longlongago

ALTER TABLE  tablename

RENAME COLUMN columnname  to newcolumnname;更改属性名称

 

System date : sysdate系统日期SYSDATE

 

SELECT *

                FROM instructor

                                WHERE TO_CHAR() (dateofjoining) LIKE '%MAR%';转为字符串用TO_CHAR()

 

SELECT *

                FROM applicant

                                WHERE emailid LIKE '%A_%' ESCAPE 'A';转义字符要用ESCAPE

SELECT COUNT(courseid)

                FROM registration

                                WHERE dateofexam BETWEEN '1-Jan-08' AND '30-May-08'; 日期要加单引号

 

CREATE USER beke2 IDENTIFIED BY beke_wang;

GRANT connect TO beke2;

GRANT resource TO beke2;

GRANT dba TO beke2;

 

system “Eserver@fp”

 

desc user_tables;

select table_name from user_names;

 

 

任何包含NULL的算术运算（+，-，*，/）应该返回一个空值NULL得结果；

任何包含NULL的关系运算（>，<）应该返回一个特殊的值unknown；

聚集函数除了COUNT（*）外的所有聚集函数都忽略输入集合中的空值NULL，

空集的COUNT运算为0，其它聚集函数在输入为空集的情况下返回一个空集。   

 

NVL(columnname,value)自动将NULL转换为某个数select  sum(NVL(salary,NULL))

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