I'd like to select top {n} rows from sql-server
SELECT TOP 10 * FROM CUSTOMER; --> n should be configurable
How can I do this using JDBC?
Should I write a prepared statement and supply ? instead of 10?
Or Should I construct the SQL string and execute it as normal statement?
I just want to know if there's a de facto choice of supplying dynamic FETCH LIMIT (a configured value usually)
I suggest to use Pageable with JPA like this refer to https://www.baeldung.com/jpa-limit-query-results
Page<Passenger> page = repository.findAll(PageRequest.of(0, 1, Sort.by(Sort.Direction.ASC, "seatNumber")));
Related
I work with large databases that needs to be stored into a server.
So, to work with them on Rstudio I have to open a connection to my Microsoft SQL Server with the dbConnect function :
conn <- dbConnect(odbc(),"myconnection",uid="***",pwd="***",schema="dbo",access="readonly")
and in order to use dplyr, I have to create data references with the tbl function :
data <- tbl(conn, "data")
But one of the online dataframe contains a columns that I can't read because I dont have the access, but I can read everything else.
The SQL query behind the tbl() function is :
SELECT * FROM data
and this is my problem.
Even when I try to select a specific column it doesn't work (see below), so I can't create my references and I can't work.
select(tbl(conn, "data"), "columnX")
=
SELECT columnX FROM data
I think this is the tbl() function and the call of "SELECT *" that blocks me.
Do you know what can I do ? Is there smilar functions that could resolve my problem ?
If you know the columns that you have access to, then one option is to bypass the default access SELECT * FROM ... with your own SQL query.
A remote table is defined by two components:
The database conneciton
The query to the database
When you connect with the default approach tbl(conn, 'data') then it defaults to a query SELECT * FROM data.
But here is another approach:
custom_query = 'SELECT columnX FROM data'
remote_table = tbl(conn, dbplyr::sql(customer_query))
I'm working on a project that has a search engine. AS we know in MS ACCESS we could use "*" in Queries under Criteria field to retrieve all records.
In SQL Server I need the same technique. I have tried different LIKE with WHERE Clauses. But I still didn't get the exact result I want.
In this project I have 3 textboxes (Category, Item, Location). If the user leaves any of them empty. I want to retrieve all the records.
I need something like this:
string t1,t2,t3;
if(!String.IsNullOrEmpty(txtCategory.Text))
t1=txtCategory.Text;
else
t1="*";
if(!String.IsNullOrEmpty(txtItem.Text))
t2=txtItem.Text;
else
t2="*"
if(!String.IsNullOrEmpty(txtLoc.Text))
t2=txtLoc.Text;
else
t3="*";
-
-
-
// in a function i have this :
SELECT * FROM Table_Items WHERE Category='"+t1+"' AND Item='"+t2+"' AND Location='"+t3+"'"
in ms sql server you can use the same technique but instead of * you should use %.
for examples:
%: means any
a%: all strings that start with a
%z: all strings that end with z
SO, your code should look like something as below:
// codes here
t3="%";
WHERE ColumnName LIKE t3
or
Where ColumnName LIKE '%'
I hope that will help you.
Change your * to the %
... Where Category Like "'+t1+"' and Item Like '"+t2+"' ...
Using SQL Server Management
Using MVC VS 2013 for Web
Being in a Controller
Here materialnumb it's a LINQ query that always return only one value.
Being the following...
var materialnumb = (from r in db.MaterialNumber
where r.MaterialNumber == 80254842
select r.MaterialNumber);
I have another LINQ query from a SQL view that involves several other tables with inner join statements and so on (which includes the previous table db.MaterialNumber) that goes like this:
var query = (from r in db.SQLViewFinalTable
where r.MaterialNumber == Convert.ToInt32(materialnumb.MaterialNumber)
select r
I want to sort all the materials by the retrieved material number from the first query but it drops the following error when I try to pass the query as a model for my View:
LINQ to Entities does not recognize the method 'Int32
ToInt32(System.String)' method, and this method cannot be translated
into a store expression.
I assume this is because the query is an object even if its has just one value so it can't be converted into a single Int32.
Even more, the query it's not being executed, it's just a query...
So, how can achieve my goal?
Additional information: I tried to convert the query outside the "final" query. It still doesn't work.
Additional information: This is just an example, the true query actually has several more other querys embedded and this other querys have also other querys in them, so I need a practical way.
Additional information: I have also tried to convert the query into a string and then again into an int.
Try this:
var materialnumb = (from r in db.MaterialNumber
where r.MaterialNumber == 80254842
select r.MaterialNumber).FirstOrDefault();
var query = from r in db.SQLViewFinalTable
where r.MaterialNumber == materialnumb
select r
But I can not get whay are you filtering by 80254842 and selecting the same value? You can do directly:
var query = from r in db.SQLViewFinalTable
where r.MaterialNumber == 80254842
select r
I have an entity framework query that has this at the heart of it:
SELECT 1 AS dummy
FROM [dbo].[WidgetOrder] AS widgets
WHERE widgets.[SomeOtherOrderId] = N'SOME VALUE HERE'
The execution plan for this chooses an index that is a composite of three columns. This takes 10 to 12 seconds.
However, there is an index that is just [SomeOtherOrderId] with a few other columns in the "include". That is the index that should be used. And when I run the following queries it is used:
SELECT 1 AS dummy
FROM [dbo].[WidgetOrder] AS widgets
WHERE widgets.[SomeOtherOrderId] = CAST(N'SOME VALUE HERE' AS VARCHAR(200))
SELECT 1 AS dummy
FROM [dbo].[WidgetOrder] AS widgets
WHERE widgets.[SomeOtherOrderId] = 'SOME VALUE HERE'
This returns instantly. And it uses the index that is just SomeOtherOrderId
So, my problem is that I can't really change how Entity Framework makes the query.
Is there something I can do from an indexing point of view that could cause the correct index to be selected?
As far as I know, since version 4.0, EF doesn't generate unicode parameters for non-unicode columns. But you can always force non-unicode parameters by DbFunctions.AsNonUnicode (prior to EF6, DbFunctions is EntityFunctions):
from o in db.WidgetOrder
where o.SomeOtherOrderId == DbFunctions.AsNonUnicode(param)
select o
Try something like ....
SELECT 1 AS dummy
FROM [dbo].[WidgetOrder] AS widgets WITH (INDEX(Target_Index_Name))
WHERE widgets.[SomeOtherOrderId] = N'SOME VALUE HERE'
This query hint sql server explicitly what index to use to get resutls.
Say you have a stored procedure or function returning multiple rows, as discussed in How to return multiple rows from the stored procedure? (Oracle PL/SQL)
What would be a good way, using Scala, to "select * from table (all_emps);" (taken from URL above) and read the multiple rows of data that would be the result?
As far as I can see it is not possible to do this using Squeryl. Is there a scalaified tool like Squeryl that I can use, or do I have to drop to JDBC?
Functions that return tables are an Oracle specific feature, I doubt an ORM (be it Scala or even Java) would have support for such a proprietary extension.
So I think you're more or less on your own :).
Probably the easiest way is to use a plain JDBC java.sql.Statement and execute "select * from table (all_emps)" with the executeQuery method.
To address the second part of your question about a way to select from table in a more scala-esque way, I am using Slick. Quoting from their example documentation:
case class Coffee(name: String, supID: Int, price: Double)
implicit val getCoffeeResult = GetResult(r => Coffee(r.<<, r.<<, r.<<))
Database.forURL("...") withSession {
Seq(
Coffee("Colombian", 101, 7.99),
Coffee("Colombian_Decaf", 101, 8.99),
Coffee("French_Roast_Decaf", 49, 9.99)
).foreach(c => sqlu"""
insert into coffees values (${c.name}, ${c.supID}, ${c.price})
""").execute)
val sup = 101
val q = sql"select * from coffees where sup_id = $sup".as[Coffee]
// A bind variable to prevent SQL injection ^
q.foreach(println)
}
Though I am not sure how it's dealing (if at all) with stored procs/functions.