I am using oracle database
While inserting a row in a table, i need to find the max value of a column and increment it by 1, and use that value in row i am inserting.
INSERT INTO dts_route
(ROUTE_ID, ROUTE_UID, ROUTE_FOLDER)
VALUES (
(SELECT MAX(ROUTE_ID) + 1 FROM route) ,
ROUTE_UID,
ROUTE_FOLDER)
This works fine if their is at least one entry in table. But returns null when their are no entries in table.
How can i get default value of 1 when their are no entries in table.
SELECT COALESCE(MAX(ROUTE_ID),0) ...
This is not a safe way of creating an auto-increment field. You can use an Oracle sequence to achieve this goal.
As for the null, you can use NVL
to give a default value (say, 0) in case the function returns null.
Use sequence for the ID. You need to create sequence. See below link
http://www.basis.com/onlinedocs/documentation/b3odbc/sql_sequences.htm
Use:
INSERT INTO dts_route
(ROUTE_ID)
SELECT COALESCE(MAX(r.route_id), 0) +1
FROM ROUTE r
...but you really should be using a sequence to populate the value with a sequential numeric value:
CREATE SEQUENCE dts_route_seq;
...
INSERT INTO dts_route
(ROUTE_ID)
SELECT dts_route_seq.NEXTVAL
FROM DUAL;
Set a default for NULL
SELECT NVL(MAX(ROUTE_ID),0)
though using a sequence might be easier if you don't mind the odd gaps in your route ids
select 0 when null, then it will be 0+1 which is a correct number compared to null+1
SELECT isnull(MAX(ROUTE_ID),0) + 1 FROM route
If you are concerned about there being gaps in your route ids then create the sequence with the NOCACHE clause:
CREATE SEQUENCE dts_route_seq NOCACHE;
Note that there is a performance hit because Oracle now has to "commit" each time you increment the sequence.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.