SQL 归来

1. PL/SQL 转义

• select order#, ………  from ****
• select col1 from A where col2 like '%\_keywors%' escape '\';
• update A set url = 'homepage.aspx?code=32' ||  '&' || 'active=0'     --&

update A set url = 'homepage.aspx?code=32' ||  chr(38) || 'active=0'     --&

2. EXTRACT

日付の要素		element 引数
年		YEAR
月		MONTH
日		DAY
時		HOUR
分		MINUTE
秒		SECOND
時	タイムゾーン 情報あり	TIMEZONE_HOUR
分		TIMEZONE_MINUTE
タイムゾーン名称		TIMEZONE_REGION
タイムゾーン略称		TIMEZONE_ABBR

SELECT EXTRACT(YEAR FROM SYSDATE) FROM DUAL

3.    TRUNC

SELECT SYSDATE S1,                    
     TRUNC(SYSDATE) S2,                 --返回当前日期,无时分秒
     TRUNC(SYSDATE,'YEAR') YEAR,        --返回当前年的1月1日,无时分秒
     TRUNC(SYSDATE,'MONTH') MONTH ,     --返回当前月的1日,无时分秒
     TRUNC(SYSDATE,'DAY') DAY           --返回当前星期的星期天,无时分秒
   FROM DUAL

S1	S2	YEAR	MONTH	DAY
2015/3/11   11:30	2015/3/11	2015/1/1	2015/3/1	2015/3/8

4.  调用存储过程

DECLARE
  MY_STR_DATE VARCHAR2(100);
BEGIN
  MY_STR_DATE := 'ASDFASDFASDF';
  DBMS_OUTPUT.put_line(MY_STR_DATE);
END;

5.  Exists -- 替换 minus 和 intersect

select *
  from (select 1 col1, 'a' col2
          from dual
        union all
        select 2 col1, 'b' col2
          from dual) t
 where not exists (select 'x'
          from (select 1 col1, 'a' col2
                  from dual
                union all
                select 2 col1, 'b' col2
                  from dual) w
         where t.col1 = w.col1
           and t.col2 = w.col2)

另外： 如果select的内容都出自一个表的时候，比如上面的t和w有不同的列，而最终结果只选择t表中的列，最好用Exists

6. 全角/半角转换（link）

SELECT
TO_MULTI_BYTE(SYS.UTL_I18N.TRANSLITERATE('ｱAあ1１','hwkatakana_fwkatakana')) as full_,
TO_single_BYTE(SYS.UTL_I18N.TRANSLITERATE('アＡあ１１','kana_hwkatakana')) as half
FROM DUAL

FULL_	HALF
アＡあ１１	ｱAｱ11

7. 用A表的数据更新B表的数据

CODE	NAME
1	xxxx
2	yyyy
3	zzzz
4	mmmm
5	wwwww
6	ttttt

CODE	NAME
1	111111
2	222222
3	333333
9	999999

方法1：

update a_code s
   set s.name =
       (select e.name
          from a_data e
         where e.code = s.code
           and rownum < 2)
 where s.code in (select code from a_data);

方法2：

merge into a_code t
     using a_data d
        on (t.code = d.code)  -- 带括号
when matched then
  update
     set t.name = d.name;

CODE	NAME
1	111111
2	222222
3	333333
4	mmmm
5	wwwww
6	ttttt

8. (NOT)  IN / EXISTS

select code from t where code IN (1,2)  => select code from t where code = 1 or code = 2

select code from t where code NOT IN (1,2,null)  => select code from t where code <> 1 and code <> 2 and code <> null

code <> null 的值为unknown，所以NOT IN (1,2,null)的返回的结果集为空，如果用not in就需要把含有null的过滤掉

或则改用Exists

select code from t where NOT EXISTS (select 1 from x where t.code = x.code)

9. coalesce / NVL

coalesce (val1, val2, val3) :

coalesce 可以有多个参数，当val1的值为null的时候，返回val2，如果val2也为空，则返回val3，最后一个参数不能为null即可；如果最后一个参数为null，则返回错误。

NVL(val1, val2) :

NVL只有2个参数，当val1为null的时候，直接返回val2，即使val2为null也不出错；如果val1和val2的数据类型不同，oracle会进行隐式转换，如果转换失败，则返回ERROR；

NVL会同时计算val1和val2的值，对于coalesce只是在val1为null的时候，才会去计算val2的值

另：NVL2(val1, 'completed', 'n/a')

当val1的值为null的时候，返回'n/a'，否则返回'completed'

10. 游标更新  where current of 

 cursor c_f is
    select a,b from f where length(b) = 5 for update;

 open c_f;
  loop
    fetch c_f into v_a, v_b;
    exit when c_f%notfound;
    update f set a=v_a*v_a where current of c_f;
  end loop;

11. Join 写法

select id_num, txt_num, id_lang, txt_lang, txt_trans
  from numbers_en
  join translations using (id_num)
  left join lang using (id_lang);

join translations using id_num 等同于 join translations on numbers_en.id_num = translation.id_num

12. Function VS Procedure: from LINK

13.  赋权限

GRANT SELECT, UPDATE ON "schema1"."table1" TO "schema2" ;

14.  Pipelined Table Functions: LINK

Data is said to be pipelined if it is consumed by a consumer (transformation) as soon as the producer (transformation) produces it, without being staged in tables or a cache before being input to the next transformation.

Pipelining enables a table function to return rows faster and can reduce the memory required to cache a table function's results.

create function
  gen_numbers(n in number default null)
  return array
  PIPELINED
  as
  begin
     for i in 1 .. nvl(n,999999999)
     loop
         pipe row(i);
     end loop;
     return;
  end;
/
-----------------------------------------------------------
/*
select * from TABLE(gen_numbers(3));

 COLUMN_VALUE
 ------------
           1
           2
           3

OR

select *
  from (
  select *
    from (select * from table(gen_numbers(49)))
  order by dbms_random.random
  )
where rownum <= 6
/

 COLUMN_VALUE
 ------------
          47
          42
          40
          15
          48
          23
*/

15. Foreign Key: On delete -> No Action / Cascade / Set null

No Action: prevents deleting a parent when there are children

Cascade: when a referenced parent table row is removed all the child are removed automatically

Set null: set col to null in child when parent table row is removed

16. unicode TO string

'基準日:　' => UNISTR('\57fa\6e96\65e5\003a\3000')

http://unicodelookup.com/   unicode 编码查询

string TO unicode ？？？

17.  频繁插入删除操作，可能导致高水位线，重新分析下表，可能使对表引用的查询更快一点

analyze table XXX compute statistics 

18.  LEFT JOIN :)

1. select count  from  left join B on (A.id = B.id and B.col = 'xxx')
                where 1 =1

2. select count(*) from  left join B on (A.id = B.id) 
                where 1 =1 AND B.col = 'xxx'

1,2 的结果可能会不同，

19.  running total

Table XXX:

select tag, insdate, amount,
       nvl(lag(amount) over(partition by tag order by insdate), 0) lag_total,
       nvl(lead(amount) over(partition by tag order by insdate), 0) 
from xxx

20. check English/digital characters only

[1]

select 1 from dual where  REGEXP_LIKE('ｓｄ巣', '[^ -~]', 'i') union all

select 1 from dual where  REGEXP_LIKE('abc', '[^ -~]', 'i')

[2]

select translate( 'ｓｄ巣abcd', chr(0) || 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789.,- ', chr(0) ) from dual

21. NOCOPY

  TYPE connection IS RECORD (
    host             VARCHAR2(255),       -- Host name of SMTP server
    port             PLS_INTEGER,         -- Port number of SMTP server
    tx_timeout       PLS_INTEGER,         -- Transfer time-out (in seconds)
    private_tcp_con  utl_tcp.connection,  -- For internal use only
    private_state    PLS_INTEGER          -- For internal use only
  );

  FUNCTION helo(c       IN OUT NOCOPY connection,
                domain  IN            VARCHAR2) RETURN reply;

NOCOPY is a IN OUT COPY Which is used avoid the overhad of copying IN OUT Parameter Values.
If IN OUT parameter returns huge records we can specify the NOCOPY to copy the values.
The PLSQL Engine first makes a copy of the record and then during program executing makes a changes to that copy.

22. bitwise operator:BITAND

oracle中只有BITAND函数;

位或：　
BITOR(x,y) = (x + y) - BITAND(x, y);

异或：
BITXOR(x,y) = BITOR(x,y) - BITAND(x,y) = (x + y) - BITAND(x, y) * 2;

应用：赋权，权限判断的时候可以用这个（判断一个角色是否有多个权限）

23. LISTAGG

select listagg(code, ';') within group (order by code) from table_codes

结果：001; 002; 003

24.