All about the DUAL
Posted by Sriram Sanka on May 4, 2011
The Magic table DUAL is owned by User SYS as its an dictionary object.
ind> select object_name,owner,object_type
2 from dba_objects
3 where object_name like ‘%DUAL%’;
OBJECT_NAME OWNER OBJECT_TYPE
———— ———————- ——————-
DUAL SYS TABLE
DUAL PUBLIC SYNONYM
2 rows selected.
‘Dual’ is a special table with 1X1 (1 row and 1 column) owned by sys which can be used to know the result I can say :).
ind> desc dual;
Name Null? Type
—————————————– ——– ————-
DUMMY VARCHAR2(1)
ind> desc x$dual
Name Null? Type
—————————————– ——– ———————-
ADDR RAW(4)
INDX NUMBER
INST_ID NUMBER
DUMMY VARCHAR2(1)
In specific cases like whenever Database is not fully up(recovery process),at that situation oracle reads the table dual from a fixed table/view
ind> select * from dual;
D
–
X
1 row selected.
ind> select * from x$dual;
ADDR INDX INST_ID D
——– ———- ———- –
0366CD54 0 1 X
1 row selected.
Never ever try to play with dual/dictionary objects which will ruin you DB.
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