Oracle的转义字符
对于Oracle的转义字符，对然了解，但是一直不是很明白。而且在SQLPlus下的ESCAPE还和函数ESCAPE不是一个意思，更加容易搞混，所以专门来学习一下。首先可以通过几个简单的例子来了解一下这个函数在SQL中的用法。
SQL> create table t_char(a varchar2(20));
SQL> insert into t_char values('a_b');
SQL> insert into t_char values('acb');
SQL> insert into t_char values('a%b');
SQL> insert into t_char values('a''b');
SQL> insert into t_char values('a/b');
SQL> insert into t_char values('a\b');
SQL> insert into t_char values('%');
SQL> insert into t_char values('_');
SQL> insert into t_char values('a');
SQL> commit;
SQL> select * from t_char;
A
--------------------
a_b
acb
a%b
a'b
a/b
a\b
%
_
a
SQL> select * from t_char where a like 'a_b';
A
--------------------
a_b
acb
a%b
a'b
a/b
a\b
SQL> select * from t_char where a like 'a\_b' escape '\';
A
--------------------
a_b
--可见要查询含有通配字符的字符串，必须要使用escape函数
SQL> select * from t_char where a like 'a\'b' escape '\';
ERROR:
ORA-01756: quoted string not properly terminated
SQL> select * from t_char where a like 'a''b' escape '\';
A
--------------------
a'b
--但是字符'还是需要用两个''来代替字符串中的单引号
SQL> select * from t_char where a like 'ax_b' escape 'x';
A
--------------------
a_b
SQL> select * from t_char where a like 'a''_b' escape '''';
A
--------------------
a_b
SQL> select * from t_char where a like 'a_%b' escape '_';
A
--------------------
a%b
--可以用其他字符，甚至是“'”、“_”、“%”来用作转义字符，但是一般都使用\，以免发生逻辑错误
SQL> select * from t_char where a like 'a\/b' escape '\';
select * from t_char where a like 'a\/b' escape '\'
*
ERROR at line 1:
ORA-01424: missing or illegal character following the escape character
SQL> select * from t_char where a like 'a_/b' escape '_';
select * from t_char where a like 'a_/b' escape '_'
*
ERROR at line 1:
ORA-01424: missing or illegal character following the escape character
SQL> select * from t_char where a like 'a//b' escape '/';
A
--------------------
a/b
SQL> select * from t_char where a like 'a/\b' escape '/';
select * from t_char where a like 'a/\b' escape '/'
*
ERROR at line 1:
ORA-01424: missing or illegal character following the escape character
SQL> select * from t_char where a like 'a\\b' escape '\';
A
--------------------
a\b
--要搜索"/"或者"\"则必须使用与之相同的符号作为转义字符，否则无效
--基本上的使用方法就是这些了，最后再强调一下：这里的escape函数，和sqlplus中的escape环境参数·毫·无·关·系·
SQL> show escape
escape OFF