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App Inventor 2 UrsAI2UDP 拓展 - UDP广播通信协议 · App Inventor 2 中文网
... 发送和接收文本 (URSAI2UDPTest)
此示例展示了如何发送和接收文本。
示例中的块并不难理解。大多数块涉及输入项的验证。
发送和接收字节数组 (UDPBinaryTest)
此示例展示了如何发送和接收字节...
GetProperties() to return all properties for an interface inheritance hierarchy
...(new Type[] { type })
.Concat(type.GetInterfaces())
.SelectMany(i => i.GetProperties());
}
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MySQL load NULL values from CSV data
...can see empty strings '' when they download a csv (using IFNULL(Col,'') in SELECT INTO OUTFILE query) for excel but then uploads accept them as null vs having to deal with \N in the csv. Thanks!
– chrisan
Sep 29 '13 at 15:47
...
Explicit vs implicit SQL joins
...e joined and how they are joined. Try compare larger SQL queries where you selecting from 8 different tables and you have lots of filtering in the where. By using join syntax you separate out the parts where the tables are joined, to the part where you are filtering the rows.
...
MySQL COUNT DISTINCT
...
Select
Count(Distinct user_id) As countUsers
, Count(site_id) As countVisits
, site_id As site
From cp_visits
Where ts >= DATE_SUB(NOW(), INTERVAL 1 DAY)
Group By site_id
...
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
...
Clear MySQL query cache without restarting server
...not clear it for me. Also, MySQL server restart does not help. An explicit SELECT SQL_NO_CACHE does the trick, but not RESET QUERY CACHE. sync && echo 3 | sudo tee /proc/sys/vm/drop_caches from the other answer didn't help, too.
– Jānis Elmeris
Aug 24 ...
MySQL, update multiple tables with one query
...'blah';
To see what this is going to update, you can convert this into a select statement, e.g.:
SELECT t2.t1_id, t2.t3_id, t1.a, t2.b, t2.c AS t2_c, t3.c AS t3_c
FROM t1
INNER JOIN t2 ON t2.t1_id = t1.id
INNER JOIN t3 ON t2.t3_id = t3.id
WHERE t1.a = 'blah';
An example using the same tables as...
What does mysql error 1025 (HY000): Error on rename of './foo' (errorno: 150) mean?
... have to find the name used to index it. To find that, issue the following select:
SHOW CREATE TABLE region;
This should show you the name of the index, something like this:
CONSTRAINT region_ibfk_1 FOREIGN
KEY (country_id) REFERENCES
country (id) ON DELETE NO
ACTION ON UPDATE NO ACT...
SQL SELECT WHERE field contains words
I need a select which would return results like this:
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