CODEWITHSUNDEEP
sqlsql-servert-sqlwhile-loop
joshi123
joshi123

Reputation: 865

T-SQL date ranges using dynamic variables in loop

I have a table with transactions, timestamps and users. 

CREATE TABLE [dbo].[Transactions]
(
    [transaction_ts] [datetime] NULL,
    [user_id] [bigint] NULL,
    [transaction_id] [bigint] NULL,
    [item] [varchar](50) NULL
)

For each user_id, I need to select all transactions they made between their first transaction and 72 hours later. 

--get first and last timestamps for range
DROP TABLE IF EXISTS #first;

SELECT mt.transaction_ts as first_trans,mt.user_id 
INTO #first
FROM Transactions mt 
INNER JOIN
    (SELECT user_id, MIN(transaction_ts) MinDate
     FROM Transactions
     GROUP BY user_id) t ON mt.user_id = t.user_id AND mt.transaction_ts = t.MinDate;

ALTER TABLE #first
ADD first_trans_plus_72 datetime;

UPDATE #first 
SET first_trans_plus_72 = DATEADD(hour, 72, first_trans)

--loop through user_id and select ranges using variables
DECLARE @Table TABLE (user_id bigint, Id int identity(1,1));

INSERT INTO @Table 
    SELECT DISTINCT user_id 
    FROM #first;

DECLARE @max int;
DECLARE @SQL VARCHAR(MAX);
DECLARE @user_id VARCHAR(max);
DECLARE @first VARCHAR(max);
DECLARE @first_trans_plus_72 VARCHAR(max);
DECLARE @id int = 1;

SELECT @max = MAX(Id) FROM@Table;

WHILE (@id <= @max)
BEGIN
    SELECT @user_id = user_id FROM @Table WHERE Id = @id
    SELECT @first = first_trans FROM #First WHERE user_id = @user_id
    SELECT @first_trans_plus_72 = first_trans_plus_72 FROM #First WHERE user_id = @user_id
    SET @SQL = 'select * from Transactions 
                where transaction_ts between ' + @first + ' and ' + @first_trans_plus_72 + ' 
                and user_id = ' + @user_id + ';'
    PRINT(@SQL)
    EXEC(@SQL)
    SET @id = @id +1
END

This produces the right logical sql but the datetime variables are strings so the query errors out. I tried setting the datetime variables (@first and @first_trans_plus_72 as datetime but this resulted in a conversion error.

Is there a simpler way to do this?

Upvotes: 1

Views: 241

Answers (1)

Gordon Linoff
Gordon Linoff

Reputation: 1270391

Why would you use a loop for this when you can use a simple query?

select t.*
from (select t.*, min(transaction_ts) over (partition by user_id) as min_tts
      from transactions t
     ) t
where t.transaction_ts <= dateadd(hour, 72, min_tts);

In general, it is better to write code using set-based operations. It is simpler and performs much, much better.

You can incorporate this into an update, but I don't think that is necessary. The above selects the transactions. You can use group by user_id to summarize them -- say to count them or to sum the values.

Upvotes: 5

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