各种数据库的比较

1. sql区别以及对应关系。
mysql     oracle      DB2        sqlserver   Derby

XXXXX     blob        XXXXX      image       XXXXX
XXXXX     clob        XXXXX      text        XXXXX
date      date        date       datetime    date    
                                                 
                                                 

2. create table
1. Oracle: default value should be ahead of [ column_constraint [, ... ]
CREATE [ [ LOCAL ] { TEMPORARY | TEMP } ] TABLE table_name ( { column_name data_type [ DEFAULT default_expr ] [ column_constraint [, ... ] ] | table_constraint } [, ... ]).....

Such as: name varchar2(16) default '' NOT NULL

3. how to insert "'" into databse with executing sql statement.
1.MSSQL: Use two "'" ("''") instead of "'".

4. How to insert a Date(datetime) field?
Mysql      date      '2004-01-01'
Oracle     date      to_date('01-01-2004', 'DD-MM-YYYY')
DB2        date      '2004-01-01 00:00:00.000'
Sqlserver  datetime  '2004-01-01'
Derby      date      '2004-01-01 00:00:00.000'

5. How to get current date&time?
ORACLE  SELECT   SYSDATE   FROM   DUAL      
DB2      SELECT   CURRENT   TIMESTAMP   FROM   SYSIBM.SYSDUMMY1      
SQLSERVER   SELECT   GETDATE()   FROM   TABLE      
MYSQL   mysql>   select   now();      
  mysql>   select   sysdate();      
  mysql>   select   curdate();      
  mysql>   select   current_date;      
  mysql>   select   curtime();      
  mysql>   select   current_time;