Mysql按列分组并最好在另一列值上获得最大id

Question

I have a table with the content like this;

id      customer  is_default
1606384 5828      1
1573786 5828      0
1575316 5828      0
1817769 5828      0

For this customer, there is a is_default=1 address but some others there is none. For example;

id      customer  is_default
1806384 5829      0
1873786 5829      0
1875316 5829      0
1917769 5829      0

I'd like to get the MAX(id) but query should prefer is_default=1 first

So for example, in the first table query must return MAX(id) = 1606384 and for the second table should return MAX(id) = 1917769

I can't wrap my head around this.

Can you guys help me ?

Edit 1

Responding to comment of @Strawberry

I've tried this approach;

First I've multiplied the is_default with id and order by in order to get the max id from the query. But this was all wrong as now I understand

    SELECT MAX(id) as mid,MAX(is_default)
    FROM (
        (SELECT rel.maxid as id,customer,is_default FROM (
select (id+(is_default*10000000)) as maxid,customer,is_default FROM customer_address ORDER BY is_default DESC) rel ORDER BY maxid)
             ) rel
    GROUP BY customer

Answer 1

DROP TABLE IF EXISTS my_table;

CREATE TABLE my_table 
(id SERIAL PRIMARY KEY
,customer INT NOT NULL
,is_default TINYINT NOT NULL
);

INSERT INTO my_table VALUES
(1606384,5828,1),
(1573786,5828,0),
(1575316,5828,0),
(1817769,5828,0),
(1806384,5829,0),
(1873786,5829,0),
(1875316,5829,0),
(1917769,5829,0);

SELECT x.customer
     , COALESCE(MAX(y.id),MAX(x.id)) id 
  FROM my_table x 
  LEFT 
  JOIN my_table y 
    ON y.customer = x.customer 
   AND y.is_default = 1 
 GROUP 
    BY x.customer;
+----------+---------+
| customer | id      |
+----------+---------+
|     5828 | 1606384 |
|     5829 | 1917769 |
+----------+---------+

Answer 2

You could do the following but @Strawberry answer seems way better :

SELECT 
  customer, 
  (CASE WHEN is_default IS NOT NULL THEN is_default ELSE nis_default END) AS max
FROM (
SELECT 
  customer, 
  MAX(CASE WHEN is_default = 1 THEN id END) AS is_default, 
  MAX(CASE WHEN is_default = 0 THEN id END) AS nis_default
FROM t
GROUP BY customer) T

DEMO HERE

EDIT : My query can be simplified with COALESCE like this :

SELECT 
  customer, 
  COALESCE(
    MAX(CASE WHEN is_default = 1 THEN id END),
    MAX(CASE WHEN is_default = 0 THEN id END)) AS max
FROM t
GROUP BY customer

SECOND DEMO HERE

Answer 3

If you just want single max(id) value, preferably with is_default=1, then use:

select max_id
from (
  select is_default, max(id) as  max_id
  from customer_address
  group by is_default
  order by is_default desc
  limit 1
) as q;

Answer 4

You need a CASE expression:

select 
  customer, 
  case max(is_default) 
    when 1 then max(is_default * id) 
    else max(id)
  end maxid
from tablename 
group by customer

See the demo .
Results:

| customer | maxid   |
| -------- | ------- |
| 5828     | 1606384 |
| 5829     | 1917769 |

Answer 5

select MAX(ID),(select MAX(ID) from table where is_default = 0)
 from table
where is_default = 1