"ORACLE" SQL statement simple Application (iv) (11G)

Sort after adding nulls last in descending order, put null in the final

Select To_char (sysdate, ' Q ') from dual;

Dual pseudo-table public synonym because it has a record for easy reading

Select RowNum, ' A ' | | Rownum,mod (rownum,2) from dual connect by rownum<=10;

Select Rownum,to_date (' 2016-05-01 ', ' YYYY-MM-DD ') from dual connect by rownum<=10;

Select sysdate,sysdate+1/24,sysdate+1/1440 from dual;

Select To_char (sysdate, ' Fmyyyy-mm-dd h24:mi:ss ') from dual;

Select 100+NVL (null,0) from dual;

Select count (name), COUNT (1), COUNT (*) from T1;

Select COUNT (1) from T1;

group functions do not count null values

Union removes duplicate parts, sorts

Nuion all puts two sets together, does not remove duplicates, does not sort.

Intersect intersect

Default Defaults

only update set status=null this equals null condition

Delete does not lower the high water level, the deleted information is recorded in each article

Truncate lowers the high water level and completely removes

Number ( total number of digits, where several decimal points) The default value can be no parentheses and content

Timestamp(default 6 -bit can change) seconds with decimals

Blob(binary example: Photo storage)

Clob(character)

ORACLE SQL statement simple Application (iv) (11g)