What will be the output of

Select

CONCAT(
REPLICATE(STUFF('12345678ABC',1,Patindex('%[a|b|c|d]%',REVERSE(REVERSE('12345678ABC')))-1,''),5)
,
STUFF('12345678ABC',1,Patindex('%[a|b|c|d]%',REVERSE(REVERSE('12345678ABC')))-1,'')
) ?

THE REPLICATE(STUFF('12345678ABC',1,Patindex('%[a|b|c|d]%',REVERSE(REVERSE('12345678ABC')))-1,''),5) will return 'ABCABCABCABCABCABC' and STUFF('12345678ABC',1,Patindex('%[a|b|c|d]%',REVERSE(REVERSE('12345678ABC')))-1,'') will return ABC. Concat function will merge them.