Oracle中的双引号的作用，建表时加双引号，会保留表名的大小写写入数据库，双引号没有写进数据库，而select时oracle会默认转成大
1.建表时加双引号，会保留表名的大小写写入数据库，
注意: 双引号没有写进数据库，而select时Oracle会默认转成大写去数据字典中查找，当然找不到啦
sys@ziling> conn scott/scott
2.双引号用在字符串中当成普通字符处理，且不一定要成对出现。
3.双引号用在to_char函数里的字符串中时，有特殊作用，，可以将特殊字符包起来，避免出现ORA-01821: date format not recognized错误。也就是说，去掉双引号和其包含的字符后，剩下的应该是一个合法的格式串。
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