1、判斷字符串為空串

--Mysql：在MySQL中，空值(Null)與空字符(’’)是不相同的

select '' is null;

+------------+

| '' is null |

+------------+

| 0 |

+------------+

select trim(' ')='';

+--------------+

| trim(' ')='' |

+--------------+

| 1 |

+--------------+

--所以在mysql中可以這樣來判斷空串

select *

from table

where trim(col) = '';

--***************************

--而在oracle，則空值(Null)與空字符(’’)是一樣的

select *

from table

where trim(col) is null;

2、虛表dual，oracle和mysql均存在該虛表，但對于下面語句：

select * from dual;

-- mysql執行會報錯

--oracle執行會查出如下：

D

-

X

3、關聯表進行刪除

-- mysql

delete a from hs_sett.fusettleholdsinfo a, hs_sett.fusettarg b

where a.exchange_type = b.exchange_type

and b.exchange_type = 'F1';

--oracle

delete from hs_futuvip.fusettleholdsinfo a

where exists(select 1

from hs_futuvip.fusettarg b

where a.futu_exch_type = b.futu_exch_type

and b.futu_exch_type = 'F1');

4、關聯表更新

-- mysql

update futransfertotal a, fusettarg b

set a.clear_balance=0,a.active_flag='1'

where a.exchange_type = b.exchange_type

and b.asset_kind = '1';

-- oralce

update futransfertotal a

set a.clear_balance=0,a.active_flag='1'

where exists(select 1

from fusettarg b

where a.futu_exch_type = b.futu_exch_type

and b.futu_exch_type = 'F1')

總結

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