I need to enforce uniqueness on specific data in a table (~10 million rows). This example data illustrates the rule -
For code=X the part# cannot be duplicate. For any other code there can be duplicate part#. e.g ID 8 row can't be there but ID 6 row is fine. There are several different codes in the table and part# but uniqueness is desired only for one code=X.
ID CODE PART#
1 A R0P98
2 X R9P01
3 A R0P98
4 A R0P44
5 X R0P44
6 A R0P98
7 X T0P66
8 X T0P66
The only way I see is to create a trigger on the table and check for PART# for code=X before insert or update. However, I fear this solution may slow down inserts and updates on this table.
Appreciate your help!
In Oracle, you can create a unique index on an expression for this:
create unique index myidx
on mytable (case when code = 'X' then part# end);
Related
I'm trying to create a new table on my DB, the table has 2 important columns
id_brands (This is an FK from the table brands)
id_veiculo
What I would like to have is something like this:
id_brands
id_veiculo
1
1
1
2
2
1
2
2
3
1
1
3
3
2
I create the table but I'm trying to find a way to make this condition with a trigger but without success, I don't know if it's possible or if a trigger is the best way to do that.
What you are probably trying to do, by the pattern of the example table, is setting up an auxiliary N to N relationship table.
In this case, by having another table, for id_veiculo and its properties, you will be able to have both ids as FKs. As for the primary key in this auxiliary table, it would be both id_brands and id_veiculo:
PRIMARY KEY (id_veiculo, id_brands);
Here's another Stackoverflow question about NxM/NxN relationships.
Also, it isn't very clear what you're trying to do with the table, but if it's the population/seeding of data, then yes, a Trigger is an viable solution.
pk_id unq_id content
1 1 foo
2 2 bar
3 1 foo
4 1 foo
5 3 baz
6 2 bar
7 4 qux
I am populating a table with known content that can repeat a random number of times.
I want to auto-generate the unq_id column which counts the nth appearance of the unique value in the content column.
I am thinking about some foreign key constraint but not particular sure how to construct this kind of constraint. Searching on the web for a long time without result, I can only ask here.
Could someone shed some light? Any help would be appreciated.
This is more simply done when you query the table, using row_number():
select pk_id, content,
row_number() over (partition by content order by pk_id) as unq_id
from t;
You can put this logic in a view.
Actually storing the value in the table requires a bit of work. If you don't pre-calculate the value, your'll need to use a trigger.
Alternatively, if the data does not change, then you can load into a staging table and use the above query to create the final table.
I have the following records inside a table:
User Product Quantity
A Test 1 5
A Test 1 3
B Test 1 4
B Test 2 1
When I run 'DELETE FROM Sample WHERE User='A' AND Product='Test 1', I want to delete the last inserted record:
User Product Quantity
A Test 1 5
B Test 1 4
B Test 2 1
Is this possible? Please advise.
Here's a working sql fiddle based on my comments.
Note that in the fiddle example I added an id and last_edited columns. I use GetDate() to fill the date time but add successive days( getdate() + 1..n ) to force unique date times...
The answer isn't the smoothest but demonstrates what I was talking about in the comments, and is correct. By the way, you didn't specify the version of SQL Server but if it's 2012 you should use the new, higher-precision date time type and also add a unique index on the column since your date times need to be unique identifiers in this scenario. Do you use the surrogate id though!
Repeating comments here:
What does "last" mean in your table? Without a date time column you cannot deterministically calculate which record was temporally placed last in the table. There is no internal metadata, in SQL Server at least, that would give you such info... I would also suggest using a surrogate primary key since none of your values are unique.
I have a simple join table with two id columns in SQL Server.
Is there any way to select all rows in the exact order they were inserted?
If I try to make a SELECT *, even if I don't specify an ORDER BY clause, the rows are not being returned in the order they were inserted, but ordered by the first key column.
I know it's a weird question, but this table is very big and I need to check exactly when a strange behavior has begun, and unfortunately I don't have a timestamp column in my table.
UPDATE #1
I'll try to explain why I'm saying that the rows are not returned in 'natural' order when I SELECT * FROM table without an ORDER BY clause.
My table was something like this:
id1 id2
---------------
1 1
2 2
3 3
4 4
5 5
5 6
... and so on, with about 90.000+ rows
Now, I don't know why (probably a software bug inserted these rows), but my table have 4.5 million rows and looks like this:
id1 id2
---------------
1 1
1 35986
1 44775
1 60816
1 62998
1 67514
1 67517
1 67701
1 67837
...
1 75657 (100+ "strange" rows)
2 2
2 35986
2 44775
2 60816
2 62998
2 67514
2 67517
2 67701
2 67837
...
2 75657 (100+ "strange" rows)
Crazy, my table have now millions of rows. I have to take a look when this happened (when the rows where inserted) because I have to delete them, but I can't just delete using *WHERE id2 IN (strange_ids)* because there are "right" id1 columns that belongs to these id2 columns, and I can't delete them, so I'm trying to see when exactly these rows were inserted to delete them.
When I SELECT * FROM table, it returns me ordered by id1, like the above table, and
the rows were not inserted in this order in my table. I think my table is not corrupted because is the second time that this strange behavior happens the same way, but now I have so many rows that I can delete manually like it was on 1st time. Why the rows are not being returned in the order they were inserted? These "strange rows" were definetely inserted yesterday and should be returned near the end of my table if I do a SELECT * without an ORDER BY, isn't it?
A select query with no order by does not retrieve the rows in any particular order. You have to have an order by to get an order.
SQL Server does not have any default method for retrieving by insert order. You can do it, if you have the information in the row. The best way is a primary key identity column:
TableId int identity(1, 1) not null primary key
Such a column is incremented as each row is inserted.
You can also have a CreatedAt column:
CreatedAt datetime default getdate()
However, this could have duplicates for simultaneous inserts.
The key point, though, is that a select with no order by clause returns an unordered set of rows.
As others have already written, you will not be able to get the rows out of the link table in the order they were inserted.
If there is some sort of internal ordering of the rows in one or both of the tables that this link table is joining, then you can use that to try to figure out when the link table rows have been created. Basically, they cannot have been created BEFORE both of the rows containing the PK:s have been created.
But on the other hand you will not be able to find out how long after they have been created.
If you have decent backups, you could try to restore one or a few backups of varying age and then try to see if those backups also contains this strange behaviour. It could give you at least some clue about when the strangeness has started.
But the bottom line is that using just a select, there is now way to get the row out of a table like this in the order they were inserted.
If SELECT * doesn't return them in 'natural' order and you didn't insert them with a timestamp or auto-incrementing ID then I believe you're sunk. If you've got an IDENTITY field, order by that.
But the question I have is, how can you tell that SELECT * isn't returning them in the order they were inserted?
Update:
Based on your update, it looks like there is no method by which to return records as you wish, I'd guess you've got a clustered index on ID1?
Select *, %%physloc%% as pl from table
order by pl desc
I just started using SQL and need to perform the following task.
1) First, I need to dupicate a table 100 times. For all these duplicated tables, I want to keep its content unchanged. But I also want to update the primary key by one.
2) Secend, I want to concatenate all these duplicated tables together by row, and also concatenate them to the original table by row.
Example: The original table looks like:
ID CATEGORY
1 A
2 B
… …
26 Z
And I want to duplicate this table, and concatenate it to the original one. I want to maintain the colums other than the primary key (ID here) unchanged, and update the primary key by one each time. I want to get:
ID CATEGORY
1 A
2 B
...
26 Z
27 A
...
52 Z
How to do this? Thanks!