I would like to make a SELECT query which group by 3 first varchars ond shows it onces for each. for example the table "tblanimals":

id      name   age
--      ----   ---
1       DOG1   10
2       DOG2   12
3       DOG3   14
4       CAT1   16
5       CAT2   18

the output should be:

DOG
CAT

after it I need to make another (inside loop) simple query to show the details of each result from the last query we made:

DOG   DOG1   10
      DOG2   12
      DOG3   14
CAT   CAT1   16
      CAT2   18

10X

This query would help you:

Fiddle : here

select 
(
case i.rank
when 1 then i.subname
else '' end
) groupname,
i.name,i.age
from

 (SELECT SUBSTRING(`NAME`,1,3)AS SUBNAME, t.name,t.AGE ,

       ( 
            CASE SUBSTRING(`NAME`,1,3) 
            WHEN @curType 
            THEN @rownum := @rownum + 1 
            ELSE @rownum := 1 AND @curType := (SUBSTRING(`NAME`,1,3)) END
          )+1 AS rank

  FROM TEST t, 
       (SELECT @rownum := 0, @curType := '') r
  ) i

OUTPUT:

GROUPNAME | NAME |  AGE
DOG       | DOG1 |  10
          | DOG2 |  12
          | DOG3 |  14
CAT       | CAT1 |  16
          | CAT2 |  18

QUERY EXPLANATION

The innerQuery (i) is for Ranking and getting the rownumbers based on the first 3 characters of the animal name. Using case statement to display the animal name only if rownumber=1. A blank character would be displayed if rownumber is anything else other than 1.

You can group this using SUBSTR()

select SUBSTR(name,1,3) as n from test group by n;

DEMO

Result you want:

select SUBSTR(name,1,3) as n,id,name,age from test;

DEMO

SELECT SUBSTRING(name,1,3) AS first3Char, name,age FROM test2
GROUP BY first3Char,fName,lName

Please check if above Query would serve your purpose.