extrar cantidad de registros diferentes

[Libras]

Para mostrar 5 de cada grupo deberias de hacer algo como esto:

Código MySQL:

create table tabla
(
correo varchar(300)
);
 
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
insert into tabla values ('[email protected]');
 
 
 
SELECT
        completo,n as row_number,  correo
    FROM
      ( SELECT  @prev := '', @n := 0 ) init
    JOIN
      (         
      SELECT  @n := if(completo != @prev, 1, @n + 1) AS n,
                @prev := completo,
                completo, correo
            FROM  (
                        SELECT  completo, correo FROM(
                        SELECT SUBSTRING(correo1,1,INSTR(correo1,'.')-1) AS completo, correo FROM(
                        SELECT SUBSTRING(correo, INSTR(correo,'@')+1, length(correo)) AS correo1, correo FROM tabla
                        ) AS t1
                        ) AS t2 
                        #WHERE completo<>'outlook'
            ) as t3
            ORDER BY
                completo   ASC          
      ) x
    WHERE  n <= 5
    ORDER BY  completo, n;
 

Resultado:

aja 1 [email protected]
aja 2 [email protected]
otro 1 [email protected]
otro 2 [email protected]
outlook 1 [email protected]
outlook 2 [email protected]
outlook 3 [email protected]
tu 1 [email protected]
tu 2 [email protected]
tu 3 [email protected]
yo 1 [email protected]
yo 2 [email protected]
yo 3 [email protected]
yo 4 [email protected]
yo 5 [email protected]

Si ves el dominio "yo" tiene mas de 5 registros y solo muestra 5 en el query