Generate grid line coordinates using SQL - sql

Question

Oracle 18c:
Using an SQL query, I want to generate a list of coordinates that make up the line segments of a square grid graph:
STARTPOINT_X STARTPOINT_Y ENDPOINT_X ENDPOINT_Y
------------ ------------ ---------- ----------
0 0 1 0 --horizontal lines
1 0 2 0
2 0 3 0
3 0 4 0
4 0 5 0
5 0 6 0
...
0 0 0 1 --vertical lines
0 1 0 2
0 2 0 3
0 3 0 4
0 4 0 5
0 5 0 6
...
[220 rows selected]
Details:
The lines would be split at each intersection. So, in the image above, there are 220 lines. Each line is composed of two vertices.
Ideally, I would have the option of specifying in the query what the overall grid dimensions would be. For example, specify this somewhere in the SQL: DIMENSIONS = 10 x 10 (or DIMENSIONS = 100 x 100, etc.).
To keep things simple, we can assume the grid's overall shape will always be a square (length = width). And we can make the cell size 1 unit.
I've supplied sample data in this db<>fiddle. I created that data using Excel.
Hint: The vertical grid lines start at row 111.
The reason I want to generate this data is:
I want sample line data to work with when testing Oracle Spatial queries. Sometimes I need a few hundred lines. Other times, I need thousands of lines.
Also, if the lines are in a grid, then it will be obvious if any lines are missing in my results (by looking at the data in mapping software and spotting gaps).
How can I generate those grid line coordinates using SQL?
Related: Generate grid line features using SQL

Answer 1

You can use:
WITH range (v) AS (
SELECT LEVEL - 1 FROM DUAL CONNECT BY LEVEL <= 11
)
SELECT x.v AS startpoint_x,
y.v AS startpoint_y,
x.v + 1 AS endpoint_x,
y.v AS endpoint_y
FROM range x CROSS JOIN range y
WHERE x.v <= 9
UNION ALL
SELECT x.v AS startpoint_x,
y.v AS startpoint_y,
x.v AS endpoint_x,
y.v + 1 AS endpoint_y
FROM range x CROSS JOIN range y
WHERE y.v <= 9
or, more generally:
WITH range (v) AS (
SELECT LEVEL - 1 FROM DUAL CONNECT BY LEVEL - 1 <= GREATEST(:max_x, :max_y)
)
SELECT x.v AS startpoint_x,
y.v AS startpoint_y,
x.v + 1 AS endpoint_x,
y.v AS endpoint_y
FROM range x CROSS JOIN range y
WHERE x.v < :max_x
AND y.v <= :max_y
UNION ALL
SELECT x.v AS startpoint_x,
y.v AS startpoint_y,
x.v AS endpoint_x,
y.v + 1 AS endpoint_y
FROM range x CROSS JOIN range y
WHERE x.v <= :max_x
AND y.v < :max_y
db<>fiddle here

Answer 2

There's a few ways to generate rows in Oracle. Note: This particular (recursive) way might not be optimal for very large grids, for that you might want to cross join 2 rows a bunch of times, however, this way is more amenable to injecting a variable for your dimension.
Selecting from the magic dual table usually returns 1 row but you can use the recursive connect by with the magic level value to determine how many rows you want. It doesn't return a 0-level so I hard-coded that in.
Looking at your square, its a mirror image made up of single unit vectors; all the horizontal vectors are repeated vertically, so only half have to be generated. Note the union all in the final query just returns the same data but swaps the x and y points.
It cross joins dimension CTE 3 times. The first 2 are to get the start & end and only a 3rd because for all the e.g. horizontal vectors we just want the vertical coordinates to be the same for both start and end. It filters out where start & end are equal as those are zero-length vectors which are not needed as well as those longer than length 1 using where b.point - a.point = 1 .
with dimension as (
select 0 as point from dual
union all
select level
from dual
connect by level <= 10
), points as (
select
a.point as startpoint,
b.point as endpoint,
c.point as fixed
from dimension a
cross join dimension b
cross join dimension c
where b.point - a.point = 1
)
select
startpoint as startpoint_x,
fixed as startpoint_y,
endpoint as endpoint_x,
fixed as endpoint_y
from points
union all
select
fixed as startpoint_x,
startpoint as startpoint_y,
fixed as endpoint_x,
endpoint as endpoint_y
from points
order by startpoint_y, endpoint_y, startpoint_x, endpoint_x
The place where you would inject the variable is on line 6, replacing that 10 with whatever grid size you want connect by level <= 10.
In a SQL*Plus script you could do that like
define dimension = 10;
with ...[ rest of the query blah blah ]
connect by level <= &dimension