Oracle的order by 使用小結

ORDER BY 是用來對select結果排序的，很簡單，但是也總結一下吧。

1. 按列名排序，預設是升序的。
單列升序：select<column_name> from <table_name> order by <column_name>;
單列降序：select <column_name> from table_name order by <column_name> desc;
多列升序：select <column_one>, <column_two> from table_name order by <column_one>, <column_two>;
多列降序：select <column_one>, <column_two> from <table_name> order by <column_one> desc, <column_two> desc;
多列混合降序：select column_one, column_two from table_name order by column_one desc, column_two desc;

2. 按列的位序排序, 預設是升序
select * from <table_name> order by 1

3. NULL排序
空值在前：select <column_name> from <table_name> order by <column_name> NULLS FIRST;
空值在後：select <column_name> from <table_name> order by <column_name> NULLS LAST;