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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
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MySQL COUNT DISTINCT
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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
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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 ...
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...
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.
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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...
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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Using MySQL with Entity Framework [closed]
...link - users can now click right through rather than have to copy/paste or select/goto
– kͩeͣmͮpͥ ͩ
Apr 18 '11 at 13:58
7
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SQL SELECT WHERE field contains words
I need a select which would return results like this:
15 Answers
15
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MySQL ON DUPLICATE KEY - last insert id?
...LAST_INSERT_ID(3000)) ON DUPLICATE KEY UPDATE id = LAST_INSERT_ID(id + 1);
SELECT LAST_INSERT_ID();
If the prefix exists, it will increment it and populate last_insert_id.
If the prefix does not exist, it will insert the prefix with the value 3000 and populate last_insert_id with 3000.
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