I'm new to SQL beyond basic queries / inserts (as you'll see quickly as you read further)
Here's a (very) simplified example.
I have table 'person' like:
UID | NAME | AGE | LOCATION
45 | bob | 23 | Canada
31 | bill | 20 | Romania
and a second table 'person_history' like:
UID | PID | NAME | AGE | LOCATION
- | - | - | - | -
when I insert into this table like
update person set age=10 where UID==45
I want my trigger to fire, to access the existing values in person, and to push them into the second table, and then continue with the original insert.
The way I can think to do this is:
Select uid, name, age, location,
into v_uid, v_name, v_age, v_location
from person
where uid = :new.uid
then do the insert like
Insert into person_history(UID, PID, NAME, AGE, LOCATION)
VALUES (sequence.nextval, v_uid, v_name, v_age, v_location);
but this seems like a very round-about way of doing it - especially if the table has 50 columns.
Is this the correct method, and is there a more elegant way of approaching this problem.
Again, keep in mind how new I am to all of this, so examples would be really helpful.
why do you do this part?:
Select uid, name, age, location,
into v_uid, v_name, v_age, v_location
from person
where uid = :new.uid
Just use this approach:
INSERT INTO person_history(UID, PID, NAME, AGE, LOCATION)
VALUES (sequence.nextval, ::new.uid, ::new.name, ::new.age, ::new.location);
Regarding the quantity of columns, I'm not sure it is possible to do it in a "smarter" way.
Related
Consider the following table named UserAttributes:
+----+--------+----------+-----------+
| Id | UserId | AttrName | AttrValue |
+----+--------+----------+-----------+
| 4 | 1 | FavFood | Apples |
| 3 | 2 | FavFood | Burgers |
| 2 | 1 | FavShape | Circle |
| 1 | 1 | FavFood | Chicken |
+----+--------+----------+-----------+
I would like to insert a new record in this table if the latest version of a particular attribute for a user has a value that does not match the latest.
What I mean by the latest is, for example, if I was to do:
SELECT TOP(1) * FROM [UserAttributes] WHERE [UserId] = 1 AND [AttrName] = 'FavFood' ORDER BY [Id] DESC
I will be able to see that user ID 1's current favorite food is "Apples".
Is there a query safe for concurrency that will only insert a new favorite food if it doesn't match the current favorite food for this user?
I tried using the MERGE query with a HOLDLOCK, but the problem is that WHEN MATCHED/WHEN NOT MATCHED, and that works if I never want to insert a new record after a user has previously set their favorite food (in this example) to the new value. However, it does not consider that a user might switch to a new favorite food, then subsequently change back to their old favorite food. I would like to maintain all the changes as a historical record.
In the data set above, I would like to insert a new record if the user ID 1's new favorite food is "Burgers", but I do not want to insert a record if their new favorite food is "Apples" (since that is their current favorite food). I would also like to make this operation safe for concurrency.
Thank you for your help!
EDIT: I should probably also mention that when I split this operation into two queries (ie: first select their current favorite food, then do an insert query only if there is a new food detected) it works under normal conditions. However, we are observing race conditions (and therefore duplicates) since (as you may have guessed) the data set above is simply an example and there are many threads operating on this table at the same time.
A bit ugly, but to do it in one command, you could insert the user's (new) favorite food but filter with an EXCEPT of their current values.
e.g., (assuming the user's new data is in #UserID, #FavFood
; WITH LatestFavFood AS
(SELECT TOP(1) UserID, AttrName, AttrValue
FROM [UserAttributes]
WHERE [UserId] = #UserID AND [AttrName] = 'FavFood'
ORDER BY [Id] DESC
)
INSERT INTO UserAttributes (UserID, AttrName, AttrValue)
SELECT #UserID, 'FavFood', #FavFood
EXCEPT
SELECT UserID, AttrName, AttrValue
FROM LatestFavFood
Here's a DB_Fiddle with three runs.
EDIT: I have changed the above to assume varchar types for AttrName rather than nvarchar. The fiddle has a mixture. Would be good to ensure you get them correct (especially food as it may have special characters).
I am trying to create a INSERT SELECT statement which inserts and converts data from Imported_table to Destination_table.
Imported_table
+------------------+-----------------------+
| Id (varchar(10)) | genre (varchar(4000)) |
+------------------+-----------------------+
| 6 | Comedy |
+------------------+-----------------------+
| 5 | Comedy |
+------------------+-----------------------+
| 1 | Action |
+------------------+-----------------------+
Destination_table (How it should be looking)
+-----------------------------+----------------------------+
| genre_name (PK,varchar(50)) | description (varchar(255)) |
+-----------------------------+----------------------------+
| Comedy | Description of Comedy |
+-----------------------------+----------------------------+
| Action | Description of Action |
+-----------------------------+----------------------------+
Imported_table.Id isn't used at all but is still in this (old) table
Destination_table.genre_name is a primairy key and should be unique (distinct)
Destination_table.description is compiled with CONCAT('Description of ',genre)
My best try
INSERT INTO testdb.dbo.Destination_table (genre_name, description)
SELECT DISTINCT Genre,
LEFT(Genre,50) AS genre_name,
CAST(CONCAT('Description of ',Genre) AS varchar(255)) AS description
FROM MYIMDB.dbo.Imported_table
Gives the error: The select list for the INSERT statement contains more items than the insert list. The number of SELECT values must match the number of INSERT columns.
Thanks in advance.
The largest error in your query is that you are trying to insert 3 columns into a destination table having only two columns. That being said, I would just use LEFT for both inserted values and take as much space as the new table can hold:
INSERT INTO testdb.dbo.Destination_table (genre_name, description)
SELECT DISTINCT
LEFT(Genre, 50),
'Description of ' + LEFT(Genre, 240) -- 240 + 15 = 255
FROM MYIMDB.dbo.Imported_table;
As a side note, the original genre field is 4000 characters wide, and your new table structure runs the risk of throwing away a lot of information. It is not clear whether you are concerned with this, but it is worth pointing out.
This means your SELECT (genre, genre_name,description) and INSERT (genre_name, description) lists don't match. You need to SELECT the same number of fields as you are specifying in your INSERT.
Try this:
INSERT INTO testdb.dbo.Destination_table (genre_name, description)
SELECT DISTINCT Genre,
CAST(CONCAT('Description of ',Genre) AS varchar(255)) AS description
FROM MYIMDB.dbo.Imported_table
You have 3 columns in your SELECT, try:
INSERT INTO testdb.dbo.Destination_table (genre_name, description)
SELECT DISTINCT LEFT(Genre,50) AS genre_name,
CAST(CONCAT('Description of ',Genre) AS varchar(255)) AS description
FROM MYIMDB.dbo.Imported_table
Hello as the title suggest I need help writing a query that does this. I need to find all the users who have had a badge number change. So in the database there are often two records for the same person but both have a different badge number. Im assuming it's the same person if the social matches.
Table:
Badge_no | SSN
123123 | 387-47-1234 2
34837 | 387-47-1234
837532 | 543-45-6392
584391 | 543-45-6392
In this case I would want it to output:
837532 | 543-45-6392
584391 | 543-45-6392
Thank you!
I believe the following should do the trick here:
SELECT *
FROM yourtable
WHERE SSN IN (SELECT SSN FROM yourtable GROUP BY SSN HAVING Count(*) >=2);
That subquery will return SSN's that have more than one record. We use those SSN's to select, again, from the table to get all of the fields associated to them.
How can I create a table without knowing in advance how many and what columns it exactly holds?
The idea is that I have a table DATA that has 3 columns : ID, NAME, and VALUE
What I need is a way to get multiple values depending on the value of NAME - I can't do it with simple WHERE or JOIN (because I'll need other values - with other NAME values - later on in my query).
Because of the way this table is constructed I want to PIVOT it in order to transform every distinct value of NAME into a column so it will be easier to get to it in my later search.
What I want now is to somehow save this to a temp table / variable so I can use it later on to join with the result of another query...
So example:
Columns:
CREATE TABLE MainTab
(
id int,
nameMain varchar(max),
notes varchar(max)
);
CREATE TABLE SecondTab
(
id int,
id_mainTab, int,
nameSecond varchar(max),
notes varchar(max)
);
CREATE TABLE DATA
(
id int,
id_second int,
name varchar(max),
value varchar(max)
);
Now some example data from the table DATA:
| id | id_second_int | name | value |
|-------------------------------------------------------|
| 1 | 5550 | number | 111115550 |
| 2 | 6154 | address | 1, First Avenue |
| 3 | 1784 | supervisor | John Smith |
| 4 | 3467 | function | Marketing |
| 5 | 9999 | start_date | 01/01/2000 |
::::
Now imagine that 'name' has A LOT of different values, and in one query I'll need to get a lot of different values depending on the value of 'name'...
That's why I pivot it so that number, address, supervisor, function, start_date, ... become colums.
This I do dynamically because of the amount of possible columns - it would take me a while to write all of them in an 'IN' statement - and I don't want to have to remember to add it manually every time a new 'name' value gets added...
herefore I followed http://sqlhints.com/2014/03/18/dynamic-pivot-in-sql-server/
the thing is know that I want the result of my execute(#query) to get stored in a tempTab / variable. I want to use it later on to join it with mainTab...
It would be nice if I could use #cols (which holds the values of DATA.name) but I can't seem to figure out a way to do this.
ADDITIONALLY:
If I use the not dynamic way (write down all the values manually after 'IN') I still need to create a column called status. Now in this column (so far it's NULL everywhere because that value doesn't exist in my unpivoted table) i want to have 'open' or 'closed', depending on the date (let's say i have start_date and end_date,
CASE end_date
WHEN end_date < GETDATE() THEN pivotTab.status = 'closed'
ELSE pivotTab.status = 'open'
Where can I put this statement? Let's say my main query looks like this:
SELECT * FROM(
(SELECT id_second, name, value, id FROM TABLE_DATA) src
PIVOT (max(value) FOR name IN id, number, address, supervisor, function, start_date, end_date, status) AS pivotTab
JOIN SecondTab ON SecondTab.id = pivotTab.id_second
JOIN MainTab ON MainTab.id = SecondTab.id_mainTab
WHERE pivotTab.status = 'closed';
Well, as far as I can understand - you have some select statement and just need to "dump" its result to some temporary table. In this case you can use select into syntax like:
select .....
into #temp_table
from ....
This will create temporary table according to columns in select statement and populate it with data returned by select datatement.
See MDSN for reference.
Suppose I have a table foo with schema (name, age). So the table looks like:
NAME | AGE
John | 20
Jane | 50
Jason | 30
Now suppose I wanted to select from this table, but I wanted to change all their ages to 20 via the select query. That is, I don't want to update the original table foo, but I want to select, something like:
SELECT name, 20 as age from foo
In other words, I want to manipulate the data on the select. Of course, my real-life example is much more complicated than this but knowing the answer to this will do. Thanks!
You basically just do what you put in your question:
SELECT name, newValue as age
from yourTable
This will give you the name from your table and then the value you specify for the other column.
See SQL Fiddle with Demo