I'm aware of using RETURNING in an INSERT statement but need a way to either have it returned as a result of the INSERT statement (or enclosing transaction) or be able to retrieve that value using SELECT. Is there a way to do this? I cannot use DBMS_OUTPUT. Thanks!
RETURNING clause is the easiest way to guarantee getting the value of the ID generated by an INSERT statement. Querying for max(id) is unreliable in a multi-user environment, especially if you're using RAC.
If the ID is populated from a sequence you can get the current value of the sequence by running this in the same session as the INSERT:
select your_sequence.currval from dual;
This means you need to know the name of the sequence, which isn't always obvious, even more so if you're using 12c Identity columns.
Basically, if you want the ID use RETURNING.
Related
with FireDac, How to get last inserted id on ms sql server?
thanks
Make the that id to a identity column and then get it by Using
SELECT SCOPE_IDENTITY()
after the insert statement
Please refer the following links
http://msdn.microsoft.com/en-us/library/ms190315.aspx
Use auto-incremented field type
http://www.da-soft.com/anydac/docu/Auto-Incremental_Fields.html
This would provide for code like
DataSet.Insert;
....
DataSet.Post;
id := DataSet.FieldByName('ID').AsInteger;
Another approach might be crafting proper SQL statements like described at
http://en.wikipedia.org/wiki/Insert_(SQL)#Retrieving_the_key
SQL Server - Return value after INSERT
Best way to get identity of inserted row?
AnyDAC author also suggests a special method to fetch DBMS-specific toolings via http://docs.embarcadero.com/products/rad_studio/firedac/uADCompClient_TADCustomConnection_GetLastAutoGenValue#String.html
But all those post-factum requests with SELECT ##identity or SELECT SCOPE_IDENTITY are fragile and dangerous. When you insert data into table A, its triggers may insert data into related tables B and C, and identity would recall C's autoinc, rather than table where you started inserting at.
I'm connecting to a DB2 database and executing SQL statements.
One example of what is being done is:
select field from library/file
[program code line finishes executing]
[increment value by one]
update library/file set field = 'incremented value'
I have a need to immediately update the value while returning the value. Rather than having to wait for the script to complete, and then run a separate UPDATE statement.
The concept of what I would like to do is this:
select field from library/file; update library/file set field = (Current Value + 1); go;
Please note... this is not the common SQL database most would be familiar with, it is a DB2 database on an IBM i.
Thanks!
Consider using a DB2 SEQUENCE to manage the next available number, if this file is simply intended to have a single row storing your counter. That is what a SEQUENCE is designed to do.
To set it up, use a CREATE SEQUENCE statement.
To increment the value and retrieve, use a SEQUENCE reference expression of the form NEXT VALUE FOR sequence-name. To find out what the most recent value was, use the PREVIOUS VALUE FOR sequence-name. These expressions can be used like a regular any column expression, such as in a SELECT or INSERT statement.
Suppose, for example you want to do this for invoice numbers (and maybe your accounting department doesn't want their first invoice number to be 000001, so we will initialize it higher).
CREATE SEQUENCE InvoiceSeq
as decimal (7,0)
start with 27000; -- for example
You could get a number for a new invoice like this:
SELECT NEXT VALUE FOR InvoiceSeq
INTO :myvar
FROM SYSIBM/SYSDUMMY1;
But what is this SYSIBM/SYSDUMMY1 table? We're not really getting anything from table, so why are we pretending to do so? The SELECT needs a FROM-table clause. But since we don't need one, let's use a VALUES INTO statement.
VALUES NEXT VALUE FOR InvoiceSeq
INTO :myvar;
So that has incremented the counter, and put the value into our variable. You could use that value to INSERT into our InvoiceHeaders and InvoiceDetails tables.
Or, you could increment the counter as you write an InvoiceHeader, then use it again when writing the InvoiceDetails.
INSERT INTO InvoiceHeaders
(InvoiceNbr, Customer, InvoiceDate)
VALUES (NEXT VALUE FOR InvoiceSeq, :custnbr, :invdate);
for each invoice detail
INSERT INTO InvoiceDetails
(InvoiceNbr, InvoiceLine, Reason, Fee)
VALUES (PREVIOUS VALUE FOR InvoiceSeq, :line, :itemtxt, :amt);
The PREVIOUS VALUE is local to the particular job, so there should be no risk of another job getting the same number.
update library/file set field = field + 1;
select field from library/file;
[program code line finishes executing]
[increment value by one]
This handles the problem of another app updating the number between the time you fetch it and the time you update it. Update it and then use it. If two apps try to update simultaneously, one will wait.
A SEQUENCE object is designed exactly for this purpose, but if you are forced to keep this 'next ID' file updated, this is how I'd do it. Follow the link in the comment by #Clockwork-Muse for info on the SEQUENCE object, or try this example from V5R4.
His request is like this:
UPDATE sometable
SET somecounter = somecounter + 10,
:returnvar = somecounter + 10;
Updates and retrieves at the same time.
This is possible in MSSQL, In fact I use it alot there,
but DB2 doesnt seem to have this feature.
I am working on implementing an on-demand SQL cache table for an application so I have
CacheTable with columns Type, Number, Value
Then I have a function called GetValue( Type, Number )
So I want to have a function that does the following
If (CacheTable contains Type, Number) then return value
Else call GetValue( Type, Number) and put that value into CacheTable and return the Value
Does anyone know the most elegant way to do this?
I was thinking of using a SQL merge.
Not sure how elegant one can get, but we might do it just the way you describe. Query the database
select Value from Tab1 where Type=#type and Number=#num
and if no rows are returned, compute the value, then store it in the database for next time.
However, if the "compute the value" requires the database itself, and we can compute it in the database, then we can do the whole cycle with one database round trip -- more 'elegant' perhaps but faster at least than 3 round trips (lookup, compute, store).
declare #val int
select #val=Value from Tab1 where Type=#type and Number=#num
if ##ROWCOUNT=0 BEGIN
exec compute_val #type,#num,#val OUTPUT
insert into Tab1 values (#type,#num,#val)
END
SELECT #val[Value]--return
The only use for SQL Merge is if you think there may be concurrent users and the number is inserted between above select and insert, giving an error on the insert. I'd just catch the error and skip the insert (as we can assume the value won't be different by definition).
So I'm trying to run some SQL here through PHP's PDO (which I don't believe should be the problem) like such:
INSERT INTO example (
d_id,
s_id
)
VALUES (
currval('d_id_seq'),
currval('s_id_seq')
);
I have two sequences called d_id_seq and s_id_sec (lets pretend I have a table named d and a table named s, and this sequence is a column called ID and serial type).
Now, obviously I'm doing this wrong, as I get an error about the sequence not being used in this session:
Object not in prerequisite state: 7 ERROR: currval of sequence "d_id_seq" is not yet defined in this session
So, how should I write this?
Problem can be solved via the following command:
SELECT last_value FROM d_id_seq;
Note that I'm using PostgreSQL 9.1.9, I do not know about other or older versions.
The error means you did not "use" the sequence in this session (postgres connection). For instance you did not do any INSERTs on the table d.
Perhaps you have a bug in your code and reconnect to postgres after each query ?
A more convenient way to do it is to use INSERT RETURNING on your INSERTs. Then you get the ids.
From the fine manual:
currval
Return the value most recently obtained by nextval for this sequence in the current session. (An error is reported if nextval has never been called for this sequence in this session.) Because this is returning a session-local value, it gives a predictable answer whether or not other sessions have executed nextval since the current session did.
You use currval to get the last value that was pulled out of the sequence in the current session. The usual pattern is to do an INSERT that uses a sequence and then you call currval to figure out what value the INSERT used. If you haven't called nextval with the sequence in question in the current session then there is nothing for currval to return.
Maybe you're actually looking for select max(id) from d and select max(id) from s:
INSERT INTO example (d_id, s_id)
SELECT MAX(d.id), MAX(s.id)
FROM d, s;
Or maybe you need to wrap your d and s inserts in a stored procedure that takes care of inserting in all three tables at once.
I have a table that looks a bit like this actors(forename, surname, stage_name);
I want to update stage_name to have a default value of
forename." ".surname
So that
insert into actors(forename, surname) values ('Stack', 'Overflow');
would produce the record
'Stack' 'Overflow' 'Stack Overflow'
Is this possible?
Thanks :)
MySQL does not support computed columns or expressions in the DEFAULT option of a column definition.
You can do this in a trigger (MySQL 5.0 or greater required):
CREATE TRIGGER format_stage_name
BEFORE INSERT ON actors
FOR EACH ROW
BEGIN
SET NEW.stage_name = CONCAT(NEW.forename, ' ', NEW.surname);
END
You may also want to create a similar trigger BEFORE UPDATE.
Watch out for NULL in forename and surname, because concat of a NULL with any other string produces a NULL. Use COALESCE() on each column or on the concatenated string as appropriate.
edit: The following example sets stage_name only if it's NULL. Otherwise you can specify the stage_name in your INSERT statement, and it'll be preserved.
CREATE TRIGGER format_stage_name
BEFORE INSERT ON actors
FOR EACH ROW
BEGIN
IF (NEW.stage_name IS NULL) THEN
SET NEW.stage_name = CONCAT(NEW.forename, ' ', NEW.surname);
END IF;
END
According to 10.1.4. Data Type Default Values no, you can't do that. You can only use a constant or CURRENT_TIMESTAMP.
OTOH if you're pretty up-to-date, you could probably use a trigger to accomplish the same thing.
My first thought is if you have the two values in other fields what is the compelling need for redundantly storing them in a third field? It flies in the face of normalization and efficiency.
If you simply want to store the concatenated value then you can simply create a view (or IMSNHO even better a stored procedure) that concatenates the values into a pseudo actor field and perform your reads from the view/sproc instead of the table directly.
If you absolutely must store the concatenated value you could handle this in two ways:
1) Use a stored procedure to do your inserts instead of straight SQL. This way you can receive the values and construct a value for the field you wish to populate then build the insert statement including a concatenated value for the actors field.
2) So I don't draw too many flames, treat this suggestion with kid gloves. Use only as a last resort. You could hack this behavior by adding a trigger to build the value if it is left null. Generally, triggers are not good. They add unseen cost and interactions to fairly simple interactions. You can, though, use the CREATE TRIGGER to update the actors field after a record is inserted or updated. Here is the reference page.
As of MySQL 8.0.13, you can use DEFAULT clause for a column which can be a literal constant or an expression.
If you want to use an expression then, simply enclose the required expression within parentheses.
(concat(forename," ",surname))
There are two ways to accomplish what you are trying to do as per my knowledge:
(important: consider backing up your table first before running below queries)
1- Drop the column "stage_name" all together and create a new one with DEFAULT constraint.
ALTER TABLE actors ADD COLUMN stage_name VARCHAR(20) DEFAULT (concat(forename," ",surname))
2- This will update newer entries in the column "stage_name" but not the old ones.
ALTER TABLE actors alter stage_name set DEFAULT (concat(forename," ",surname));
After that, if you need to update the previous values in the column "stage_name" then simply run:
UPDATE actors SET stage_name=(concat(forename," ",surname));
I believe this should solve your problem.