Mysql Case when usage

Select
SUM (1) as col_0_0_, sum (case vciinfo.useable when-1 then 1 else 0 end) as col_1_0_,
SUM (case when vciinfo.activatetime was null then 0 else 1 end) as col_2_0_
From Vci_info Vciinfo

This is a SQL statement that implements the number of different state data in the statistics table with case

It is important to note that if the field is empty, the case will be vciinfo.activatetime is null

Judgment value Case vciinfo.useable when-1

When the position is different

Mysql Case when usage