PgSQL converts string to double type (to_number())

Today I write sql When , Find out PG There is a table in which the area field is set to string type , In this way, statistics cannot be used sum Function , So you need to convert the string to double Add the types .

select sum(to_number(mj,9999.99)) as amountmj from table group by area

among 9999.99 It doesn't matter mj The value of the field is still amountmj The value of cannot exceed 9999.99, And keep two decimal places .