Select the nearest point for each row in table - mysql

Question

I use this to find the nearest point
SELECT
id,
ST_Distance(
POINT(52.760667210533,-7.22646337599035),
geo_point
) as distance
from Points
order by distance limit 1
I have a temp table TempPoints with all my candidate points and I want to normalise them onto OSM nodes, but there's lots, so I need a single query to resolve them all in one call. UNION wont let me use order by, and my DB raw query interface wont let me just fire a series of queries separated by ';'.
The temp table has lat and lon but can just as easily have a POINT. How can I go
select id,NearestTo(TempPoint.geo_point,Points) from TempPoints;
EDIT: I can parenthesise each select in my large union query, which solves my issue.
I would still like to be able to join on nearest row.

Answer 1

This might work for you:
SELECT t.id as tid, p.id as pid, p.geo_point
FROM TempPoint t
JOIN Points p ON p.id = (
SELECT p1.id
FROM Points p1
ORDER BY ST_Distance(p1.geo_point, t.geo_point)
LIMIT 1
)

Answer 2

My solution is to issue a series of queries, one for each row, and bind them together with a UNION. The mysql stack will blow eventually so you need to do them in blocks, but 1000 is OK on a default install.
You have to parenthesize the queries as they include an order by. Some points may fail so I label them all with a literal line_no sequence so you can edit and filter the originals. You also need to restrict the query with a
WHERE Contains(<polygon>,point)
clause, else it will try and sort the whole table, where polygon is a bounding box you have to cook up with GEOMFROMTEXT() and POLYGON(). And of course you need a special spatial index on the column!. Here's some code
var SMALL=0.001
var=query=points
.map(function(point){
var bottom=point.lat+SMALL
var top=point.lat-SMALL
var left=point.lon-SMALL
var right=point.lon+SMALL
var polygon=[
[bottom,left],
[top,left],
[top,right],
[bottom,right],
[bottom,left]
]
polygon="POLYGON(("+polygon.map(function(point){
return point.join(' ')
})
.join(",")+"))"
point.line_no=line_no++
return "(SELECT "+point.line_no+" as line_no,id, ST_Distance(POINT("+
point.lat+","+point.lon+
"),geo_point) as distance"+
" from Points "+
" WHERE Contains(GeomFromText('"+polygon+"'),geo_point) "+
" order by distance limit 1) "
})
.join(" UNION ")+" order by line_no"
return sequelize.query(query)