To get combination of UPPER , lower and number random string length 4
Code:
SET @number:=4;
set @string:='';
SET @sql:=REPLACE('SET @t:=BENCHMARK(X,@string:=concat(@string,CASE char(FLOOR(49+ RAND()*3)) WHEN 1 THEN char(FLOOR(97+ RAND()*26)) WHEN 2 THEN char(FLOOR(65+ RAND()*26)) WHEN 3 THEN char(FLOOR(48+ RAND()*9)) END));','X',@number);
prepare stm1 from @sql;
execute stm1 ;
select @string; OUTPUT