write query without using cursors - sql

Question

I wrote this query to display single client's account transactions:
select *
from (
select top 1
[id]
,[client_id]
,[transactionDate]
,N'revolving balance' [details]
,NULL [amount]
,NULL [debit]
,NULL [credit]
,[balance]
FROM [dbo].[bsitems]
where [client_id]=#client_id and
[transactionDate] < #transactionDateFrom
order by id desc) t1
union
SELECT [id]
,[client_id]
,[transactionDate]
,[details]
,[amount]
,[debit]
,[credit]
,[balance]
FROM [dbo].[bsitems]
where [client_id]=#client_id and
[transactionDate] between #transactionDateFrom and #transactionDateTo
How to display the transactions for all clients that exists in "client" table? Assume client table structure is (id, name)

Answer 1

For the second part (which is really what the transactions are), just use join:
SELECT b.id, b.client_id, b.transactionDate, b.details,
b.amount, b.debit, b.credit, b.balance
FROM [dbo].[bsitems] b join
clients c
on b.client_id = c.client_id
WHERE transactionDate between #transactionDateFrom and #transactionDateTo;
This assumes that the client_id is stored in the clients table.
The first part of the query is returning the most recent id before the from date. It returns no rows if there are no previous transactions. You can approach this in a similar way.
select id, client_id, transactiondate, details, amount, debit, credit, balance
from (SELECT b.id, b.client_id, b.transactionDate,
N'revolving balance' as b.details,
NULL as b.amount, NULL as b.debit, NULL as b.credit,
b.balance,
row_number() over (partition by client_id order by TransactionDate desc) as seqnum
FROM [dbo].[bsitems] b join
clients c
on b.client_id = c.client_id
WHERE transactionDate < #transactionDateFrom
) t
where seqnum = 1;
Instead of top 1 this is using row_number() to assign a sequential value to the transactions before the cutoff date. Then the most recent of these is chosen.
The final result is just the union all of these two queries:
select id, client_id, transactiondate, details, amount, debit, credit, balance
from (SELECT b.id, b.client_id, b.transactionDate,
N'revolving balance' as b.details,
NULL as b.amount, NULL as b.debit, NULL as b.credit,
b.balance,
row_number() over (partition by client_id order by TransactionDate desc) as seqnum
FROM [dbo].[bsitems] b join
clients c
on b.client_id = c.client_id
WHERE transactionDate < #transactionDateFrom
) t
where seqnum = 1
union all
SELECT b.id, b.client_id, b.transactionDate, b.details,
b.amount, b.debit, b.credit, b.balance
FROM [dbo].[bsitems] b join
clients c
on b.client_id = c.client_id
WHERE transactionDate between #transactionDateFrom and #transactionDateTo;

Answer 2

SELECT *
FROM (
SELECT TOP 1
[id]
,[client_id]
,[transactionDate]
,N'revolving balance' [details]
,NULL [amount]
,NULL [debit]
,NULL [credit]
,[balance]
FROM [dbo].[bsitems]
INNER JOIN [dbo].[client] ON [dbo].[bsitems].[client_id] = [dbo].[client].[id]
AND [transactionDate] < #transactionDateFrom
ORDER BY id DESC
) t1
UNION
SELECT
[id]
,[client_id]
,[transactionDate]
,[details]
,[amount]
,[debit]
,[credit]
,[balance]
FROM [dbo].[bsitems]
INNER JOIN [dbo].[client] ON [dbo].[bsitems].[client_id] = [dbo].[client].[id]
AND [transactionDate] between #transactionDateFrom and #transactionDateTo