大约有 37,000 项符合查询结果（耗时：0.0416秒） [XML]
PostgreSQL - fetch the row which has the Max value for a column
...uted between 0 and 10k, trans_id uniformly distributed between 0 and 30),
By query cost, below, I am referring to Postgres' cost based optimizer's cost estimate (with Postgres' default xxx_cost values), which is a weighed function estimate of required I/O and CPU resources; you can obtain this by f...
MySQL Query GROUP BY day / month / year
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GROUP BY YEAR(record_date), MONTH(record_date)
Check out the date and time functions in MySQL.
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Windows git “warning: LF will be replaced by CRLF”, is that warning tail backward?
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warning: LF will be replaced by CRLF.
Depending on the editor you are using, a text file with LF wouldn't necessary be saved with CRLF: recent editors can preserve eol style. But that git config setting insists on changing those...
Simply make sure t...
Should I pass a shared_ptr by reference? [duplicate]
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In controlled circumstances you can pass the shared pointer by constant reference. Be sure that nobody is concurrently deleting the object, though this shouldn't be too hard if you're careful about to whom you give references.
In general, you should pass the shared pointer as a strai...
How does MySQL process ORDER BY and LIMIT in a query?
...0. A database will also process anything in the WHERE clause before ORDER BY.
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Group by month and year in MySQL
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GROUP BY YEAR(t.summaryDateTime), MONTH(t.summaryDateTime) DESC;
is what you want.
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Should we pass a shared_ptr by reference or by value?
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This question has been discussed and answered by Scott, Andrei and Herb during Ask Us Anything session at C++ and Beyond 2011. Watch from 4:34 on shared_ptr performance and correctness.
Shortly, there is no reason to pass by value, unless the goal is to share ownership ...
Multiple working directories with Git?
I'm not sure if this is something supported by Git, but in theory it seems like it should work to me.
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Include headers when using SELECT INTO OUTFILE?
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But it will not work if there is an ORDER BY in the SELECT clause. The header line can be anywhere in the generated file depending on the order.
– COil
May 19 '14 at 14:29
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must appear in the GROUP BY clause or be used in an aggregate function
... problem. Before SQL3 (1999), the selected fields must appear in the GROUP BY clause[*].
To workaround this issue, you must calculate the aggregate in a sub-query and then join it with itself to get the additional columns you'd need to show:
SELECT m.cname, m.wmname, t.mx
FROM (
SELECT cname,...