大约有 41,000 项符合查询结果（耗时：0.0318秒） [XML]
Join vs. sub-query
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@JinghuiNiu Customers who bought expensive items: select custid from cust join bought using (custid) where price > 500. If a customer bought multiple expensive items, you'll get double-ups. To fix this, select custid from cust where exists (select * from bought where cust...
Get first day of week in SQL Server
...in that there should be some sensible logic built in to round up or down:
SELECT DATEDIFF(YEAR, '2010-01-01', '2011-12-31');
SELECT DATEDIFF(YEAR, '2010-12-31', '2011-01-01');
To answer how to get a Sunday:
If you want a Sunday, then pick a base date that's not a Monday but rather a Sunday. For ...
How do I programmatically set the value of a select box element using JavaScript?
I have the following HTML <select> element:
17 Answers
17
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Counting DISTINCT over multiple columns
... function turns the ints into varchars to make the distinct more reliable
SELECT COUNT(DISTINCT (CHECKSUM(DocumentId,DocumentSessionId)) + CHECKSUM(REVERSE(DocumentId),REVERSE(DocumentSessionId)) )
FROM DocumentOutPutItems
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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 to select only the first rows for each unique value of a column
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A very simple answer if you say you don't care which address is used.
SELECT
CName, MIN(AddressLine)
FROM
MyTable
GROUP BY
CName
If you want the first according to, say, an "inserted" column then it's a different query
SELECT
M.CName, M.AddressLine,
FROM
(
SELECT
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SELECT * WHERE NOT EXISTS
...uming these tables should be joined on employeeID, use the following:
SELECT *
FROM employees e
WHERE NOT EXISTS
(
SELECT null
FROM eotm_dyn d
WHERE d.employeeID = e.id
)
You can join these tables with a LEFT JOIN keyword and filter out the...
How to select date from datetime column?
...ry.
Use BETWEEN or >, <, = operators which allow to use an index:
SELECT * FROM data
WHERE datetime BETWEEN '2009-10-20 00:00:00' AND '2009-10-20 23:59:59'
Update: the impact on using LIKE instead of operators in an indexed column is high. These are some test results on a table with 1,...
Difference between two dates in MySQL
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SELECT TIMEDIFF('2007-12-31 10:02:00','2007-12-30 12:01:01');
-- result: 22:00:59, the difference in HH:MM:SS format
SELECT TIMESTAMPDIFF(SECOND,'2007-12-30 12:01:01','2007-12-31 10:02:00');
-- result: 79259 the differenc...
Retrieve filename from file descriptor in C
... this snippet:
#include <sys/syslimits.h>
#include <fcntl.h>
char filePath[PATH_MAX];
if (fcntl(fd, F_GETPATH, filePath) != -1)
{
// do something with the file path
}
Since I never remember where MAXPATHLEN is defined, I thought PATH_MAX from syslimits would be fine.
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