How to know database initialization parameter in oracle

1)SHOW PARAMETER option: If you use SQL*Plus then you can use SHOW PARAMETER parameter_name to display the values of parameters currently in use. Note that with toad or tora you can't use it as it is SQL*plus option.

SQL>SHOW PARAMETERS sga_target;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
sga_target big integer 160M

2)Query from V$PARAMETER: You can query value column of this view to display the values of parameters currently in effect.

SQL> SELECT VALUE FROM v$PARAMETER WHERE name='sga_target';
VALUE
--------------------------------------------------------------------------------
167772160

3)Query from V$PARAMETER2: You can query value column of this view to display the values of parameters currently in effect. It is easier to distinguish list parameter values in this view because each list parameter value appears as a row.

4)Query from V$SPPARAMETER: You can query value column of this view to display the current contents of the server parameter file. The view returns FALSE values in the ISSPECIFIED column if a server parameter file is not being used by the instance.

5)Query from V$SYSTEM_PARAMETER: In this view it displays what will be the value if a new session inherits parameter values from the instance-wide values.

6)Query from V$SYSTEM_PARAMETER2: It displays the information about initialization parameters that are currently in effect for the instance, with each list parameter value appearing as a row in the view. A new session inherits parameter values from the instance-wide values.

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Difference between V$parameter and v$spparameter