Oracle DB Common Statements

1.

Altertable table name Add system Time field datedefaultsysdate;--new
altertable Table name MODIFY The field to be modified VARCHAR2 (12);--Modify

2.

The decode () function is one of the most powerful functions of Oracle PL/SQL and is currently available only to Oracle Corporation, and the SQL implementations of other database vendors do not yet have this function

DECODE (Value,if1,then1,if2,then2,if3,then3,..., else), which indicates that if value equals IF1, the result of the DECODE function returns THEN1,..., if it is not equal to any of the If values, The else is returned. At first glance, DECODE can only do equals test, but just see, we can use some function or calculation instead of value, it is possible to make the DECODE function more than, less than or equal to the function.

3.

NVL (string1, Replace_with)

Function: If string1 is null, the NVL function returns the value of Replace_with, otherwise the value of string1 is returned.

By extension, this NVL has the same effect as ISNULL (string1, replace_with) in SQL Server.

The function of NVL2 (E1, E2, E3) is: If E1 is null, the function returns E3 and if E1 is not NULL, E2 is returned.

Oracle DB Common Statements