oracle 开发 第4章 函数

--获得字符x的ASCII码
select
ascii(‘a‘),ascii(‘A‘),ascii(‘z‘),ascii(0),ascii(9)
from dual;            

--获得ASCII码为x的字符
select
chr(97),chr(65),chr(122),chr(48),chr(57)
from dual;

--将y添加到x之后
--concat()和||操作符功能相同，||可以连接多个字符串，concat()只能连接2个字符串
select concat(first_name,last_name)
from customers;

--将x中每个单词的首字母转换成大写
select product_id,initcap(description)
from products
where product_id < 4;

--在x中查找find_string，返回find_string所在位置
--start开始查找的位置
--occurrence第几次出现的位置
select name,instr(name,‘Science‘)
from products
where product_id = 1;

select name,instr(name,‘e‘,1,2)
from products
where product_id = 1;

select name,instr(name,‘e‘,-1,3)
from products
where product_id = 1;

select customer_id,dob,instr(dob,‘JAN‘)
from customers
where customer_id = 1;

--获得x中字符的个数
select name,length(name)
from products;

select price,length(price)
from products
where product_id < 3;

--LOWER(x)将x中的字母转换成小写
--UPPER(x)将x中的字母转换成大写
select upper(first_name),lower(last_name)
from customers;

--LPAD在x的左边补齐空格，使x的总长度达到width个字符
--RPAD在x的右边补齐空格，使x的总长度达到width个字符
select rpad(name,30,‘.‘),lpad(price,8,‘*+‘)
from products
where product_id < 4;

--LTRIM从x的左边截去字符
--RTRIM从x的右边截去字符
--TRIM从x的左、右各截去字符
select
ltrim(‘ Hello Kathy Lindsey! ‘),
rtrim(‘ Hi Doreeen Oakley!abcabc‘, ‘abc‘),
trim(‘0‘ from ‘000Hey Steve Button!00000‘)
from dual;

--x为空，返回value，否则返回x
select customer_id,nvl(phone,‘Unknown Phone Number‘)
from customers;

--x非空，返回value1;否则返回value2
select customer_id,nvl2(phone,‘Known‘,‘Unknown‘)
from customers;

--在x中查找search_string，并将其替换为replace_string
select replace(name,‘Science‘,‘PHYSICS‘)
from products
where product_id = 1;

--获得包含x发音的字符串，用于对英文拼写不同发音相似的单词进行比较
select last_name
from customers
where soundex(last_name) = soundex(‘whyte‘);

select last_name
from customers
where soundex(last_name) = soundex(‘bloo‘);

--从x中获得,从start位置开始的,长度为length的子字符串
select substr(name,2,7)
from products
where product_id < 4;

select substr(name,-5,3)
from products
where product_id < 4;

select substr(‘Mary had a little lamb‘,12,6) from dual;

select name,upper(substr(name,2,8))
from products
where product_id < 4;

--返回x的绝对值
select abs(10),abs(-10) from dual;

select product_id,price,price - 30,abs(price - 30)
from products
where product_id < 4;

--返回大于、等于x的最小整数(上取整)
select ceil(5.8),ceil(-5.2) from dual;

--返回小于、等于x的最大整数(下取整)
select floor(5.8),floor(-5.2) from dual;

--返回一组values中的最大值
select greatest(3,4,1) from dual;
select greatest(50/2,exp(2)) from dual;

--返回一组values中的最小值
select least(3,4,1) from dual;
select least(50/2,exp(2)) from dual;

--返回x的y次幂
select power(2,1),power(2,3) from dual;

--返回x的四舍五入值,精确到小数点后y位
select round(5.75),round(5.75,1),round(5.75,-1) from dual;

--x为正,返回1;x为0,返回0;x为负,返回-1
select sign(-5),sign(5),sign(0) from dual;

--返回x的平方根
select sqrt(25),sqrt(5) from dual;

--返回x在小数点后y位的截断值
select trunc(5.75),trunc(5.75,1),trunc(5.75,-1) from dual;

--将x转换为ASCII字符串
select asciistr(‘ABC D CDE‘) from dual;
select asciistr(chr(128) || ‘ ‘ || chr(129)||‘ ‘|| chr(130)) from dual;

--将二进制数x转换为NUMBER类型
select bin_to_num(1,0,1),bin_to_num(1,1,0),bin_to_num(1,1,1,0) from dual;

--将x转换为由type指定的兼容数据库类型
select
    cast(12345.67 as varchar2(10)),
    cast(‘9A4F‘ as raw(2)),
    cast(‘05-JUL-07‘ as date),
    cast(12345.678 as number(10,2))
from dual;

select
    cast(price as varchar2(10)),
    cast(price +2 as number(7,2)),
    cast(price as binary_double)
from products
where product_id = 1;

--将x转换为rowid
select rowid from customers where customer_id = 1;
select * from customers where rowid = chartorowid(‘AAAWf4AAEAAAAHjAAA‘);

--将x转换为Unicode字符串
select
    compose(‘o‘||unistr(‘\0308‘)),
    compose(‘e‘||unistr(‘\0302‘))
from dual;

--将x从source_char_set指定的字符集转换为dest_char_set指定的字符集
select convert(‘A B C‘,‘US7ASCII‘,‘WE8ISO8859P1‘) from dual;

--先对x进行分解，再将其转换为Unicode字符串
select decompose(‘oe‘) from dual;

--将包含16进制数字的字符串x转换为二进制数(RAW)
select utl_raw.cast_to_varchar2(hextoraw(‘41414743‘)) from dual;

--将RAW二进制数x转换为16进制数的VARCHAR2字符串
select rawtohex(41414743) from dual;

--将ROWID x转换为VARCHAR2字符串
select rowid,customer_id,first_name,last_name
from customers
where rowidtochar(rowid) like ‘%KAAA‘;

--将x转换为BINARY_DOUBLE
select to_binary_double(1087623) from dual;

select to_binary_float(10623) from dual;

--将x中单字节字符转换为对应的多字节字符
select to_multi_byte(‘A‘) from dual;

--将x转换为数字
select to_number(‘970.13‘) from dual;
select to_number(‘970.13‘) + 25.5 from dual;
select to_number(‘-$12,345.67‘,‘$99,999.99‘) from dual;

--将x中多字节字符转换为对应的单字节字符
select to_single_byte(‘A‘) from dual;

--在x中查找pattern
select customer_id,first_name,last_name,dob
from customers
where regexp_like(to_char(dob,‘YYYY‘),‘^196[5-8]$‘);

select customer_id,first_name,last_name,dob
from customers
where regexp_like(first_name,‘^j‘,‘i‘);

--在x中查找pattern，并返回pattern所在的位置
select
    regexp_instr(‘But, soft! What light through yonder window breaks?‘,
        ‘l[[:alpha:]]{4}‘) as result
from dual;

select 
    regexp_instr(‘But, soft! What light through yonder window softly breaks?‘,
        ‘s[[:alpha:]]{3}‘, 1, 2) as result
from dual;

select 
    regexp_instr(‘But, soft! What light through yonder window breaks?‘,
        ‘o‘, 10, 2) as result
from dual;

--在x中查找pattern，并将其替换为replace_string
select
    regexp_replace(‘But, soft! What light through yonder window breaks?‘,
        ‘l[[:alpha:]]{4}‘,‘sound‘) as result
from dual;

--在x中查找pattern的子字符串
select
    regexp_substr(‘But, soft! What light through yonder window breaks?‘,
        ‘l[[:alpha:]]{4}‘) as result
from dual;

--返回pattern在x中出现的次数
select
    regexp_count(‘But, soft! What light through yonder window softly breaks?‘,
        ‘s[[:alpha:]]{3}‘) as result
from dual;

--返回x的平均值
select avg(price) from products;
select avg(price + 2) from products;
select avg(distinct price) from products;

--返回包含x的查询的行数
select count(product_id) from products;
select count(rowid) from products;

--返回x的最大值、最小值
select max(price),min(price) from products;
select max(name),min(name) from products;
select max(dob),min(dob) from customers;

--返回x的标准差
select stddev(price) from products;

--返回x中所有值的和
select sum(price) from products;

--返回x的方差
select variance(price) from products;

select product_type_id
from products
group by product_type_id;

select product_id,name,price
from products
where product_type_id is null;

select product_id,customer_id
from purchase
group by product_id,customer_id;

select product_type_id,count(rowid)
from products
group by product_type_id
order by product_type_id;

select product_type_id,avg(price)
from products
group by product_type_id
order by product_type_id;

select product_type_id,variance(price)
from products
group by product_type_id
order by product_type_id;

select variance(price)
from products
group by product_type_id
order by product_type_id;

select variance(price)
from products
group by product_type_id
order by variance(price);

--先用WHERE子句对返回的行进行过滤，再用GROUP BY子句对保留的行进行分组
select product_type_id,avg(price)
from products
where price < 15
group by product_type_id
order by product_type_id;

--先用WHERE子句对返回的行进行过滤，在用GROUP BY子句对保留的行进行分组，最后HAVING子句对行组进行过滤
select product_type_id,avg(price)
from products
where price < 15
group by product_type_id
having avg(price) > 13
order by product_type_id;

select product_type_id,avg(price)
from products
where price < 15
group by product_type_id
having avg(price) > 13
order by avg(price);