How to Select First N Rows from a Table in T-Sql

how to select first N rows from a table in T-SQL?

select top(@count) * from users

If @count is a constant, you can drop the parentheses:

select top 42 * from users

(the latter works on SQL Server 2000 too, while the former requires at least 2005)

Selecting the first N rows of each group ordered by date

As well as the row_number solution, another option is CROSS APPLY(SELECT TOP:

SELECT m.masterid,
       d.detailid,
       m.numbers,
       d.date_time,
       d.value
    FROM masters AS m
    CROSS APPLY (
        SELECT TOP (3) *
        FROM details AS d
        WHERE d.date_time >= '2020-01-01'
        AND m.masterid = d.masterid
    ) AS d
    WHERE m.tags LIKE '%Tag2%'
    ORDER BY m.masterid DESC,
             d.date_time;

This may be faster or slower than row_number, mostly depending on cardinalities (quantity of rows) and indexing.

If indexing is good and it's a small number of rows it will usually be faster. If the inner table needs sorting or you are anyway selecting most rows then use row_number.

SQL - Select first 10 rows only?

In SQL server, use:

select top 10 ...

e.g.

select top 100 * from myTable
select top 100 colA, colB from myTable

In MySQL, use:

select ... order by num desc limit 10

How to get N rows starting from row M from sorted table in T-SQL

UPDATE If you you are using SQL 2012 new syntax was added to make this really easy. See Implement paging (skip / take) functionality with this query

I guess the most elegant is to use the ROW_NUMBER function (available from MS SQL Server 2005):

WITH NumberedMyTable AS
(
    SELECT
        Id,
        Value,
        ROW_NUMBER() OVER (ORDER BY Id) AS RowNumber
    FROM
        MyTable
)
SELECT
    Id,
    Value
FROM
    NumberedMyTable
WHERE
    RowNumber BETWEEN @From AND @To

How to select the first N rows of each group?

You can do the counting using a correlated subquery:

SELECT b.BookId, a.AuthorId, a.AuthorName, b.Title
FROM Author a join
     Book b
     on a.AuthorId = b.AuthorId
where (select count(*)
       from book b2
       where b2.bookId <= b.BookId and b2.AuthorId = b.AuthorId
      ) <= 2;

For a small database this should be fine. If you create a composite index on Book(AuthorId, BookId) then that will help the query.

How to skip the first n rows in sql query

Query: in sql-server

DECLARE @N INT = 5 --Any random number

SELECT * FROM (
        SELECT ROW_NUMBER() OVER(ORDER BY ID) AS RoNum
              , ID --Add any fields needed here (or replace ID by *)
        FROM TABLE_NAME
) AS tbl 
WHERE @N < RoNum
ORDER BY tbl.ID

This will give rows of Table, where rownumber is starting from @N + 1.

Select first N rows of all non-empty SQL Server tables

SQL Server has the unsupported sp_MSforeachtable. So, you can do:

exec sp_MSforeachtable @command1='select top (3) * from ? where exists (select 1 from ?)';

Otherwise, you would be using a cursor or other looping mechanism to achieve basically the same thing.

EDIT:

Jeroen makes a very good suggestion:

exec sp_MSforeachtable @command1='if exists (select 1 from ?) select top (3) ''?'' as table_name, t.* from ? t';

This also adds the table name for extra spice.

SQL Server SELECT LAST N Rows

You can do it by using the ROW NUMBER BY PARTITION Feature also. A great example can be found here:

I am using the Orders table of the Northwind database... Now let us retrieve the Last 5 orders placed by Employee 5:

SELECT ORDERID, CUSTOMERID, OrderDate
FROM
(
    SELECT ROW_NUMBER() OVER (PARTITION BY EmployeeID ORDER BY OrderDate DESC) AS OrderedDate,*
    FROM Orders
) as ordlist

WHERE ordlist.EmployeeID = 5
AND ordlist.OrderedDate <= 5

Get top 1 row of each group

;WITH cte AS
(
   SELECT *,
         ROW_NUMBER() OVER (PARTITION BY DocumentID ORDER BY DateCreated DESC) AS rn
   FROM DocumentStatusLogs
)
SELECT *
FROM cte
WHERE rn = 1

If you expect 2 entries per day, then this will arbitrarily pick one. To get both entries for a day, use DENSE_RANK instead

As for normalised or not, it depends if you want to:

• maintain status in 2 places
• preserve status history
• ...

As it stands, you preserve status history. If you want latest status in the parent table too (which is denormalisation) you'd need a trigger to maintain "status" in the parent. or drop this status history table.

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