1.大小写转换

initcap(char) 把每个字符串的首字符换成大写

upper(char) 整个字符串转换成大写

BYS@bys1>Select lower(ename),upper(ename),initcap(ename) from emp where rownum<3;
LOWER(ENAM UPPER(ENAM INITCAP(EN
---------- ---------- ----------
smith      SMITH      Smith
allen      ALLEN      Allen

2.字符连接CONCAT和||

CONCAT (char1, char2)    连接char1和char2，注意：CONCAT只能连接两个字符串，连接三个将报错。

BYS@bys1>select ename,job,ename,concat(ename,job) from emp where rownum<3;
ENAME      JOB       ENAME      CONCAT(ENAME,JOB)
---------- --------- ---------- -------------------
SMITH      CLERK     SMITH      SMITHCLERK
ALLEN      SALESMAN  ALLEN      ALLENSALESMAN
BYS@bys1>select ename,job,ename,concat(ename,job,ename) from emp where rownum<3;
select ename,job,ename,concat(ename,job,ename) from emp where rownum<3
                       *
ERROR at line 1:
ORA-00909: invalid number of arguments

||连接符，一大优势是可以在连续符中间添加指定的字符

BYS@bys1>select ename,job,ename,ename||ename||job from emp where rownum<3;
ENAME      JOB       ENAME      ENAME||ENAME||JOB
---------- --------- ---------- -----------------------------
SMITH      CLERK     SMITH      SMITHSMITHCLERK
ALLEN      SALESMAN  ALLEN      ALLENALLENSALESMAN

BYS@bys1>select ename,job,ename,'mingzi '||ename||ename||'  gongzuo  '||job from emp where rownum<3;
ENAME      JOB       ENAME      'MINGZI'||ENAME||ENAME||'GONGZUO'||JOB
---------- --------- ---------- -----------------------------------------------
SMITH      CLERK     SMITH      mingzi SMITHSMITH  gongzuo CLERK
ALLEN      SALESMAN  ALLEN      mingzi ALLENALLEN  gongzuo  SALESMAN

3.求字符串的长度;length  字符串要单引

 length--按照字,可以求字符串长度，也可以求数字的长度

 lengthb--按字节

 lengthc--unicode的长度

BYS@bys1>select ename,length(ename),sal,length(sal) from emp where rownum<5;
ENAME      LENGTH(ENAME)        SAL LENGTH(SAL)
---------- ------------- ---------- -----------
SMITH                  5        800           3
ALLEN