Oracle Database experience series-Article 1

Oracle Database experience series-Article 1
1) change the date display type of the query results in SQL developer in oracle 11g r2, that is, the setting of the session date type:
Alter session set nls_date_format = 'yyyy-MM-DD HH24: MI: ss ';
Oracle field:
Alter table operator_daily add (op_type number (11 ));

2) The dense_rank () function is a continuous sorting. When there are two second names, it still follows the third name.

3) The rank () function is a skip sorting. When there are two second names, the next is the fourth one (also in each group)

4) View table constraints: Select * from user_constraints where table_name = 'parent ';

Constraint_type: c: check p: primary key r: foreign key u: unique

5) create tablespace mcp datafile 'e: \ oracle \ tablespace \ data. dbf' size 512 m;

6) when the oracle field is varchar2, The substr function is used for conversion, instead of tu_char.

7) when case when exists in the statement, the group by clause must be written into the conditions in case when. Otherwise, the group rules are not met;

8) backup table:
Create table table_name as select * from table_namexxx