What is the dual table in Oracle

Question

I ve heard people referring to this table and was not sure what it was about

User · Answer

It s a object to put in the from that return 1 empty row  For example  select 1 from dual  returns 1  select 21 44 from dual  returns 65  select  sequence  nextval from dual  returns the next value from the sequence

User · Answer

From Wikipedia  History  The DUAL table was created by Chuck Weiss of Oracle corporation to provide a table for joining in internal views      I created the DUAL table as an underlying object in the Oracle Data Dictionary  It was never meant to be seen itself  but instead used   inside a view that was expected to be queried  The idea was that you   could do a JOIN to the DUAL table and create two rows in the result   for every one row in your table  Then  by using GROUP BY  the   resulting join could be summarized to show the amount of storage for   the DATA extent and for the INDEX extent s   The name  DUAL  seemed   apt for the process of creating a pair of rows from just one  1   It may not be obvious from the above  but the original DUAL table had two rows in it  hence its name   Nowadays it only has one row   Optimization  DUAL was originally a table and the database engine would perform disk IO on the table when selecting from DUAL  This disk IO was usually logical IO  not involving physical disk access  as the disk blocks were usually already cached in memory  This resulted in a large amount of logical IO against the DUAL table   Later versions of the Oracle database have been optimized and the database no longer performs physical or logical IO on the DUAL table even though the DUAL table still actually exists

User · Answer

I think this wikipedia article may help clarify   http   en wikipedia org wiki DUAL table     The DUAL table is a special one-row   table present by default in all Oracle   database installations  It is suitable   for use in selecting a pseudocolumn   such as SYSDATE or USER The table has   a single VARCHAR2 1  column called   DUMMY that has a value of  X

User · Answer

A utility table in Oracle with only 1 row and 1 column  It is used to perform a number of arithmetic operations and can be used generally where one needs to generate a known output   SELECT   FROM dual   will give a single row  with a single column named  DUMMY  and a value of  X  as shown here     DUMMY -----  X

User · Answer

The DUAL table is a special one-row table present by default in all Oracle database installations  It is suitable for use in selecting a pseudocolumn such as SYSDATE or USER  The table has a single VARCHAR2 1  column called DUMMY that has a value of  X   You can read all about it in http   en wikipedia org wiki DUAL table

User · Answer

It s the special table in Oracle  I often use it for calculations or checking system variables  For example    Select 2 4 from dual prints out the result of the calculation Select sysdate from dual prints the server current date

User · Answer

It is a dummy table with one element in it  It is useful because Oracle doesn t allow statements like   SELECT 3 4   You can work around this restriction by writing   SELECT 3 4 FROM DUAL   instead

User · Answer

DUAL is necessary in PL SQL development for using functions that are only available in SQL  e g   DECLARE x XMLTYPE  BEGIN SELECT xmlelement  hhh    stuff   INTO x FROM dual  END

User · Answer

It is a dummy table with one element in it  It is useful because Oracle doesn t allow statements like   SELECT 3 4   You can work around this restriction by writing   SELECT 3 4 FROM DUAL   instead

User · Answer

I think this wikipedia article may help clarify   http   en wikipedia org wiki DUAL table     The DUAL table is a special one-row   table present by default in all Oracle   database installations  It is suitable   for use in selecting a pseudocolumn   such as SYSDATE or USER The table has   a single VARCHAR2 1  column called   DUMMY that has a value of  X

User · Answer

It s a sort of dummy table with a single record used for selecting when you re not actually interested in the data  but instead want the results of some system function in a select statement   e g  select sysdate from dual   See http   www adp-gmbh ch ora misc dual html

User · Answer

It is a dummy table with one element in it  It is useful because Oracle doesn t allow statements like   SELECT 3 4   You can work around this restriction by writing   SELECT 3 4 FROM DUAL   instead

User · Answer

The DUAL table is a special one-row table present by default in all Oracle database installations  It is suitable for use in selecting a pseudocolumn such as SYSDATE or USER  The table has a single VARCHAR2 1  column called DUMMY that has a value of  X   You can read all about it in http   en wikipedia org wiki DUAL table

User · Answer

The DUAL is special one row  one column table present by default in all Oracle databases  The owner of DUAL is SYS   DUAL is a table automatically created by Oracle Database along with the data functions  It is always used to get the operating systems functions like date  time  arithmetic expression   etc     SELECT SYSDATE from dual

User · Answer

DUAL is necessary in PL SQL development for using functions that are only available in SQL  e g   DECLARE x XMLTYPE  BEGIN SELECT xmlelement  hhh    stuff   INTO x FROM dual  END

User · Answer

From Wikipedia  History  The DUAL table was created by Chuck Weiss of Oracle corporation to provide a table for joining in internal views      I created the DUAL table as an underlying object in the Oracle Data Dictionary  It was never meant to be seen itself  but instead used   inside a view that was expected to be queried  The idea was that you   could do a JOIN to the DUAL table and create two rows in the result   for every one row in your table  Then  by using GROUP BY  the   resulting join could be summarized to show the amount of storage for   the DATA extent and for the INDEX extent s   The name  DUAL  seemed   apt for the process of creating a pair of rows from just one  1   It may not be obvious from the above  but the original DUAL table had two rows in it  hence its name   Nowadays it only has one row   Optimization  DUAL was originally a table and the database engine would perform disk IO on the table when selecting from DUAL  This disk IO was usually logical IO  not involving physical disk access  as the disk blocks were usually already cached in memory  This resulted in a large amount of logical IO against the DUAL table   Later versions of the Oracle database have been optimized and the database no longer performs physical or logical IO on the DUAL table even though the DUAL table still actually exists

User · Answer

The DUAL is special one row  one column table present by default in all Oracle databases  The owner of DUAL is SYS   DUAL is a table automatically created by Oracle Database along with the data functions  It is always used to get the operating systems functions like date  time  arithmetic expression   etc     SELECT SYSDATE from dual

User · Answer

It s a sort of dummy table with a single record used for selecting when you re not actually interested in the data  but instead want the results of some system function in a select statement   e g  select sysdate from dual   See http   www adp-gmbh ch ora misc dual html

User · Answer

DUAL is necessary in PL SQL development for using functions that are only available in SQL  e g   DECLARE x XMLTYPE  BEGIN SELECT xmlelement  hhh    stuff   INTO x FROM dual  END

User · Answer

DUAL we mainly used for getting the next number from the sequences   Syntax   SELECT  sequence name  NEXTVAL FROM DUAL    This will return the one row one column value NEXTVAL column name

User · Answer

DUAL we mainly used for getting the next number from the sequences   Syntax   SELECT  sequence name  NEXTVAL FROM DUAL    This will return the one row one column value NEXTVAL column name

User · Answer

It is a dummy table with one element in it  It is useful because Oracle doesn t allow statements like   SELECT 3 4   You can work around this restriction by writing   SELECT 3 4 FROM DUAL   instead

User · Answer

It s the special table in Oracle  I often use it for calculations or checking system variables  For example    Select 2 4 from dual prints out the result of the calculation Select sysdate from dual prints the server current date

User · Answer

It s a sort of dummy table with a single record used for selecting when you re not actually interested in the data  but instead want the results of some system function in a select statement   e g  select sysdate from dual   See http   www adp-gmbh ch ora misc dual html

User · Answer

Kind of a pseudo table you can run commands against and get back results  such as sysdate  Also helps you to check if Oracle is up and check sql syntax  etc

User · Answer

another situation which requires  select     from dual   is when we want to retrieve the code  data definition  for different database objects  like TABLE  FUNCTION  TRIGGER  PACKAGE   using the built in DBMS METADATA GET DDL function   select DBMS METADATA GET DDL  TABLE    lt table name gt    from DUAL   select DBMS METADATA GET DDL  FUNCTION    lt function name gt    from DUAL    in is true that nowadays the IDEs do offer the capability to view the DDL of a table  but in simpler environments like SQL Plus this can be really handy   EDIT  a more general situation  basically  when we need to use any PL SQL procedure inside a standard SQL statement  or when we want to call a procedure from the command line   select my function  lt input params gt   from dual    both recipes are taken from the book  Oracle PL SQL Recipes  by Josh Juneau and Matt Arena

User · Answer

More Facts about the DUAL      http   asktom oracle com pls asktom f p 100 11 0    P11 QUESTION ID 1562813956388  Thrilling experiments done here  and more thrilling explanations by Tom

User · Answer

It s a object to put in the from that return 1 empty row  For example  select 1 from dual  returns 1  select 21 44 from dual  returns 65  select  sequence  nextval from dual  returns the next value from the sequence

User · Answer

From Wikipedia  History  The DUAL table was created by Chuck Weiss of Oracle corporation to provide a table for joining in internal views      I created the DUAL table as an underlying object in the Oracle Data Dictionary  It was never meant to be seen itself  but instead used   inside a view that was expected to be queried  The idea was that you   could do a JOIN to the DUAL table and create two rows in the result   for every one row in your table  Then  by using GROUP BY  the   resulting join could be summarized to show the amount of storage for   the DATA extent and for the INDEX extent s   The name  DUAL  seemed   apt for the process of creating a pair of rows from just one  1   It may not be obvious from the above  but the original DUAL table had two rows in it  hence its name   Nowadays it only has one row   Optimization  DUAL was originally a table and the database engine would perform disk IO on the table when selecting from DUAL  This disk IO was usually logical IO  not involving physical disk access  as the disk blocks were usually already cached in memory  This resulted in a large amount of logical IO against the DUAL table   Later versions of the Oracle database have been optimized and the database no longer performs physical or logical IO on the DUAL table even though the DUAL table still actually exists

User · Answer

Kind of a pseudo table you can run commands against and get back results  such as sysdate  Also helps you to check if Oracle is up and check sql syntax  etc

User · Answer

From Wikipedia  History  The DUAL table was created by Chuck Weiss of Oracle corporation to provide a table for joining in internal views      I created the DUAL table as an underlying object in the Oracle Data Dictionary  It was never meant to be seen itself  but instead used   inside a view that was expected to be queried  The idea was that you   could do a JOIN to the DUAL table and create two rows in the result   for every one row in your table  Then  by using GROUP BY  the   resulting join could be summarized to show the amount of storage for   the DATA extent and for the INDEX extent s   The name  DUAL  seemed   apt for the process of creating a pair of rows from just one  1   It may not be obvious from the above  but the original DUAL table had two rows in it  hence its name   Nowadays it only has one row   Optimization  DUAL was originally a table and the database engine would perform disk IO on the table when selecting from DUAL  This disk IO was usually logical IO  not involving physical disk access  as the disk blocks were usually already cached in memory  This resulted in a large amount of logical IO against the DUAL table   Later versions of the Oracle database have been optimized and the database no longer performs physical or logical IO on the DUAL table even though the DUAL table still actually exists

User · Answer

I think this wikipedia article may help clarify   http   en wikipedia org wiki DUAL table     The DUAL table is a special one-row   table present by default in all Oracle   database installations  It is suitable   for use in selecting a pseudocolumn   such as SYSDATE or USER The table has   a single VARCHAR2 1  column called   DUMMY that has a value of  X

User · Answer

A utility table in Oracle with only 1 row and 1 column  It is used to perform a number of arithmetic operations and can be used generally where one needs to generate a known output   SELECT   FROM dual   will give a single row  with a single column named  DUMMY  and a value of  X  as shown here     DUMMY -----  X

User · Answer

another situation which requires  select     from dual   is when we want to retrieve the code  data definition  for different database objects  like TABLE  FUNCTION  TRIGGER  PACKAGE   using the built in DBMS METADATA GET DDL function   select DBMS METADATA GET DDL  TABLE    lt table name gt    from DUAL   select DBMS METADATA GET DDL  FUNCTION    lt function name gt    from DUAL    in is true that nowadays the IDEs do offer the capability to view the DDL of a table  but in simpler environments like SQL Plus this can be really handy   EDIT  a more general situation  basically  when we need to use any PL SQL procedure inside a standard SQL statement  or when we want to call a procedure from the command line   select my function  lt input params gt   from dual    both recipes are taken from the book  Oracle PL SQL Recipes  by Josh Juneau and Matt Arena

User · Answer

Kind of a pseudo table you can run commands against and get back results  such as sysdate  Also helps you to check if Oracle is up and check sql syntax  etc

User · Answer

It s a object to put in the from that return 1 empty row  For example  select 1 from dual  returns 1  select 21 44 from dual  returns 65  select  sequence  nextval from dual  returns the next value from the sequence

User · Answer

The DUAL table is a special one-row table present by default in all Oracle database installations  It is suitable for use in selecting a pseudocolumn such as SYSDATE or USER  The table has a single VARCHAR2 1  column called DUMMY that has a value of  X   You can read all about it in http   en wikipedia org wiki DUAL table

User · Answer

More Facts about the DUAL      http   asktom oracle com pls asktom f p 100 11 0    P11 QUESTION ID 1562813956388  Thrilling experiments done here  and more thrilling explanations by Tom

User · Answer

It s a object to put in the from that return 1 empty row  For example  select 1 from dual  returns 1  select 21 44 from dual  returns 65  select  sequence  nextval from dual  returns the next value from the sequence

User · Answer

It s the special table in Oracle  I often use it for calculations or checking system variables  For example    Select 2 4 from dual prints out the result of the calculation Select sysdate from dual prints the server current date

User · Answer

It s a sort of dummy table with a single record used for selecting when you re not actually interested in the data  but instead want the results of some system function in a select statement   e g  select sysdate from dual   See http   www adp-gmbh ch ora misc dual html

User · Answer

DUAL is necessary in PL SQL development for using functions that are only available in SQL  e g   DECLARE x XMLTYPE  BEGIN SELECT xmlelement  hhh    stuff   INTO x FROM dual  END

User · Answer

Kind of a pseudo table you can run commands against and get back results  such as sysdate  Also helps you to check if Oracle is up and check sql syntax  etc

User · Answer

The DUAL table is a special one-row table present by default in all Oracle database installations  It is suitable for use in selecting a pseudocolumn such as SYSDATE or USER  The table has a single VARCHAR2 1  column called DUMMY that has a value of  X   You can read all about it in http   en wikipedia org wiki DUAL table

User · Answer

It s the special table in Oracle  I often use it for calculations or checking system variables  For example    Select 2 4 from dual prints out the result of the calculation Select sysdate from dual prints the server current date

User · Answer

I think this wikipedia article may help clarify   http   en wikipedia org wiki DUAL table     The DUAL table is a special one-row   table present by default in all Oracle   database installations  It is suitable   for use in selecting a pseudocolumn   such as SYSDATE or USER The table has   a single VARCHAR2 1  column called   DUMMY that has a value of  X

[oracle] What is the dual table in Oracle?

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