optimize query with date type field in mysql

问题

I currently have the following query prepared:

select sum(amount) as total 
  from incomes 
 where (YEAR(date) = '2019' and MONTH(date) = '07') 
   and incomes.deleted_at is null

when reviewing it a bit, notice that it takes too long to have a lot of data in the table, since it goes through all this. I do not know much about optimizing queries, but I want to start documenting and researching for this case, reading a little note that although it is possible to create an index for a date type field, MySQL will not use an index once a column of the WHERE clause is wrapped with a function in this case YEAR and MONTH. So is this correct? What steps should I follow to improve its performance? Should I try to restructure my query?

回答1:

I would suggest writing the query as:

select sum(i.amount) as total
from incomes i
where i.date >= '2019-07-01' and
      i.date < '2019-08-01' and
      i.deleted_at is null;

This query can take advantage of an index on incomes(deleted_at, date, amount):

create index idx_incomes_deleted_at_date_amount on incomes(deleted_at, date, amount)

来源：https://stackoverflow.com/questions/56959725/optimize-query-with-date-type-field-in-mysql