo sin ser el destinatario se le solicita eliminarlo y hacerlo del conocimiento del emisor. La empresa no se hace responsable de transmisiones o comunicaciones no autorizadas o emitidas por personas ajenas a sus colaboradores utilizando éste medio electrónico.
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"Ing.Edmundo.Robles.Lopez" <erobles@sensacd.com.mx> writes:
> Hi in the main page about geometric operations said:
> It is possible to access the two component numbers of a point as though it were an array with indices 0 and 1. For
example,if t.p is a point column then SELECT p[0] FROM t retrieves the X coordinate and UPDATE t SET p[1] = ...
changesthe Y coordinate. In the same way, a value of type box or lseg can be treated as an array of two point
values.
> [ So how to get p2.x from an lseg value? ]
> select info[0] from table limit 1;
> (647753.125,2825633.75)
Right, that gets you a point.
> i still want to get647753.125, so i did:
> select info[0][0] from table limit 1;
Close, but that notation only works for a 2-dimensional array, which an
lseg is not. What you need is
regression=# select (info[0])[0] from table;
f1
------------
647753.125
(1 row)
The parenthesized object is a point, and then an entirely separate
subscripting operation has to be applied to it to get its X coordinate.
> then i did:
> select point(info[0])[0] from table limit 1;
Well, that's unnecessary since info[0] is already a point, but the
syntactic problem is again that you have to parenthesize the thing that
the second subscript is being applied to:
select (point(info[0]))[0] from table limit 1;
You need parentheses any time you're going to apply subscripting or
field selection to something that isn't a simple variable reference.
regards, tom lane