I am having problems using spring jpa using a Distinct. My goal it's to return the whole object, instead just the field that pass to "Distinct".
Example:
This is my table:
And I want to Distinct the "Test_ID" where FLOW_ID = 345
So I am doing this:
Page findTestIdDistinctByFlowId(Pageable pageable, String FlowID);
Instead of this (my goal):
Any advice? Another option?
Distinct doesn't apply on a column or select expression it operates on a row in SQL or an entity in JPA.
Since the returned IDs differ the rows are not distinct and get all returned.
I suspect you could achieve what you want with an explicitly written SQL or JPQL statement. But I'm not at all clear what the actual criteria is that you want to use.
Related
How to avoid a column if it contains null without mentioning its name
select * from
ExmGp a
inner join
ExmMstr b
on a.ETID = b.EID
inner join
ExmMrkntry c
on b.AcYear = c.Acyear
I am trying to join three different tables like the above code but in result some of the columns are null. is it possible to avoid them using where condition?
thanks in advance
No, but it is important that you understand the reason why.
The WHERE clause filters rows out of the result set not columns. So, what you are asking is not supported by WHERE or anything else.
Importantly, a SQL query returns data in a tabular format. This format specifies the columns in the result set. These columns cannot be dynamic; they are fixed for the query (unless you construct a string to execute the query).
So, you are "stuck" with all the columns specified in the SELECT. I would recommend that you list each of the columns that you want rather than using SELECT *.
No there is no built-in language construct in TSQL to directly check for NULLs anywhere in the row. There are a number of workarounds though.
See this question for possible solutions
How to count in SQL all fields with null values in one record?
Assume value is an int and the following query is valid:
SELECT blah
FROM table
WHERE attribute = value
Though MAX(expression) returns int, the following is not valid:
SELECT blah
FROM table
WHERE attribute = MAX(expression)
OF course the desired effect can be achieved using a subquery, but my question is why was SQL designed this way - is there some reason why this sort of thing is not allowed? Students coming from programming languages where you can always replace a data-type by a function call that returns that type find this issue confusing. Is there an explanation one can give them rather than just saying "that's the way it is"?
It's just because of the order of operations of a query.
FROM clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause
WHERE just filters the rows returned by FROM. An aggregate function like MAX() can't have a result returned because it hasn't even been applied to anything.
That's also the reason, why you can't use aliases defined in the SELECT clause in a WHERE clause, but you can use aliases defined in FROM clause.
A where clause checks every row to see if it matches the conditions specified.
A max computes a single value from a row set. If you put a max, or any other aggregate function into a where clause, how can SQL server figure out what rows the max function can use until the where clause has finished it filter?
This deals with the order that SQL Server processes commands in. It runs the WHERE clause before a GROUP BY or any aggregate. Since a where clause runs first, SQL Server can't tell if a row will be included in an aggregate until it processes the where. That is what the HAVING clause is for. HAVING runs after the GROUP BY and the WHERE and can include MAX since you have already filtered out the rows you don't want to use. See http://www.bennadel.com/blog/70-SQL-Query-Order-of-Operations.htm for a good explanation of the order in which SQL commands run.
Maybe this work
SELECT blah
FROM table
WHERE attribute = (SELECT MAX(expresion) FROM table1)
The WHERE clause is specifically designed to test conditions against raw data (individual rows of the table). However, MAX is an aggregate function over multiple rows of data. Basically, without a sub-select, the WHERE clause knows nothing about any rows in the table except for the current row. So how can you determine the maximum value over a whole bunch of rows when you don't even know what those rows are?
Yes, it's a little bit of a simplification, especially when dealing with joins, but the same principle applies. WHERE is always row-by-row, so that's all it really knows about.
Even if you have a GROUP BY clause, the WHERE clause still only processes one row at a time in the raw data before grouping. It doesn't know the value of a column in any other rows, so it has no way of knowing which row has the maximum value.
Assuming this is MS SQL Server, the following would work.
SELECT TOP 1 blah
FROM table
ORDER BY expression DESC
I have a pretty straight forward task to query table and filter using some parameter (this parameter is foreign key for other table).
As example Table1 contains following fields:
id, name , description, company_id;
I have a method that takes as input company_id (not company object) and returns all records from table1.
The criteria query looks as follows:
DetachedCriteria criteria = DetachedCriteria.forClass(Table1.class)
.add(Restrictions.eq("company.id", companyId));
The problem is that generated query is too complex because it joins a couple of tables to do this. And this query is not "production ready"
Is there any way to build criteria to have SQL query like this?:
SELECT * from table1 where company_id =?
I suppose you use EAGER instead of LAZY fetch on some your object mapping. If you don't actually need EAGER use LAZY and it should generate more simple query with your DetachedCriteria.
Why is it that in SQL Server I can't do this:
select sum(count(id)) as 'count'
from table
But I can do
select sum(x.count)
from
(
select count(id) as 'count'
from table
) x
Are they not essentially the same thing? How am I meant to be thinking about this in order to understand why the first block of code isn't allowed?
SUM() in your example is a no-op - SUM() of a COUNT() means the same as just COUNT(). So neither of your example queries appear to do anything useful.
It seems to me that nesting aggregates would only make sense if you wanted to apply two different aggregations - meaning GROUP BY on different sets of columns. To specify two different aggregations you would need to use the GROUPING SETS feature or SUM() OVER feature. Maybe if you explain what you want to achieve someone could show you how.
The gist of the issue is that there is no such concept as aggregate of an aggregate applied to a relation, see Aggregation. Having such a concept would leave too many holes in the definition and makes the GROUP BY clause impossible to express: it needs to define both the inner aggregate GROUP BY clause and the outer aggregate as well! This applies also to the other aggregate attributes, like the HAVING clause.
However, the result of an aggregate applied to a relation is another relation, and this result relation in turn can support a new aggregate operator. This explains why you can aggregate the result into an outer SELECT. This leaves no ambiguity in the definition, each SELECT has its own distinct GROUP BY/HAVING clauses.
In simple terms, aggregation functions operate over a column and generate a scalar value, hence they cannot be applied over their result. When you create a select statement over a scalar value you transform it into an artificial column, that's why it can be used by an aggregation function again.
Please note that most of the times there's no point in applying an aggregation function over the result of another aggregation function: in your sample sum(count(id)) == count(id).
i would like to know what your expected result in this sql
select sum(count(id)) as 'count'
from table
when you use the count function, only 1 result(total count) will be return. So, may i ask why you want to sum the only 1 result.
You will surely got the error because an aggregate function cannot perform on an expression containing an aggregate or a subquery.
It's working for me using SQLFiddle, not sure why it would't work for you. But I do have an explanation as to why it might not be working for you and why the alternative would work...
Your example is using a keyword as a column name, that may not always work. But when the column is only in a sub expression, the query engine is free to discard the name (in fact it probaly does) so the fact that it potentially potentially conflicts with a key word may be disregarded.
EDIT: in response to your edit/comment. No, the two aren't equivalent. The RESULT would be equivalent, but the process of getting to that result is not at all similar. For the first to work, the parser has do some work that simply doesn't make sense for it to do (applying an aggregate to a single value, either on a row by row basis or as), in the second case, an aggregate is applied to a table. The fact that the table is a temporary virtual table will be unimportant to the aggregate function.
I think you can write the sql query, which produces 'count' of rows for the required output. Functions do not take aggregated functions like 'sum' or aggregated subquery. My problem was resolved by using a simple sql query to get the count out....
Microsoft SQL Server doesn’t support it.
You can get around this problem by using a Derived table:
select sum(x.count)
from
(
select count(id) as 'count'
from table
) x
On the other hand using the below code will give you an error message.
select sum(count(id)) as 'count'
from table
Cannot perform an aggregate function on an expression containing an
aggregate or a subquery
How can I UPDATE a field of a table with the result of a SELECT query in Microsoft Access 2007.
Here's the Select Query:
SELECT Min(TAX.Tax_Code) AS MinOfTax_Code
FROM TAX, FUNCTIONS
WHERE (((FUNCTIONS.Func_Pure)<=[Tax_ToPrice]) AND ((FUNCTIONS.Func_Year)=[Tax_Year]))
GROUP BY FUNCTIONS.Func_ID;
And here's the Update Query:
UPDATE FUNCTIONS
SET FUNCTIONS.Func_TaxRef = [Result of Select query]
Well, it looks like Access can't do aggregates in UPDATE queries. But it can do aggregates in SELECT queries. So create a query with a definition like:
SELECT func_id, min(tax_code) as MinOfTax_Code
FROM Functions
INNER JOIN Tax
ON (Functions.Func_Year = Tax.Tax_Year)
AND (Functions.Func_Pure <= Tax.Tax_ToPrice)
GROUP BY Func_Id
And save it as YourQuery. Now we have to work around another Access restriction. UPDATE queries can't operate on queries, but they can operate on multiple tables. So let's turn the query into a table with a Make Table query:
SELECT YourQuery.*
INTO MinOfTax_Code
FROM YourQuery
This stores the content of the view in a table called MinOfTax_Code. Now you can do an UPDATE query:
UPDATE MinOfTax_Code
INNER JOIN Functions ON MinOfTax_Code.func_id = Functions.Func_ID
SET Functions.Func_TaxRef = [MinOfTax_Code].[MinOfTax_Code]
Doing SQL in Access is a bit of a stretch, I'd look into Sql Server Express Edition for your project!
I wrote about some of the limitations of correlated subqueries in Access/JET SQL a while back, and noted the syntax for joining multiple tables for SQL UPDATEs. Based on that info and some quick testing, I don't believe there's any way to do what you want with Access/JET in a single SQL UPDATE statement. If you could, the statement would read something like this:
UPDATE FUNCTIONS A
INNER JOIN (
SELECT AA.Func_ID, Min(BB.Tax_Code) AS MinOfTax_Code
FROM TAX BB, FUNCTIONS AA
WHERE AA.Func_Pure<=BB.Tax_ToPrice AND AA.Func_Year= BB.Tax_Year
GROUP BY AA.Func_ID
) B
ON B.Func_ID = A.Func_ID
SET A.Func_TaxRef = B.MinOfTax_Code
Alternatively, Access/JET will sometimes let you get away with saving a subquery as a separate query and then joining it in the UPDATE statement in a more traditional way. So, for instance, if we saved the SELECT subquery above as a separate query named FUNCTIONS_TAX, then the UPDATE statement would be:
UPDATE FUNCTIONS
INNER JOIN FUNCTIONS_TAX
ON FUNCTIONS.Func_ID = FUNCTIONS_TAX.Func_ID
SET FUNCTIONS.Func_TaxRef = FUNCTIONS_TAX.MinOfTax_Code
However, this still doesn't work.
I believe the only way you will make this work is to move the selection and aggregation of the minimum Tax_Code value out-of-band. You could do this with a VBA function, or more easily using the Access DLookup function. Save the GROUP BY subquery above to a separate query named FUNCTIONS_TAX and rewrite the UPDATE statement as:
UPDATE FUNCTIONS
SET Func_TaxRef = DLookup(
"MinOfTax_Code",
"FUNCTIONS_TAX",
"Func_ID = '" & Func_ID & "'"
)
Note that the DLookup function prevents this query from being used outside of Access, for instance via JET OLEDB. Also, the performance of this approach can be pretty terrible depending on how many rows you're targeting, as the subquery is being executed for each FUNCTIONS row (because, of course, it is no longer correlated, which is the whole point in order for it to work).
Good luck!
I had a similar problem. I wanted to find a string in one column and put that value in another column in the same table. The select statement below finds the text inside the parens.
When I created the query in Access I selected all fields. On the SQL view for that query, I replaced the mytable.myfield for the field I wanted to have the value from inside the parens with
SELECT Left(Right(OtherField,Len(OtherField)-InStr((OtherField),"(")),
Len(Right(OtherField,Len(OtherField)-InStr((OtherField),"(")))-1)
I ran a make table query. The make table query has all the fields with the above substitution and ends with INTO NameofNewTable FROM mytable
Does this work? Untested but should get the point across.
UPDATE FUNCTIONS
SET Func_TaxRef =
(
SELECT Min(TAX.Tax_Code) AS MinOfTax_Code
FROM TAX, FUNCTIONS F1
WHERE F1.Func_Pure <= [Tax_ToPrice]
AND F1.Func_Year=[Tax_Year]
AND F1.Func_ID = FUNCTIONS.Func_ID
GROUP BY F1.Func_ID;
)
Basically for each row in FUNCTIONS, the subquery determines the minimum current tax code and sets FUNCTIONS.Func_TaxRef to that value. This is assuming that FUNCTIONS.Func_ID is a Primary or Unique key.
I did want to add one more answer that utilizes a VBA function, but it does get the job done in one SQL statement. Though, it can be slow.
UPDATE FUNCTIONS
SET FUNCTIONS.Func_TaxRef = DLookUp("MinOfTax_Code", "SELECT
FUNCTIONS.Func_ID,Min(TAX.Tax_Code) AS MinOfTax_Code
FROM TAX, FUNCTIONS
WHERE (((FUNCTIONS.Func_Pure)<=[Tax_ToPrice]) AND ((FUNCTIONS.Func_Year)=[Tax_Year]))
GROUP BY FUNCTIONS.Func_ID;", "FUNCTIONS.Func_ID=" & Func_ID)
I know this topic is old, but I thought I could add something to it.
I could not make an Update with Select query work using SQL in MS Access 2010. I used Tomalak's suggestion to make this work. I had a screenshot, but am apparently too much of a newb on this site to be able to post it.
I was able to do this using the Query Design tool, but even as I was looking at a confirmed successful update query, Access was not able to show me the SQL that made it happen. So I could not make this work with SQL code alone.
I created and saved my select query as a separate query. In the Query Design tool, I added the table I'm trying to update the the select query I had saved (I put the unique key in the select query so it had a link between them). Just as Tomalak had suggested, I changed the Query Type to Update. I then just had to choose the fields (and designate the table) I was trying to update. In the "Update To" fields, I typed in the name of the fields from the select query I had brought in.
This format was successful and updated the original table.