TO_DATE cũng là một chức năng chuyển đổi. Phải mất một chuỗi ký tự hoặc một số và chuyển nó thành kiểu dữ liệu DATE. Sau đó nó có thể được sử dụng trong số học ngày để tính toán MONTHS_BETWEEN, NEXT_DAY, và các chức năng ngày khác. Mặc dù có chức năng chuyển đổi được liệt kê trong Bảng 10-1, phổ biến nhất được sử dụng là | 402 Part II SQL and SQL Plus Within the into table clause you can use the recnum keyword to assign a record number to each logical record as it is read from the datafile and that value will be inserted into the assigned column of the table. The constant keyword allows you to assign a constant value to a column during the load. For character columns enclose the constant value within single quotes. If you use the sysdate keyword the selected column will be populated with the current system date and time. I CheckOutDate SYSDATE If you use the sequence option SQL Loader will maintain a sequence of values during the load. As records are processed the sequence value will be increased by the increment you specify. If the rows fail during insert and are sent to the bad file those sequence values will not be reused. If you use the max keyword within the sequence option the sequence values will use the current maximum value of the column as the starting point for the sequence. The following listing shows the use of the sequence option I Seqnum_col SEQUENCE MAX 1 You can also specify the starting value and increment for a sequence to use when inserting. The following example inserts values starting with a value of 100 incrementing by 2. If a row is rejected during the insert its sequence value is skipped. t Seqnum_col SEQUENCE 100 2 If you store numbers in VARCHAR2 columns avoid using the sequence option for those columns. For example if your table already contains the values 1 through 10 in a VARCHAR2 column then the maximum value within that column is 9 the greatest character string. Using that as the basis for a sequence option will cause SQL Loader to attempt to insert a record using 10 as the newly created value and that may conflict with the existing record. SQL Loader control files can support complex logic and business rules. For example your input data for a column holding monetary values may have an implied decimal 9990 would be inserted as . In SQL Loader you
