oracle中函数分为:字符类函数、数类函数、日期类函数、空处理函数、转换类函数、其他常用函数 这次主要整理几个ORACLE中常用到的SQL函数 如下: lower()函数 内容转换小写 SQL SELECT LOWER(T_NAME) FROM test_partitioning2; LOWER(T_NAME) ------------
oracle中函数分为:字符类函数、数值类函数、日期类函数、空值处理函数、转换类函数、其他常用函数
这次主要整理几个ORACLE中常用到的SQL函数 如下:
lower()函数 内容转换小写
SQL> SELECT LOWER(T_NAME) FROM test_partitioning2;
LOWER(T_NAME)
-------------
a
b
c
d
e
e
e
7 rows selected
upper()函数 内容抓换大写
SQL> SELECT UPPER(T_NAME) FROM test_partitioning2;
UPPER(T_NAME)
-------------
A
B
C
D
E
E
E
7 rows selected
ltrim()去除左右空格(前后各两空格)
SQL> select length(ltrim(' oracle ')),length(ltrim(' oracle ',' ')) from dual;
LENGTH(LTRIM('ORACLE')) LENGTH(LTRIM('ORACLE',''))
----------------------- --------------------------
8 8
--ltrim中第二个参数没有指定参数,默认删除' '空格的字符,即与ltrim(' oracle ',' ')效果相同;
ltrim删除字符串中指定字符
SQL> select ltrim('oracle','roc'),ltrim('lllearner','ale') from dual;
LTRIM('ORACLE','ROC') LTRIM('LLLEARNER','ALE')
--------------------- ------------------------
acle rner
--ltrim函数第二个参数不是以‘roc’作为整体删除的,而是以单个字符删除。碰到连续的字符将连续删除。
rtrim()去除左右空格(前后各两空格)
SQL> select length(rtrim(' oracle ')),length(rtrim(' oracle ',' ')) from dual;
LENGTH(RTRIM('ORACLE')) LENGTH(RTRIM('ORACLE',''))
----------------------- --------------------------
8 8
SQL> select rtrim('oracle','e'),rtrim('learner','rle') from dual;
RTRIM('ORACLE','E') RTRIM('LEARNER','RLE')
------------------- ----------------------
oracl learn
--作用同ltrim函数一样,只不过这是从右边往左边检索删除
trim()函数包括了ltrim()、rtrim()函数功能
语法:TRIM([LEADING | TRAILING| BOTH] [trim_char_from] 列明或表达式)
LEADING:表示从左边删除
TRAILING:右边删除
BOTH:两边同时删除(默认)
例子:
SQL> SELECT TRIM(LEADING '*' FROM '**oracle*') c1,TRIM(TRAILING '*' FROM '**oracle*') c2,TRIM(BOTH '*' FROM '**oracle*') c3,
2 TRIM('*' FROM '**oracle*') c4,LENGTH(TRIM(' oracle')) c5 from dual
3 ;
C1 C2 C3 C4 C5
------- -------- ------ ------ ----------
oracle* **oracle oracle oracle 6
length()与lengthb() 函数
两者都是返回长度,前者返回字符串长度,后者返回字节长度
SQL> select length('数据库'),lengthb('数据库') from dual;
LENGTH('数据库') LENGTHB('数据库')
---------------- -----------------
3 9
substr()与substrb() 函数
两个都是返回字符串的字串,后者按照字符返回
SQL> select substr('oracle',1,3) c1,substr('oracle',1,3) c2,substr('学习数据库',1,3) c3,substrb('学习数据库',1,3) from dual;
C1 C2 C3 SUBSTRB('学习数据库',1,3)
--- --- --------- -------------------------
ora ora 学习数 学
round()函数
功能将列明所表示的数值进行四舍五入,语法格式
ROUND(列明,X) X表示保留几个小数,不写默认为0,小数点后面四舍五入
例子:
SQL> select round(123.456) from dual;
--------------
123
SQL> select round(123.456) from dual;
ROUND(123.456)
--------------
123
--round()函数还可以对日期类型数据进行处理
TRUNC()函数
功能:将列名所表示的数值进行截取,语法如下:
TRUNC(列名,x) x表示截取到小数点的第几位(不进行四舍五入),默认为0,如果x为负数,则表示从小数点左边第x位截取
SQL> select trunc(123456.78) from dual;
TRUNC(123456.78)
----------------
123456
SQL> select trunc(123456.78,1) from dual;
TRUNC(123456.78,1)
------------------
123456.7
--trunc第二个参数为负数,表示从小数点左边截断,截断几位自动补0。 如下:
SQL> select trunc(1234.567,-1) A,trunc(123456.789,-2) B,trunc(3456332.1,-4) C from dual;
A B C
---------- ---------- ----------
1230 123400 3450000
--trunc函数也还可以对日期类型数据进行处理
--trunc与round不同,round是小数点后面进行四舍五入,而trunc直接截断,这是两函数区别。
last_day()函数
功能:获取当前日期所在月的最后一天
SQL> select sysdate,last_day(sysdate) last_day from dual;
SYSDATE LAST_DAY
----------- -----------
2013/10/20 2013/10/31
NVL()函数
功能:实现空值转换,根据一个表达式的值是否为空来判断返回相应列明或表达式。主要用于对空值进行处理,语法如下:
NVL(列名或表达式,列名或表达式)
如果第一个参数值返回空值,则返回第二个参数值,否则返回第一个参数值,第一第二参数值都可为任意类型值,但两个参数类型必须相同。
NVL2()函数NVL()函数扩展函数
功能也是对一个空值转换函数,如果第一个参数值不为空,则返回第二个参数值,否则返回第三个参数值。第一个参数可以为任意类型,
第二第三参数除LONG类型以外的任何类型。语法如下:
NVL2(列名或表达式,列名或表达式,列名或表达式)
TO_CHAR()函数
功能:将非字符数据转换为字符型数据,并设置字符的输出格式,语法如下:
TO_CHAR(列名或表达式,[格式],[NLS参数])
第一个参数:要指定转换列名
第二个参数:转换列名指定转换格式
第三个参数:显示格式国家语言支持参数,如不设置则使用默认NLS参数指定
SQL> SELECT TO_CHAR(1234567,'9,999,999') C1,TO_CHAR(123.456,'9999,9999') C2,TO_CHAR(12.466666,'9.99') C5 from dual;
C1 C2 C5
---------- ---------- -----
1,234,567 123 #####
#####:表示当整数部分的长度大于格式字符串中指定的长度时,则返回一个由#组成字符串
SQL> select to_char(systimestamp,'YYYY-MM-DD hh24:MI:SS') d1, to_char(systimestamp,'WW') d2,to_char(sysdate,'W') d3 from dual;
D1 D2 D3
------------------- -- --
2013-10-20 20:56:58 42 3
TO_DATE(函数
功能:将字符型数据转换成日期型数据,并设置日期的输出格式,语法如下:
TO_CHAR(列名或表达式,[格式]),[NLS参数]
第一个参数:转换列名
第二个参数:指定转换后显示格式
第三个参数:显示格式国家语言支持参数,如不设置则使用默认NLS参数指定
SQL> select to_char(to_date('2013-10-20','yyyy-mm-dd'),'DAY') from dual;
TO_CHAR(TO_DATE('2013-10-20','
------------------------------
星期日
DECODE() 函数
功能:类似与高级语言中IF ELSE的分支语句
SELECT T_ID,T_NAME,T_RESEARCH,DECODE(T_TITLEID,1,'教授',2,'副教授',3,'其他') from dual;

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