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Select multiple columns in data.table by their numeric indices
How can we select multiple columns using a vector of their numeric indices (position) in data.table ?
5 Answers
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Get index of selected option with jQuery
I'm a little bit confused about how to get an index of a selected option from a HTML <select> item.
7 Answers
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Retrieving the last record in each group - MySQL
...x, we can write greatest-n-per-group queries:
WITH ranked_messages AS (
SELECT m.*, ROW_NUMBER() OVER (PARTITION BY name ORDER BY id DESC) AS rn
FROM messages AS m
)
SELECT * FROM ranked_messages WHERE rn = 1;
Below is the original answer I wrote for this question in 2009:
I write the solu...
How does delete[] know it's an array?
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try size_t size = *(reinterpret_cast<size_t *>(pArray) - 1) instead
– user6377043
Aug 12 '17 at 11:42
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Why is isNaN(null) == false in JS?
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But then at least a string is cast into a NaN object, as isNaN("text") returns true.
– Hanno Fietz
Sep 22 '08 at 15:45
add a comme...
what is the difference between GROUP BY and ORDER BY in sql
... SUM, COUNT, AVG, etc).
TABLE:
ID NAME
1 Peter
2 John
3 Greg
4 Peter
SELECT *
FROM TABLE
ORDER BY NAME
=
3 Greg
2 John
1 Peter
4 Peter
SELECT Count(ID), NAME
FROM TABLE
GROUP BY NAME
=
1 Greg
1 John
2 Peter
SELECT NAME
FROM TABLE
GROUP BY NAME
HAVING Count(ID) > 1
=
Peter
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How to determine the number of days in a month in SQL Server?
...er of days in the month.
DECLARE @ADate DATETIME
SET @ADate = GETDATE()
SELECT DAY(EOMONTH(@ADate)) AS DaysInMonth
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C pointers : pointing to an array of fixed size
...ill, nothing prevents you or an incompetent or malevolent coder from using casts to fool the compiler into treating your struct as one of a different size. The almost unshackled ability to do this kind of thing is a part of C's design.
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Implement paging (skip / take) functionality with this query
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In SQL Server 2012 it is very very easy
SELECT col1, col2, ...
FROM ...
WHERE ...
ORDER BY -- this is a MUST there must be ORDER BY statement
-- the paging comes here
OFFSET 10 ROWS -- skip 10 rows
FETCH NEXT 10 ROWS ONLY; -- take 10 rows
If we want...
'IF' in 'SELECT' statement - choose output value based on column values
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SELECT id,
IF(type = 'P', amount, amount * -1) as amount
FROM report
See http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html.
Additionally, you could handle when the condition is null. In the case of...