Cześć!
Odnośnie wyszukania najbliższych średnic można np. zastosować taki sposób:
CREATE DATABASE IF NOT EXISTS test;
USE test;
CREATE TABLE IF NOT EXISTS foo (id INT, phi FLOAT);
TRUNCATE foo;
INSERT INTO foo VALUES (1, 23.29);
INSERT INTO foo VALUES (2, 91.33);
INSERT INTO foo VALUES (3, 78.45);
INSERT INTO foo VALUES (4, 25.26);
INSERT INTO foo VALUES (5, 11.13);
INSERT INTO foo VALUES (6, 3.22);
INSERT INTO foo VALUES (7, 24.88);
INSERT INTO foo VALUES (8, 25.22);
INSERT INTO foo VALUES (9, 48.44);
INSERT INTO foo VALUES (10, 38.39);
SET @pattern = 25.24;
SELECT id, phi, ABS(phi - @pattern) AS distance
FROM foo
ORDER BY distance
LIMIT 1
M.