In an update statement for a temp table, how does SQL Server decide which value to use when there are multiple values returned, for example:
UPDATE A
SET A.dte_start_date = table1.dte_start_date
FROM #temp_table A
INNER JOIN table1 ON A.id = table1.id
In this situation the problem is more than one dte_start_date is returned for each id value in the temp table. There is there's no index or unique value in the tables I'm working on so I need to know how SQL Server will choose between the different values.
It is non-deterministic. See the following example for a better understanding. Though it is not exactly the same scenario explained here, it is pretty similar
When the single value is to be retrieved from the database also use the SET statement with a query to set the value. For example:
SET #v_user_user_id = (SELECT u.user_id FROM users u WHERE u.login = #v_login);
Reason: Unlike Oracle, SQL Server does not raise an error if more than one row is returned from a SELECT query that is used to populate variables. The above query will throw an exception whereas the following will not throw an exception and the variable will contain a random value from the queried table(s).
SELECT #v_user_user_id = u.user_id FROM users u WHERE u.login = #v_login;
It is non-deterministic which value is used if you have a one two many relationship.
In MS-SQL-Sever (>=2005) i would use a CTE since it's a readable way to specify what i want using ROW_NUMBER. Another advantage of a CTE is that you can change it easily to do a select instead of an update(or delete) to see what will happen.
Assuming that you want the latest record(acc.to dte_start_date) for every id:
WITH CTE AS
(
SELECT a.*, rn = ROW_NUMBER() OVER (PARTITION BY a.id
ORDER BY a.dte_start_date DESC)
FROM #temp_table A
INNER JOIN table1 ON A.id = table1.id
)
UPDATE A
SET A.dte_start_date = table1.dte_start_date
FROM #temp_table A INNER JOIN CTE ON A.ID = CTE.ID
WHERE CTE.RN = 1
Related
I've a list of dates: list_of_dates.
I want to find the max and min values of each number with this code (#1).
It works how it should, and therefore I get the table MinMax
Now I want to update a other list (list_of_things) with these newly acquired values (#2).
However, it is not possible.
I assume it's due to DISTINCT and the fact that I always get two rows per number, each with the min and max values. Therefore an update is not possible.
Unfortunately I don't know any other way.
#1
SELECT a.number, b.MaxDateTime, c.MinDateTime
FROM (list_of_dates AS a
INNER JOIN (
SELECT a.number, MAX(a.dat) AS MaxDateTime
FROM list_of_dates AS a
GROUP BY a.number) AS b
ON a.number = b.number)
INNER JOIN (SELECT a.number, MIN(a.dat) AS MinDateTime
FROM list_of_dates AS a
GROUP BY a.number) AS c
ON a.number = c.number;
#2
UPDATE list_of_things AS a
LEFT JOIN MinMax AS b
ON a.number = b.number
SET a.latest = b. MaxDateTime, a.ealiest = b.MinDateTime```
No part of an MS Access update query can contain aggregation, else the resulting recordset becomes 'not updateable'.
In your case, the use of the min & max aggregate functions within the MinMax subquery cause the final update query to become not updateable.
Whilst it is not always advisable to store aggregated data (in favour of generating an output from transactional data using queries), if you really need to do this, here are two possible methods:
1. Using a Temporary Table to store the Aggregated Result
Run a select into query such as the following:
select
t.number,
max(t.dat) as maxdatetime,
min(t.dat) as mindatetime
into
temptable
from
list_of_dates t
group by
t.number
To generate a temporary table called temptable, then run the following update query which sources date from this temporary table:
update
list_of_things t1 inner join temptable t2
on t1.number = t2.number
set
t1.latest = t2.maxdatetime,
t1.earliest = t2.mindatetime
2. Use Domain Aggregate Functions
Since domain aggregate functions (dcount, dsum, dmin, dmax etc.) are evaluated separately from the evaluation of the query, they do not break the updateable nature of a query.
As such, you might consider using a query such as:
update
list_of_things t1
set
t1.latest = dmax("dat","list_of_dates","number = " & t1.number),
t1.earliest = dmin("dat","list_of_dates","number = " & t1.number)
It's a shot in the dark, but try adding DistinctRow as per SQL Update woes in MS Access - Operation must use an updateable query
Also try using an inner join. If you need to, you can run an update to a null value first for all the records in the query to simulate the effect of the outer join.
I have the following query:
select x.id0
from (
select *
from sessions
inner join clicked_products on sessions.id0 = clicked_products.session_id0
) x;
Since id0 is in both sessions and clicked_products, I get the expected error:
column reference "id0" is ambiguous
However, to fix this problem in the past I simply needed to specify a table. In this situation, I tried:
select sessions.id0
from (
select *
from sessions
inner join clicked_products on sessions.id0 = clicked_products.session_id0
) x;
However, this results in the following error:
missing FROM-clause entry for table "sessions"
How do I return just the id0 column from the above query?
Note: I realize I can trivially solve the problem by getting rid of the subquery all together:
select sessions.id0
from sessions
inner join clicked_products on sessions.id0 = clicked_products.session_id0;
However, I need to do further aggregations and so do need to keep the subquery syntax.
The only way you can do that is by using aliases for the columns returned from the subquery so that the names are no longer ambiguous.
Qualifying the column with the table name does not work, because sessions is not visible at that point (only x is).
True, this way you cannot use SELECT *, but you shouldn't do that anyway. For a reason why, your query is a wonderful example:
Imagine that you have a query like yours that works, and then somebody adds a new column with the same name as a column in the other table. Then your query suddenly and mysteriously breaks.
Avoid SELECT *. It is ok for ad-hoc queries, but not in code.
select x.id from
(select sessions.id0 as id, clicked_products.* from sessions
inner join
clicked_products on
sessions.id0 = clicked_products.session_id0 ) x;
However, you have to specify other columns from the table sessions since you cannot use SELECT *
I assume:
select x.id from (select sessions.id0 id
from sessions
inner join clicked_products
on sessions.id0 = clicked_products.session_id0 ) x;
should work.
Other option is to use Common Table Expression which are more readable and easier to test.
But still need alias or selecting unique column names.
In general selecting everything with * is not a good idea -- reading all columns is waste of IO.
I would like to update columns in Table A based on values in Table B. Using below format, but getting syntax error.
update TableA
set
TableA.MOdule_id =TableB.MOdule_id
from TableA
inner join
TableB
on TableA.end_Slot_id =TableB.Slot_Id
where TableA.Slot_Id = 'AAA';
It would be great help, if anyone can help on this.
A quick search for "informix sql update" returns two reference manual pages that describe the syntax for the UPDATE command. Neither one indicates support for the nonstandard FROM clause.
Standard SQL uses a correlated subquery for the purpose. Your query should look something like
update TableA
set MOdule_id =
(select TableB.MOdule_id
from TableB
on TableA.end_Slot_id = Slot_Id)
where Slot_Id = 'AAA'
and exists (
select 1
from TableB
on TableA.end_Slot_id = Slot_Id
and TableA.Slot_Id = 'AAA'
);
The EXISTS clause ensures that only rows that exist in B are applied to A. Without it, any missing rows would be updated to NULL.
Platform used:
SQL Server 2008 and C++ Builder
I am doing an inner join between 2 tables which was giving me an error:
Row cannot be located for updating
Query:
SELECT DISTINCT
b.Acc, b.Region, b.Off, b.Sale, a.OrgDate
FROM
sales b
INNER JOIN
dates a ON (a.Acc = b.Acc and a.Region = b.Region and a.year= b.year)
WHERE
(a.xdate <> a.yDate)
and (b.Sale = a.SaleDate)
and b.year = 2010
Note: Acc, Region, Off are primary keys of table b and are also present in table a.
Table a has an id which is the primary key which does not appear in the query.
It turned out that my inner join was returning duplicate rows.
I changed my inner join query to use 'DISTINCT' so that only distinct rows are returned and not duplicate. The query runs but then I get the error:
Insufficient key column information for updating or refreshing.
It does turn out that the fields which are primary keys in Table A have the same names as the fields in Table B
I found that this is a bug which occurs while updating ADO record-sets.
BUG: Problem Updating ADO Hierarchical Recordset When Join Tables Share Same Column Name
I have the following 2 questions:
Is it not a good idea to use Distinct on an inner join query?
Has anyone found a resolution for that bug associated with TADO Query's?
Thank you,
The way I would solve this is to construct an update query by hand and run it through TADOQuery.ExecSQL. That assumes you actually know what you are doing.
The question is WHY are you working on a recordset that results in multiples of the same row, on all fields? You should be inspecting your query and fixing it. DISTINCT doesn't help, because SQL Server has picked one record but ADO won't know which one it picked, since there isn't enough information to properly identify the source on each side of the JOIN.
This query pulls in a.id to make the source records identifiable:
SELECT Acc,Region,Off,Sale,OrgDate,id
FROM
(
SELECT b.Acc,b.Region,b.Off,b.Sale,a.OrgDate, a.id,
rn=row_number() over (partition by b.Acc,b.Region,b.Off order by a.id asc)
FROM sales b
JOIN dates a ON(a.Acc = b.Acc and a.Region = b.Region and a.year= b.year)
WHERE a.xdate <> a.yDate
and b.Sale = a.SaleDate
and b.year = 2010
) X
WHERE rn=1;
Not tested, but it should work with ADO
I was trying to achieve this query1:
UPDATE temp_svn1 t set closedate=(select max(date) from temp_svn1 p where p.id=t.id
Apparently MySQL does not allow such queries. So I came up with this query using inner joins but this is too slow. How can I write a better query for this? OR How can I achieve the logic of query 1?
UPDATE temp_svn1 AS out INNER JOIN (select id, close from temp_svn1 T inner join (select id as cat, max(date) as close from temp_svn1 group by cat) as in where T.id = in.cat group by id ) as result ON out.id = result.id SET out.closedate = result.close
Because of mysql peculiarities the only way you're going to get this to be faster is to split it into two statements. First, fetch the max, and then use it in an update. This is a known hack, and, afaik, there's not a "neater" way of doing it in a single statement.
Since your subquery is just returning a single value, you could do the query in two stages. Select the max(date) into a server-side variable, then re-use that variable in the outer query. Of course, this breaks things up into two queries and it'll no longer be atomic. But with appropriate transactions/locks, that becomes moot.
This works:
UPDATE temp_svn1
set closedate = (select max(date) from temp_svn1 p where p.id = temp_svn1.id)