We Keep Coding

Remove need for second T-SQL query

I am loading some data into a repeater which is coming from two tables. The query against the second table is only selecting the MAX record though, and because of this complexity, I'm having to create a child repeater to then go off and find the Max record to display.
Table A: Activity List
ID | Activity
----+-----------------------
1 | Change Oil Filter
2 | Change brake fluid
3 | Change brake rotors
Table B: Mechanics Log
ID | ActivityID | Date | Mechanic | Comment
---+-------------+-------------+-------------------------------------------
1 | 1 | 2019-27-06 | John | Changed the oil filter
2 | 1 | 2019-26-06 | Sally | No oil filters in stock.
3 | 2 | 2019-20-06 | Sally | Brake fluid flushed.
As stated above, I can produce the following table using two repeaters (one inside the other) and it looks like this.
ActivityID | Date | Mechanic | Comment
-------------+-------------+-----------------------------------------
1 | 2019-27-06 | John | Changed the oil filter
2 | 2019-20-06 | Sally | Brake fluid flushed.
3 | | |
My question is: How can I produce the same table but using only one repeater and 1 T-SQL query? Is it possible? The reason being is that this is a very simple list (shortened for this demonstration) of the full list I have to enable for my mechanics work log, and when i start going to 100+ activities that can be done on a vehicle, the page loads quite slow; assuming because it has to fire off the 2nd repeater + code for each record it has bound.
I also apologize I do not yet have a 'starting point' for you to work with, as nothing I have created has come even close to producing the result in one query. I am having trouble working out how I combine the first part of the query with the MAX(Date) of the 2nd table. Hoping for some assistance from the community to help.

You can use the below query to get the desired result -
Sample Data
Declare #ActivityList Table
(ID int, Activity varchar(100))
Insert into #ActivityList
values
(1 , 'Change Oil Filter' ),
(2 , 'Change brake fluid' ),
(3 , 'Change brake rotors' )
Declare #MechanicsLog Table
(ID int, ActivityID int, [Date] Date, Mechanic varchar(20), Comment varchar(50))
Insert into #MechanicsLog
values
(1 , 1 , '2019-06-27' , 'John' , 'Changed the oil filter' ),
(2 , 1 , '2019-06-26' , 'Sally' , 'No oil filters in stock.' ),
(3 , 2 , '2019-06-20' , 'Sally' , 'Brake fluid flushed.' )
Query
;With cte as
(select ActivityID, Max([Date]) [date] from #MechanicsLog ml
Group By ActivityID
)
Select al.ID, al.Activity, cte.[Date], Mechanic, Comment
from cte inner join #MechanicsLog ml
on cte.ActivityID = ml.ActivityID and cte.[date] = ml.[Date]
right join #ActivityList al on al.ID = ml.ActivityID
order by ID

If you add use the ROW_NUMBER function to add a sequence to each activity ID, you can then filter that to only get the most recent for each activity ID.
select ActivityID, Date, Mechanic, Comment
from
(
select *, ROW_NUMBER() OVER (PARTITION BY ActivityID order by Date desc) RowNumber
from MechanicsLog
) q1
where RowNumber = 1
This gives you the "MAX" record for each ActivityID but with the rest of the record, so you can join to the Activity List table if you want.

select
act.ActivityID, Max(log.[Date]) as [Date]
from
ActivityList act
inner join
MachineLog log on log.ActivityID = act.ActivityID
Group by
act.ActivityID

TSQL Transpose a column of a table into a row

I have a temporary table with one column containing 3 pieces of data: Code, Date, and Quantity.
Example:
-------
FR123456
24/02/1988
500
I need to extract the data in this column into separate columns.
Example:
Code | Date | Quantity
--------- ----------- ----
FR123456 | 24/02/1988 | 500
I used this code:
SELECT [1], [2], [3]
FROM
(
SELECT row_number() OVER (ORDER BY splitdata DESC) AS Id, splitdata
FROM splitdata
) AS SourceTable
PIVOT
(
MIN (splitdata)
FOR id IN ([1], [2], [3])
) AS PivotTable;
The problem with it is that once the content of data changes, I may get the quantity content into the date column due to the aggregate function (MIN).

I assume this is SQL-Server related...
Your problem is: A SQL-Server table does not have any kind of implicit sort order. A simple SELECT * FROM SomeWhere can return in the sort order you've inserted your data, but can return completely different as well. The only chance to ensure a sort order is an ORDER BY at the outer-most query against a (set of) unique column(s).
You can create a sort order by kind of analysing your data:
This is a mockup-table with your test data:
DECLARE #mockup TABLE(YourColumn VARCHAR(100));
INSERT INTO #mockup VALUES
('FR123456')
,('24/02/1988')
,('500');
--The query will check the values if they can be casted to a number, to a date or not.
--This will be used to place a sort order to the values.
--I use 105 in CONVERT to enforce the dateformat dd-MM-yyyy
SELECT CASE WHEN TRY_CONVERT(DATE,YourColumn,105) IS NOT NULL THEN 2
ELSE CASE WHEN TRY_CAST(YourColumn AS INT) IS NOT NULL THEN 3 ELSE 1
END
END AS SortOrder
,YourColumn
FROM #mockup
ORDER BY SortOrder;
But if there are several triplets in your table, not just one as in your sample, I'm afraid you're lost...
Btw: Your own approach tries to do exactly the same:
SELECT row_number() OVER (order by splitdata desc)as Id
This will create kind of a sort order number, but it will be random (a quantity will appeare before or after the date depending on alphanumerical rules).
Hint
Add an IDENTITY column to your table. This will use an increasing number for any row the moment it is created. These values can be used to enforce the order as inserted (by using ORDER BY with this column).
UPDATE: Your query
SELECT [1], [2] , [3]
FROM
(SELECT CASE WHEN TRY_CONVERT(DATE,splitdata,105) IS NOT NULL THEN 2
ELSE CASE WHEN TRY_CAST(splitdata AS INT) IS NOT NULL THEN 3 ELSE 1
END
END AS Id , splitdata
from #mockup ) AS SourceTable
PIVOT
(
MIN (splitdata)
FOR id IN ([1], [2], [3])
) AS PivotTable;

Faster way to insert records into database

So I currently have a database table of about 70,000 names. What I want to do is take 3000 random records from that database and insert them into another table where each name has a row for all the other names. In other words, the new table should look like this:
John, jerry
john, alex
john, sam
jerry, alex
jerry, sam
alex, sam
This means that I should be adding summation n rows to the table. My current strategy is to use two nested for loops to add these rows one at a time and then removing the first name from the list of names to add in order to ensure I dont have a duplicate record with different ordering.
My question is this: is there a faster way to do this, perhaps through parallel for loops or PLINQ or some other option that I a have not mentioned?

Given a table "Names" with an nvarchar(50) column "Name" with this data:
Adam
Bob
Charlie
Den
Eric
Fred
This query:
-- Work out the fraction we need
DECLARE #frac AS float;
SELECT #frac = CAST(35000 AS float) / 70000;
-- Get roughly that sample size
WITH ts AS (
SELECT Name FROM Names
WHERE #frac >= CAST(CHECKSUM(NEWID(), Name) & 0x7FFFFFFF AS float) / CAST (0X7FFFFFFF AS int)
)
-- Match each entry in the sample with all the other entries
SELECT x.Name + ', ' + y.Name
FROM ts AS X
CROSS JOIN
Names AS Y
WHERE x.Name <> y.Name
produces results of the form
Adam, Bob
Adam, Charlie
Adam, Den
Adam, Eric
Adam, Fred
Charlie, Adam
Charlie, Bob
Charlie, Den
Charlie, Eric
Charlie, Fred
Den, Adam
Den, Bob
Den, Charlie
Den, Eric
Den, Fred
The results will vary by run; a sample of 3000 out of 70000 will have approximately 3000 * 70000 result rows. I used 35000./70000 because the sample size I used was only 6.
If you want only the names from the sample used, change CROSS JOIN Names AS Y to CROSS JOIN ts AS Y, and there will then be approximately 3000 * 3000 result rows.
Reference: The random sample method was taken from the section "Important" in Limiting Result Sets by Using TABLESAMPLE.

You will need to figure out the random part
select t1.name, t2.name
from table t1
join table t2
on t1.name < t2.name
order by t1.name, t2.name
You need to materialize the newid
declare #t table (name varchar(10) primary key);
insert into #t (name) values
('Adam')
, ('Bob')
, ('Charlie')
, ('Den')
, ('Eric')
, ('Fred');
declare #top table (name varchar(10) primary key);
insert into #top (name)
select top (4) name from #t order by NEWID();
select * from #top;
select a.name, b.name
from #top a
join #top b
on a.name < b.name
order by a.name, b.name;

Using a Number table to simulate names.
single query, using a triangular join
WITH all_names
AS (SELECT n,
'NAME_' + Cast(n AS VARCHAR(20)) NAME
FROM number
WHERE n < 70000),
rand_names
AS (SELECT TOP 3000 *
FROM all_names
ORDER BY Newid()),
ordered_names
AS (SELECT Row_number()
OVER (
ORDER BY NAME) rw_num,
NAME
FROM rand_names)
SELECT n1.NAME,
n2.NAME
FROM ordered_names n1
INNER JOIN ordered_names n2
ON n2.rw_num > n1.rw_num

Update table column based on comparison of columns from 2 table (SQL)

I have the following tables.
Table 1
Id | Values | Counts
1 | rock | 0
2 | tina | 0
3 | alex | 0
Table 2
Id | Values
1 | rock
2 | alex
3 | alex
4 | rock
5 | rock
6 | tina
As you can see, table 1 contains Values as rock, tina and alex. These column will always have unique values. Counts column should check the count of 'rock' in Table 2 and update it in Counts column. for e.g. rock is shown 3 times in table 2. The counts for rock should be then 3.
Similarly for other values. Can someone pls let me know how can i achieve this using SQL. Here is how the final table should look like.
Table 1
Id | Values | Counts
1 | rock | 3
2 | tina | 1
3 | alex | 2
Any help is appreciated. I searched online and couldnot find a possible solution for this scenario.

You can generally use a JOIN between 2 tables to update Table1 with values from Table2 (or further if you are using bridge tables).
UPDATE t1
SET t1.dataColumn = t2.dataColumn
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.keyColumn = t2.keyColumn
However, when you are using Aggregate functions (such as Count, Sum)you must utilize a subquery for the second table and perform the JOIN to that subquery
UPDATE t1
SET t1.Counts = sb.Counts
FROM Table1 AS t1
INNER JOIN (
SELECT [values], Counts = Count([values])
FROM Table2
GROUP BY [values]
) AS sb
ON t1.[values] = sb.[values]
Running this on your tables gave me this:
SELECT * FROM Table1
id values counts
---- ------- -------
1 rock 3
2 tina 1
3 alex 2
One thing concerning your table design; I generally recommend not using reserved/special/key words when naming tables, columns, or other database objects. I also try to avoid using the generic name id because it can get confusing when you start linking tables to one another, even idTable1 can make things a lot easier

In SQL Server, using a correlated subquery:
update t1
set t1.Counts = (
select count(*)
from t2
where t2.[Values] = t1.[Values]
);
rextester demo: http://rextester.com/SBYNB72372
In MySQL, using a correlated subquery:
update t1
set t1.Counts = (
select count(*)
from t2
where t2.`Values` = t1.`Values`
);
rextester demo: http://rextester.com/DDDC21719
Although this sort of thing might be better calculated in a view instead of stored in the t1 table.
In SQL Server:
create view dbo.t1_with_counts as
select t1.Id, t1.[Values], count(t2.[Values]) as Counts
from t1
left join t2
on t1.[Values] = t2.[Values]
group by t1.Id, t1.[Values]
go
select *
from dbo.t1_with_counts;
In MySQL:
create view t1_with_counts as
select t1.Id, t1.`Values`, count(t2.`Values`) as Counts
from t1
left join t2
on t1.`Values` = t2.`Values`
group by t1.Id, t1.`Values`;
select *
from t1_with_counts;

I would question the wisdom of keeping track of a count in a table like that. That leads to poor relational database structure and management. Instead, I suggest you remove the count column from Table 1. Then, whenever you need to see the counts you use a view:
SELECT t1.ID, t1.VALUES, COUNT(t2.ID) AS VALUE_COUNT
FROM TABLE1 t1 LEFT JOIN TABLE2 t2 ON t1.VALUES = t2.VALUES
This results in a dynamically updated view of your data instead of a static view that has the potential for going stale without your realizing it.

Correctly generating a unique invoice id

I've been asked to clean up someone else's controller code, which generates an invoice, and I've run into something I don't know how to fix. The code in question is as follows (this is using EF 6: Code First):
var invid = db.TransportJobInvoice.Where(c => c.CompanyId == CompanyId)
.Max(i => i.InvoiceId);
var invoiceId = invid == null ? 1 : (int)invid + 1;
The code is supposed to generate an invoiceId based on the company the invoice is being created for. So a small table of this might look as follows:
------------------------------
| Id | CompanyId | InvoiceId |
------------------------------
| 1 | 1 | 1 |
------------------------------
| 2 | 1 | 2 |
------------------------------
| 3 | 1 | 3 |
------------------------------
| 4 | 2 | 1 |
------------------------------
| 5 | 2 | 2 |
------------------------------
As you can see, the invoiceId would be generated based on the current number of invoices for the company in question. However, I think it's reasonable to suggest that two threads could execute the query before this line is evaluated:
var invoiceId = invid == null ? 1 : (int)invid + 1;
which would result in the same invoiceId being generated for two different invoices.
Is there a simple solution to this, possibly leveraging Entity Framework to do this automatically?

I suggest using the identity for the primary key, very important!
I would then add a column for "CustomerInvoiceID" and put a compound unique key on CustomerID and CustomerInvoiceID".
Then, create a stored procedure that will populate the field CustomerInvoiceID after it has been inserted, here is some pseudo code:
CREATE PROCEDURE usp_PopulateCustomerInvoiceID
#PrimaryKey INT, --this is your primary key identity column
#CustomerID INT
AS
BEGIN
SET NOCOUNT ON;
DECLARE #cnt INT;
SELECT #CNT = COUNT(1)
FROM TBL
WHERE CustomerID = #CustomerID
AND PrimaryKeyColumn <= #PrimaryKey
UPDATE tbl
SET CustomerInvoiceID = #cnt + 1
WHERE PrimaryKeyColumn = #PrimaryKey
END

Two possibilities:
Server-side: Don't compute the max(ID)+1 on the client. Instead, as part of the INSERT statement, compute the max(ID)+1, via an INSERT..SELECT statement.
Client-side: Instead of an incrementing int, generate a GUID on the client, and use that as your InvoiceID.

A rather different approach would be to create a separate table with the NextId for each CustomerId. As new customers are added you would add a new row to this table. It has the advantage that the numbers assigned to invoices can remain unique even if you allow deleting invoices.
create procedure GetInvoiceIdForCustomer
#CustomerId as Int,
#InvoiceId as Int Output
as
begin
set nocount on
begin transaction
update CustomerInvoiceNumbers
set #InvoiceId = NextId, NextId += 1
where CustomerId = #CustomerId
if ##RowCount = 0
begin
set #InvoiceId = 1
insert into CustomerInvoiceNumbers ( CustomerId, NextId ) values ( #CustomerId, #InvoiceId + 1 )
end
commit transaction
end
end

If you use an Identity field in SQL Server, this will be handled automatically.

I don't know if you can make the invoice id auto generated unless it's beinng threated as a foreign key (which I think it isn't).
You problem with multiple threads could be solved using a lock statement.
lock (myLock)
{
var invid = db.TransportJobInvoice.Where(c => c.CompanyId == CompanyId)
.Max(i => i.InvoiceId);
var invoiceId = invid == null ? 1 : (int)invid + 1;
}
This will guarantee that only thread is executing these statements.
Be careful though, this could cause performance issues when those statements are executed alot in parallel and the query takes some significant time to execute.