在oracle 9i之前,對中文的排序税迷，是默認按2進制編碼來進行排序的. 9i時增加了幾種新的選擇:
按中文拼音進行排序:SCHINESE_PINYIN_M
按中文部首進行排序:SCHINESE_RADICAL_M
按中文筆畫進行排序:SCHINESE_STROKE_M
而oracle 9i是對中文的排序是默認按拼音排序(并不是指NLS_SORT = SCHINESE_PINYIN_M,而是說SQL中不指定NLS_SORT時對中文列排序時默認按拼音)的睡扬，跟之前的2進制編碼排序有所不同.具體用法如下:
直接寫在sql中,例如:
SELECT * FROM TEAM ORDER BY NLSSORT(排序字段名,'NLS_SORT = SCHINESE_PINYIN_M');
SELECT * FROM TEAM ORDER BY NLSSORT(排序字段名,'NLS_SORT = SCHINESE_STROKE_M');
SELECT * FROM TEAM ORDER BY NLSSORT(排序字段名,'NLS_SORT = SCHINESE_RADICAL_M');
配置在初始化參數(shù)NLS_SORT中,這可以在數(shù)據(jù)庫創(chuàng)建時指定,也可以通過alter session來修改.如果是前者廊蜒，則在所有session中生效.例如:
使用 select * from NLS_SESSION_PARAMETERS;語句可以看到NLS_SORT的值.
更改配置文件: alter system set nls_sort='SCHINESE_PINYIN_M' scope=spfile;
更改 session:alter SESSION set NLS_SORT = SCHINESE_PINYIN_M;
這里要額外注意一下性能問題,按oracle官方文檔的解釋,oracle在對中文列建立索引時,是按照2進制編碼進行排序的,所以如果NLS_SORT被設(shè)置為BINARY時扒俯，排序則可以利用索引.如果不是2進制排序友酱，而是使用上面介紹的3種針對中文的特殊排序烤低，則oracle無法使用索引兼丰，會進行全表掃描.這點一定要注意,多用plsql工具比較一下執(zhí)行效率.解決方法是,在此列上建立linguistic index.例如:CREATE INDEX nls_index ON my_table (NLSSORT(name, 'NLS_SORT = SCHINESE_PINYIN_M'));
以下是oracle文檔中的原文:
Note:
Setting NLS_SORT to anything other than BINARY causes a sort to use a full table scan, regardless of the path chosen by the optimizer. BINARY is the exception because indexes are built according to a binary order of keys. Thus the optimizer can use an index to satisfy the ORDER BY clause when NLS_SORT is set to BINARY. If NLS_SORT is set to any linguistic sort, the optimizer must include a full table scan and a full sort in the execution plan.