This function creates a valid SQL statement based on the specified variable, operator, and values. It handles different operators such as "greater", "less", "equal", and "between".
make_valid_sql(conn, variable, operator, values)A character string representing the valid SQL statement.
The connection object or database connection string.
The variable for which the SQL statement is created.
The operator to be used in the SQL statement.
The values to be used in the SQL statement.