The use of case-then techniques in SQL aggregate functions

We all know that when a case is applied in SQL, the information in the database is converted

For example, select (Case sex if 0 then ' men ' else ' end) as sex from Studentinfo

So what does it do in the aggregate function?

SELECTSex fromStudentSELECTSexCOUNT(*) asNum fromStudentGROUP  bySexSELECTSex,province,COUNT(*) asNum fromStudentGROUP  bysex,provinceSELECTSex,province,COUNT(province) asNum fromStudentGROUP  bysex,provinceSELECTSex,province,COUNT( CaseProvince when 'Zhejiang province'  Then 'Zhejiang province' ELSEProvinceEND) asNum fromStudentGROUP  bySexSELECTSexCOUNT( CaseProvince when 'Jiangxi Province'  Then 'Jiangxi Province' END) asJiangxi Province,COUNT( CaseProvince when 'Guangdong province'  Then 'Guangdong province' END) asGuangdong Province,COUNT( CaseProvince when 'Zhejiang province'  Then 'Zhejiang province' END) asZhejiang Province fromStudentGROUP  bySex

The use of case-then techniques in SQL aggregate functions