MySQL UPDATE with multiple tables and derived calculation - mysql

Question

I'm in need of assistance with a MySQL UPDATE involving two tables and a calculated value. The biggest issue seems to be getting the derived value in place.
I need to calculate the DENS column based on the number of IDs in Table 2 (Total ID by FIPS / Table.POP)
Table 1
---------------------
| FIPS | POP | DENS |
---------------------
| 0001 | 100 | |
| 0002 | 25 | |
| 0003 | 500 | |
---------------------
Table 2
-------------
| ID | FIPS |
-------------
| 01 | 0001 |
| 02 | 0001 |
| 03 | 0002 |
| 04 | 0003 |
| 05 | 0003 |
| 06 | 0003 |
-------------
I can't figure out the syntax for the UPDATE statement to properly associate the count and subsequent calculation with the FIPS value.
I thought the following might work but it has not:
UPDATE Table1
SET Table1.DENS = (
SELECT (COUNT(DISTINCT Table2.id) / Table1.POP )
FROM Table2
WHERE Table2.FIPS = Table1.FIPS
)
Any help is appreciated!
EDIT: Desired result would look like:
----------------------
| FIPS | POP | DENS |
----------------------
| 0001 | 100 | 0.020 |
| 0002 | 25 | 0.040 |
| 0003 | 500 | 0.006 |
----------------------
The DENS is calulated from Table 2 and Table 1 (using POP: total IDs/POP = DENS) in that there are 2 IDs for FIPS 0001 (2/100 = 0.0200), 1 ID For FIPS 0002 (1/25 = 0.0400), and 3 IDs for FIPS 0003 (3/500 = 0.0060)

Answer 1

Try
UPDATE table1 t1
JOIN (
SELECT FIPS, count( distinct ID ) As DENS
FROM table2
GROUP BY FIPS
) t2
ON t1.FIPS = t2.FIPS
SET t1.DENS = t2.DENS
;

Answer 2

DROP TABLE IF EXISTS table1;
CREATE TABLE table1
(fips INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,pop INT NOT NULL
,dens DECIMAL(5,3) NULL
);
INSERT INTO table1 VALUES
(1,100,NULL),
(2,25,NULL),
(3,500,NULL);
DROP TABLE IF EXISTS table2;
CREATE TABLE table2
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,fips INT NOT NULL
);
INSERT INTO table2 VALUES
(1,1),
(2,1),
(3,2),
(4,3),
(5,3),
(6,3);
UPDATE table1 x
JOIN
( SELECT t1.fips,COUNT(t2.fips)/SUM(DISTINCT t1.pop) n FROM table1 t1 JOIN table2 t2 ON t2.fips = t1.fips GROUP BY t1.fips ) y
ON y.fips = x.fips
SET x.dens = n;
SELECT * FROM table1;
+------+-----+-------+
| fips | pop | dens |
+------+-----+-------+
| 1 | 100 | 0.020 |
| 2 | 25 | 0.040 |
| 3 | 500 | 0.006 |
+------+-----+-------+
...or something like that

Answer 3

Correct answer ended up being combination of both with the addition of the reset of innodb_lock_wait_timeout (set to 600)
SET SESSION innodb_lock_wait_timeout = 600
Final update code was:
UPDATE Table1 x
JOIN (SELECT t1.FIPS, COUNT(DISTINCT t2.ID)/t1.POP n
FROM Table1 t1
JOIN Table2 t2 ON t2.FIPS = t1.FIPS
GROUP BY t1.FIPS) y
ON y.fips = x.fips
SET x.DENS = n
Thanks to both Kordirko and Strawberry for the assist on this!