查询lat long没有返回任何结果mysql

I have this table.

wppl_friends_locator

The table have columns named

lat float(10,6)

long float(10,6)

These columns have lat and long saved of entries, now i am trying to get results within radius of 30 miles from a given lat,long.

Sql does not return any results for some reasons which i am unable to figure out, below is the sql

SELECT
    member_id,
    (3959 * ACOS(
        COS(RADIANS(-19.943379)) *
        COS(RADIANS('lat')) *
        COS(RADIANS('long') - RADIANS(-43.9521885)) +
        SIN(RADIANS(-19.943379)) *
        SIN(RADIANS('lat'))
    )) AS distance
FROM
    wppl_friends_locator
HAVING
    distance < 30
ORDER BY
    distance;

so even if i do an entry in this table with same lat long which I am providing in sql query, It still does not return any results.

I have been stuck on it for few days, any help would be appreciated.

Table structure