大约有 40,000 项符合查询结果（耗时：0.0450秒） [XML]
Is R's apply family more than syntactic sugar?
... This is a little off topic, but for this specific example, data.table is even faster and I think "easier". library(data.table) dt<-data.table(X,Y,Z,key=c("Y,Z")) system.time(dt[,list(X_mean=mean(X)),by=c("Y,Z")])
– dnlbrky
Feb 22 '13 at 4:01
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PDO mysql: How to know if insert was successful
...some action and re-throwing the exception for the any other error (no such table for example) which will be reported to a programmer.
While again - just to tell a user something like "Your insert was successful" no condition is ever needed.
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Get second child using jQuery
...As in $(t).find('td').eq(1) to get the second <td>, if t was, say, a table and I needed to look down more than 1 node?
– Justin L.
Sep 8 '16 at 1:05
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How can I run a PHP script in the background after a form is submitted?
...s enough to cause it takes upwards of a minute to cycle through the entire table of subscribers and send out 150+ emails. (The emails are being sent individually as requested by the system administrators of our email server because of mass email policies.)
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SQL how to make null values come last when sorting ascending
I have a SQL table with a datetime field. The field in question can be null. I have a query and I want the results sorted ascendingly by the datetime field, however I want rows where the datetime field is null at the end of the list, not at the beginning.
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Unique constraint that allows empty values in MySQL
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@MianAnjum bolded: CREATE TABLE table (key int(11) NOT NULL AUTO_INCREMENT, field tinyint(1) DEFAULT NULL)
– Paul Nowak
Sep 19 '17 at 19:45
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Why do I get “Procedure expects parameter '@statement' of type 'ntext/nchar/nvarchar'.” when I try t
...be NVARCHAR
DECLARE @SQL VARCHAR(100)
SET @SQL = 'SELECT TOP 1 * FROM sys.tables'
EXECUTE sp_executesql @SQL
So:
DECLARE @SQL NVARCHAR(100)
SET @SQL = 'SELECT TOP 1 * FROM sys.tables'
EXECUTE sp_executesql @SQL
share
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How to find out what character key is pressed?
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Try:
<table>
<tr><td>Key:</td><td id="key"></td></tr>
<tr><td>Key Code:</td><td id="keyCode"></td></tr>
<tr><td>Event Code:</td><td ...
How to disable margin-collapsing?
...collapsing") entail using a 1px border or 1px padding. I find this unacceptable: the extraneous pixel complicates calculations for no good reason. Is there a more reasonable way to disable this margin-collapsing?
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How to get image height and width using java?
... byte: H is first four bits and V is second four bits
o Quantization table number-- one byte
The H and V sampling factors dictate the final size of the component they are associated with. For instance, the color space defaults to YCbCr and the H and V sampling factors for each component, Y, C...