大约有 40,000 项符合查询结果（耗时：0.0228秒） [XML]
Can you have if-then-else logic in SQL? [duplicate]
... in dbs it is not optimal because this syntax is procedural - it would be orders of magnitude slower than a proper set based query.
– mson
Feb 28 '13 at 13:42
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How do I find the MySQL my.cnf location
... it will load each of them & values override each other (in the listed order, I think). Also, the --defaults-file parameter can override the whole thing, so... basically, it's a huge pain in the butt.
But thanks to it being so confusing, there's a good chance it's just in /etc/my.cnf.
(if you...
Can you control how an SVG's stroke-width is drawn?
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You can use CSS to style the order of stroke and fills. That is, stroke first and then fill second, and get the desired effect.
MDN on paint-order: https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/paint-order
CSS code:
paint-order: stroke;
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must appear in the GROUP BY clause or be used in an aggregate function
...ax:
SELECT DISTINCT ON (cname)
cname, wmname, avg
FROM
makerar
ORDER BY
cname, avg DESC ;
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Efficient paging in SQLite with millions of records
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Please note that you always have to use an ORDER BY clause; otherwise, the order is arbitrary.
To do efficient paging, save the first/last displayed values of the ordered field(s), and continue just after them when displaying the next page:
SELECT *
FROM MyTable
WHE...
How to output MySQL query results in CSV format?
...ipes.com/rx/1475/save-mysql-query-results-into-a-text-or-csv-file/
SELECT order_id,product_name,qty
FROM orders
WHERE foo = 'bar'
INTO OUTFILE '/var/lib/mysql-files/orders.csv'
FIELDS TERMINATED BY ','
ENCLOSED BY '"'
LINES TERMINATED BY '\n';
Using this command columns names will not be exported...
What is the best way to use a HashMap in C++?
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The standard library includes the ordered and the unordered map (std::map and std::unordered_map) containers. In an ordered map the elements are sorted by the key, insert and access is in O(log n). Usually the standard library internally uses red black trees ...
Get last element of Stream/List in a one-liner
...reduce((first, second) -> second);
This implementations works for all ordered streams (including streams created from Lists). For unordered streams it is for obvious reasons unspecified which element will be returned.
The implementation works for both sequential and parallel streams. That migh...
The multi-part identifier could not be bound
...GROUP BY maxa
) AS dkcd ON dkcd.maxa = a.maxa
WHERE a.maxa <> '99'
ORDER BY a.maxa
Here the tables a and b are joined first, then the result is joined to dkcd. Basically, this is the same query as yours, only using a different syntax for one of the joins, which makes a great difference: th...
Is it possible to GROUP BY multiple columns using MySQL?
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Preference of left to right is applied to the ascending order of the groupings and not the column group preference. GROUP BY applies col1+col2. e.g. col1 = 1, 2, 1, 2 | col2 = 1, 2, 3, 2 and running GROUP BY col1,col2 would return 1,1|1,3|2,2 as opposed to 1,1|2,2 as suggested. Wh...