Why are values inserted into postgis columns of type geometry in quotes?

Question

I'm figuring out how to use the PostGIS extension, and I found a nice tutorial: http://postgis.net/workshops/postgis-intro/geometries.html.

First the tutorial directs to create a table:

CREATE TABLE geometries (
    name varchar,
    geom geometry
);

Then insert into that table

insert into geometries (name, geom)
values
    ('Point', 'point(0 0)');

Then, looking at what other column types I can use with the PostGIS addon, I found that I can use the point type directly:

create table points (
    name varcar,
    point point
);
insert into points (name, point)
values 
    ('point 1', point(0, 1));

(Notice that the inserted value into the point column is NOT wrapped in quotes)

Trying to insert a point into the geometries table without wrapping the value in a quote fails:

insert into geometries (name, geom)
values
    ('Point', point(0 0));

SQL Error [42601]: ERROR: syntax error at or near "0"

This seems like it might be significant... If a column of type point allows for inserting values defined via that type (point(0 0)) - I assume this isn't a normal SQL function call? -, why can't I do the same for a column of type geometry?

Answer 1

the point is not a PostGIS type, but a native PostgresSQL type. The two are not compatible.

Creating a geometry from a string is one way. You can of course create a (PostGIS) point geometry via ST_Point or ST_MakePoint

select st_point(1,1);

Answer 2

For either type, you could insert with or without quotes. What caused the error was the missing comma (which is required only in SQL):

postgres=# select point(0 0);
ERROR:  syntax error at or near "0"
LINE 1: select point(0 0);
                       ^
postgres=# select point(0, 0);
 point
-------
 (0,0)
(1 row)

(For the geometry type, the point value would be automatically converted.)