Use this:
SUSBSTR(table.column_name,1,instr(table.column_name,',',1,1)-1)
It creates a substring from the first character to the character before the first comma in the field
Use this:
SUSBSTR(table.column_name,1,instr(table.column_name,',',1,1)-1)
It creates a substring from the first character to the character before the first comma in the field