MySQL complex semi-join without group by - mysql

Question

Summary
I am looking for a semi-join(ish) query that selects a number of customers and joins their most recent data from other tables.
At a later time, I wish to directly append conditions to the end of the query: WHERE c.id IN (1,2,3)
Problem
As far as I am aware, my requirement rules out GROUP BY:
SELECT * FROM customer c
LEFT JOIN customer_address ca ON ca.customer_id = c.id
GROUP BY c.id
# PROBLEM: Cannot append conditions *after* GROUP BY!
With most subquery-based attempts, my problem is the same.
As an additional challenge, I cannot strictly use a semi-join, because I allow at least two types of phone numbers (mobile and landline), which come from the same table. As such, from the phone table I may be joining multiple records per customer, i.e. this is no longer a semi-join. My current solution below illustrates this.
Questions
The EXPLAIN result at the bottom looks performant to me. Am I correct? Are each of the subqueries executed only once? Update: It appears that DEPENDENT SUBQUERY is executed once for each row in the outer query. It would be great if we could avoid this.
Is there a better solution to what I am doing?
DDLs
DROP TABLE IF EXISTS customer;
CREATE TABLE `customer` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
);
DROP TABLE IF EXISTS customer_address;
CREATE TABLE `customer_address` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`customer_id` bigint(20) unsigned NOT NULL,
`street` varchar(85) DEFAULT NULL,
`house_number` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`id`)
);
DROP TABLE IF EXISTS customer_phone;
CREATE TABLE `customer_phone` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`customer_id` bigint(20) unsigned NOT NULL,
`phone` varchar(32) DEFAULT NULL,
`type` tinyint(3) unsigned NOT NULL COMMENT '1=mobile,2=landline',
PRIMARY KEY (`id`)
);
insert ignore customer values (1);
insert ignore customer_address values (1, 1, "OldStreet", 1),(2, 1, "NewStreet", 1);
insert ignore customer_phone values (1, 1, "12345-M", 1),(2, 1, "12345-L-Old", 2),(3, 1, "12345-L-New", 2);
SELECT * FROM customer;
+----+
| id |
+----+
| 1 |
+----+
SELECT * FROM customer_address;
+----+-------------+-----------+--------------+
| id | customer_id | street | house_number |
+----+-------------+-----------+--------------+
| 1 | 1 | OldStreet | 1 |
| 2 | 1 | NewStreet | 1 |
+----+-------------+-----------+--------------+
SELECT * FROM customer_phone;
+----+-------------+-------------+------+
| id | customer_id | phone | type |
+----+-------------+-------------+------+
| 1 | 1 | 12345-M | 1 |
| 2 | 1 | 12345-L-Old | 2 |
| 3 | 1 | 12345-L-New | 2 |
+----+-------------+-------------+------+
Solution so far
SELECT *
FROM customer c
# Join the most recent address
LEFT JOIN customer_address ca ON ca.id = (SELECT MAX(ca.id) FROM customer_address ca WHERE ca.customer_id = c.id)
# Join the most recent mobile phone number
LEFT JOIN customer_phone cphm ON cphm.id = (SELECT MAX(cphm.id) FROM customer_phone cphm WHERE cphm.customer_id = c.id AND cphm.`type` = 1)
# Join the most recent landline phone number
LEFT JOIN customer_phone cphl ON cphl.id = (SELECT MAX(cphl.id) FROM customer_phone cphl WHERE cphl.customer_id = c.id AND cphl.`type` = 2)
# Yay conditions appended at the end
WHERE c.id IN (1,2,3)
Fiddle
This fiddle gives the appropriate result set using the given solution. See my questions above.
http://sqlfiddle.com/#!9/98c57/3

Answer 1

I would avoid those dependent subqueries, instead try this:
SELECT
*
FROM customer c
LEFT JOIN (
SELECT
customer_id
, MAX(id) AS currid
FROM customer_phone
WHERE type = 1
GROUP BY
customer_id
) gm ON c.id = gm.customer_id
LEFT JOIN customer_phone mobis ON gm.currid = mobis.id
LEFT JOIN (
SELECT
customer_id
, MAX(id) AS currid
FROM customer_phone
WHERE type = 2
GROUP BY
customer_id
) gl ON c.id = gl.customer_id
LEFT JOIN customer_phone lands ON gl.currid = lands.id
WHERE c.id IN (1, 2, 3)
;
or, perhaps:
SELECT
*
FROM customer c
LEFT JOIN (
SELECT
customer_id
, MAX(case when type = 1 then id end) AS mobid
, MAX(case when type = 2 then id end) AS lndid
FROM customer_phone
GROUP BY
customer_id
) gp ON c.id = gp.customer_id
LEFT JOIN customer_phone mobis ON gp.mobid = mobis.id
LEFT JOIN customer_phone lands ON gp.lndid = lands.id
WHERE c.id IN (1, 2, 3)
;
see: http://sqlfiddle.com/#!9/ef983/1/