Mysql加入两个查询

Question

I have two queries:

SELECT opr, COUNT(*) FROM table WHERE field = 'YES' GROUP BY opr

SELECT opr, MAX(category) FROM table WHERE field = 'NO' GROUP BY opr

So basically in the first query I am getting the number of transactions a user makes. In the second query I am getting a category that all of those transactions fall under. I don't want to get all categories for each transaction they made, just the Max of the category field so that I have one entry per operator.

Until now, I have been catching both result sets in separate arrays and the looping through both arrays to get the complete opr->picks->category.

This doesn't always work it sometimes associates the wrong category to the wrong operator.

Is there a way to combine these two queries into one, so that I get the operator and picks, then the MAX(category)? The issue is that the conditions for each query are different on the field column.

Answer 1

SELECT opr, 
       COUNT(CASE WHEN field = 'YES' THEN 1 END) AS number_of_transactions,
       MAX(CASE WHEN field = 'NO' THEN category END) AS category
FROM table 
GROUP BY opr ;

Answer 2

The above logic can be attained in one query by using CASE

SELECT opr, COUNT(CASE WHEN `field` = 'YES' THEN opr END) as `count`, 
MAX(CASE WHEN `field` = 'NO' THEN category END) as `max`
FROM table   GROUP BY opr

Answer 3

Just add it in:

SELECT opr,count(*), MAX(category) FROM table WHERE field = 'YES' GROUP BY opr

You might also be able to drop it from 2 queries to 1 with this:

SELECT opr,count(*), MAX(category), field FROM table GROUP BY opr, field

Answer 4

even faster on the processor, use a sum bool:

select 
opr, 
sum(field='yes') as transactions, 
max(if(field='no',category, null)) as category
from table 
group by opr