字符型
 ASCII
 CHR
 LOWER
 UPPER
 INITCAP
 CONCAT
 SUBSTR
 LENGTH
 INSTR
 TRIM
 dump
 lpad
 rpad
 REPLACE
 
ASCII('字符')
 返回字符的ASCII码值
idle> select ASCII('a') from dual;
ASCII('A')
----------
 97

idle> select ASCII('A') from dual;

ASCII('A')
----------
 65

idle>

CHR('n')
 返回n的字符值 n是ASCII码数
idle> select chr(65) from dual;

C
-
A

idle> select chr(39) from dual;

C
-
'

idle>

但是求单引号的ASCII码写法很特殊 两个单引带表一个单引

idle> select ASCII(''') from dual;
ERROR:
ORA-01756: quoted string not properly terminated

idle> select ASCII('''') from dual;

ASCII('''')
-----------
  39

idle>

LOWER(列名|表达式)
小写转换
idle> select lower('ABC') from dual;

LOW
---
abc

idle>
dual 为虚表,当一个语句不需要从表中获取数据时,但又要维持SQL语法,Oracle才提供了虚表来解决这个问题

UPPER(列名|表达式)
大写转换

idle> select upper('abc') from dual;

UPP
---
ABC

idle>

INITCAP(列名|表达式)
每个词的词头大写 其他小写

idle> select initcap('abC dEf XYZ') from dual;

INITCAP('AB
-----------
Abc Def Xyz

idle>

CONCAT(列名|表达式,列名|表达式)
将第一个字符串和第二个字符串连接

idle> select concat('abc','xyz') from dual;

CONCAT
------
abcxyz

不太常用,因为我们可以用 || 连接
idle> select 'abc'||'xyz' from dual;

'ABC'|
------
abcxyz

idle>

SUBSTR(列名|表达式,m,[n])
返回指定子串,该子串是从第m个字符开始,其长度为n,不指定n值则从m到最后

idle> select substr('abcdefxyz',4,3) from dual;

SUB
---
def

idle> select substr('abcdefxyz',4) from dual;

SUBSTR
------
defxyz

idle>

LENGTH(列名|表达式)
返回字符串的长度
idle> select length('abcdefxyz') from dual;

LENGTH('ABCDEFXYZ')
-------------------
    9

idle>

INSTR (列名|表达式,'字符串',[m],[n])
从表达式或列中搜索给定的字符串的所处位置,m代表从第几个开始搜,n代表第几次出现. m和n默认都是1

idle> select INSTR('abcdddxyz','d') from dual;

INSTR('ABCDDDXYZ','D')
----------------------
       4

idle>
idle> select INSTR('abcdddxyz','d',5) from dual;

INSTR('ABCDDDXYZ','D',5)
------------------------
         5

idle> select INSTR('abcdddxyz','d',5,2) from dual;

INSTR('ABCDDDXYZ','D',5,2)
--------------------------
    6

idle>

TRIM([leading|]trailing|both 要去掉的字符 FROM 源字符串)
从源字符串中去掉指定的字符 可以用leading tailing来修饰去掉的字符串是在开头或结尾,默认是两者都  默认截取的是空格

idle> select trim('a' from 'aaabcdeaaafxyzaaa') from dual;

TRIM('A'FRO
-----------
bcdeaaafxyz

idle> select trim(leading 'a' from 'aaabcdeaaafxyzaaa') from dual;

TRIM(LEADING'A
--------------
bcdeaaafxyzaaa

idle> select trim(trailing 'a' from 'aaabcdeaaafxyzaaa') from dual;

TRIM(TRAILING'
--------------
aaabcdeaaafxyz

idle>

左补齐lpad 右补齐rpad
将不足20个字符的位置用指定符号填充.
idle> select lpad(ename,20,'-') ,rpad(ename,20,'-') from emp where ename like 'S%';

LPAD(ENAME,20,'-')   RPAD(ENAME,20,'-')
-------------------- --------------------
---------------SMITH SMITH---------------
---------------SCOTT SCOTT---------------
idle>

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