SQL 归来 - 爱码网

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	タイムゾーン情報あり	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

SQL 归来

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
*/

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