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Linq into clause returning only columns from joined table

I joined a 2 data tables based on the EMP column and used copytodatatable, however when i load the new datatable into datagridview it only shows the joined columns(salarydt) from the query, why is this??
var collection = from p in dt.AsEnumerable()
join q in salaryDT.AsEnumerable() on p.Field<int>("Emp") equals q.Field<int>("Emp1") into UP
from t in UP
select t;
DataTable resultdt = new DataTable();
dt = collection.CopyToDataTable();

DataTable itself is perfectly geared to merging itself with another data table, using its, well, Merge method. Here's a litte example:
var dt1 = new DataTable("a");
dt1.Columns.Add("ID", typeof(int));
dt1.Columns.Add("Item1", typeof(int));
dt1.PrimaryKey = new[] { dt1.Columns[0] };
var dt2 = new DataTable("a");
dt2.Columns.Add("ID", typeof(int));
dt2.Columns.Add("Item2", typeof(int));
dt2.PrimaryKey = new[] { dt2.Columns[0] };
for (int i = 0; i < 10; i++)
{
dt1.Rows.Add(new object[] { i, i });
dt2.Rows.Add(new object[] { i, i + 10 });
}
dt1.Merge(dt2);
Now dt1 has three columns, ID, Item1, and Item2.
ID Item1 Item2
0 0 10
1 1 11
2 2 12
3 3 13
4 4 14
5 5 15
6 6 16
7 7 17
8 8 18
9 9 19

Maybe what you should to do is just return a custom list of items:
Option 1
var data = new Employee[] { new Employee { Id = 1, Name = "John Doe" } };
var data2 = new Salary[] { new Salary { Id = 1, Wage = "$ 50,000.00" } };
var collection = from p in data
join q in data2 on p.Id equals q.Id
select new { Id = p.Id, Name = p.Name, Wage = q.Wage };
Please check the example: link
Option 2
var data = new Employee[] { new Employee { Id = 1, Name = "John Doe" } };
var data2 = new Salary[] { new Salary { Id = 1, Wage = "$ 50,000.00" } };
var collection = from p in data
join q in data2 on p.Id equals q.Id
select new { p, q };

How to loop and update SQL table summing any existing values

Please i need your help on this module part of my program. i have 2 tables, TableA which has "code,description,value" and TableB which has "code, values" example below :
TableA
code description value
-----------------------------
CD1 BOOKS
CD2 BREADS
CD3 PHONES
CD4 FISH
TableB
code value1 value2 value3 value4
--------------------------------------
cd1 12 21 10 21
cd2 9 10 10 11
cd3 19 11 29 13
cd4 10 12 22 12
the idea is to update TableA with the Values of TableB where TableA.code=TableB.code but if their are values in TableA then Update content of TableA Value field by adding the new values to the old value field where TableB.code = TableA.code. i have written the following code but it's only updating one row, below is my code :
DataTable dt = GetDatafromDatabase(); //===== returns a DataTable
string SQLT = "SELECT * FROM tbl_TempReport";
if (cn.State == ConnectionState.Closed) {cn.Open(); }
SqlCommand cmdT = new SqlCommand(SQLT, cn);
while (rt.Read())
{
// For each row, print the values of each column.
foreach (DataColumn column in dt.Columns)
{
foreach (DataRow row in dt.Rows)
{
colname = column.ColumnName.ToString();
string m_Code = rt["code"].ToString();
if (m_Code == colname) {
if (m_Code == colname && mValue > 0) { mValue += Convert.ToInt32(row[column].ToString()); } else { mValue = Convert.ToInt32(row[column].ToString()); }
//============ insert into tbl_TempReport to match the appropriate column
string SQLP = "UPDATE tbl_TempReport SET VALUEP = #VALUEP WHERE code = #code";
SqlCommand cmdp = new SqlCommand(SQLP, cn);
cmdp.Parameters.AddWithValue("#VALUEP", SqlDbType.Int).Value = mValue;
cmdp.Parameters.AddWithValue("#code", SqlDbType.NVarChar).Value = rt["code"].ToString();
cmdp.ExecuteNonQuery();
}
}
}
}
i need your help to achieve this. Thank you

If I understand the question, this can be done in a single update statement, without any loops:
UPDATE a
SET value = b.value1 + b.value2 + b.value3 + b.value4 + COALESCE(value, 0)
FROM TableA a
INNER JOIN TableB b ON(a.code = b.code)

Datatable Group by and sum one column

I have this datatable:
RadkyData.Columns.Add("ČísloDokladuDodavatele", typeof(string));
RadkyData.Columns.Add("Množství", typeof(string));
RadkyData.Columns.Add("NákupníCena", typeof(string));
RadkyData.Columns.Add("PřepočtováJednotka", typeof(string));
RadkyData.Columns.Add("Přepočtovýkoeficient",

Just group the rows by Col1, Col2,Col3 and Sum() up Col4
var input = new[] {
new { Col1 =1, Col2= 2, Col3 = 1, Col4 = 1.5m},
new { Col1 =1, Col2= 1, Col3 = 1, Col4 = 1.8m},
new { Col1 =1, Col2= 2, Col3 = 1, Col4 = 2.5m},
new { Col1 =1, Col2 =1, Col3 = 1, Col4 = 3m},
new { Col1 =3, Col2 =1, Col3 = 4, Col4= 5m}
};
var result = input.GroupBy(x => new { x.Col1, x.Col2, x.Col3 })
.Select(x => new
{
Col1 = x.Key.Col1,
Col2 = x.Key.Col2,
Col3 = x.Key.Col3,
Col4 = x.Sum(y => y.Col4)
});

You could do this using Linq.
table.AsEnumerable()
.Select(r=>new
{
c1=r.Field<int>("col1"),
c2 =r.Field<int>("col2"),
c3 =r.Field<int>("col3"),
c4 =r.Field<double>("col4")
})
.GroupBy(g=> new {g.c1, g.c2, g.c3})
.Select(x=> new {
col1 = x.Key.c1,
col2 = x.Key.c2,
col3 = x.Key.c3,
Sum = x.Sum(s=>s.c4)
});
Check this Demo
Output:
{ col1 = 1, col2 = 2, col3 = 1, Sum = 4 }
{ col1 = 1, col2 = 1, col3 = 1, Sum = 4.8 }
{ col1 = 3, col2 = 1, col3 = 4, Sum = 5 }

I think this should work
mytable.Columns.Add("col4",GetType(Integer),"Col1+Col2+Col3");

SELECT all columns in addition to some summary columns using LINQ

Suppose there is a table with more than 20 columns: (col1, col2, ... )
If I want to display the sum of col1 and col2 as well as the other columns,
In SQL I could:
SELECT (col1+col2), * FROM table1;
But in LINQ, I have to
from tb in table1
select new
{
sum = tb.col1 + tb.col2,
col1 = tb.col1,
col2 = tb.col2,
...
};
Is there another simpler ways? Thanks.

You can extend type of tb entity by sum property and write something like:
table1
.Select(tb => new
{
Tb = tb,
Sum = tb.col1 + tb.col2
})
.Select(x =>
{
x.Tb.sum = x.Sum;
return x.Tb;
});

DataTable group the result

I want to group in Datatable by Name, LastName and the rest should be in same row. Can someone help me with it?
My DataTable:
Name LastName 1 3 2
kiki ha FF
lola mi AA
ka xe UU
kiki ha SS
I want to have DataTable group by Name:
Name LastName 1 3 2
kiki ha FF SS
lola mi AA
ka xe UU
My new code:
var result11 = from t1 in newtable.AsEnumerable()
group t1 by new { Name = t1.Field<String>("Name"), LastName = t1.Field<String>("LastName") } into grp
select new
{
Name = grp.Key.Name,
LastName = grp.Key.LastName,
//Something must be there
};

Add these lines instead of the comment (//something must be there):
C1 = String.Join(",", grp.Select(r=>r.Field<String>("1"))),
C2 = String.Join(",", grp.Select(r=>r.Field<String>("2"))),
C3 = String.Join(",", grp.Select(r=>r.Field<String>("3")))
to get three new columns on the output that aggregate values from the columns 1, 3 and 2.
If you have multiple values in one of the columns for a group, all the values will be shown and separated by comma (,).
If you are sure that there's at most one value per column per group, then you can simply do:
C1 = grp.Max(r => r.Field<String>("1")),
C3 = grp.Max(r => r.Field<String>("3")),
C2 = grp.Max(r => r.Field<String>("2"))

If you want a DataTable as result, this gives your desired result:
var lastNameGroups = from row in table1.AsEnumerable()
group row by new {
Name= row.Field<String>("Name"),
LastName = row.Field<String>("LastName")
} into LastNameGroups
select LastNameGroups;
var table2 = table1.Clone();
foreach (var lng in lastNameGroups)
{
var row = table2.Rows.Add();
row.SetField("Name", lng.Key.Name);
row.SetField("LastName", lng.Key.LastName);
var ones = lng.Where(r => !string.IsNullOrEmpty(r.Field<String>("1")));
if(ones.Any())
row.SetField("1", ones.First().Field<String>("1"));
var twos = lng.Where(r => !string.IsNullOrEmpty(r.Field<String>("2")));
if (twos.Any())
row.SetField("2", twos.First().Field<String>("2"));
var threes = lng.Where(r => !string.IsNullOrEmpty(r.Field<String>("3")));
if (threes.Any())
row.SetField("3", threes.First().Field<String>("3"));
}