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In Postgresql, force unique on combination of two columns
...ique (col1, col2)
)
autoincrement is not postgresql. You want a serial.
If col1 and col2 make a unique and can't be null then they make a good primary key:
CREATE TABLE someTable (
col1 int NOT NULL,
col2 int NOT NULL,
primary key (col1, col2)
)
...
Convert a matrix to a 1 dimensional array
...do as.vector() on the matrix. You might want to transpose the matrix first if you want it by rows or columns.
> m=matrix(1:12,3,4)
> m
[,1] [,2] [,3] [,4]
[1,] 1 4 7 10
[2,] 2 5 8 11
[3,] 3 6 9 12
> as.vector(m)
[1] 1 2 3 4 5 6 7 8 9 10 11 1...
How to extract a string using JavaScript Regex?
... I would combine this with @barkmadley 's || [null, null] since if the match fails, arr would be null and arr[1] would throw an exception
– Kunal
May 5 '16 at 16:44
...
How to sort a list of strings numerically?
...3","22","23","4","2","200"]
list1 = [int(x) for x in list1]
list1.sort()
If for some reason you need to keep strings instead of ints (usually a bad idea, but maybe you need to preserve leading zeros or something), you can use a key function. sort takes a named parameter, key, which is a function t...
编程基础与事件状态 01：让按钮响应你的任务 · App Inventor 2 中文网
...有工程时，同名事件合并处理。
when 按钮_开始.Click() {
if trim(文本输入框_任务.Text) = "" { 标签_状态.Text = "请填写任务" }
else { 标签_状态.Text = join("开始：", trim(文本输入框_任务.Text)) }
}
中途检查与排错
本课以...
App Inventor 2 ECharts 拓展：基于 ECharts 强大的个性化数据图表展示 · ...
...度记录, random(20, 35))
listAdd(时刻表, length(时刻表) + 1)
if length(温度记录) > 20 {
listRemove(温度记录, 1)
listRemove(时刻表, 1)
}
ECharts1.Line("实时温度", ["温度"], 时刻表, [温度记录], true)
}
响应点击，做联动
...
Commit changes to a different branch than the currently checked out branch with subversion
...;
Optional: Tick [*] Switch working copy to new branch/tag. This is useful if you are planning to keep working on the new branch. Although you can switch to it later too.
Try to find the OK button. Hint: it is in the lower part of the window centred.
Enjoy!
...
C# nullable string error
...r null after getting it from the query string. Or use String.IsNullOrEmpty if you want to handle empty string values the same as null.
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How to determine the number of days in a month in SQL Server?
...
You can use the following with the first day of the specified month:
datediff(day, @date, dateadd(month, 1, @date))
To make it work for every date:
datediff(day, dateadd(day, 1-day(@date), @date),
dateadd(month, 1, dateadd(day, 1-day(@date), @date)))
...
How to add a ScrollBar to a Stackpanel
...an interface contract (IScrollInfo). Setting this property has no effect. If you require physical scrolling instead of logical scrolling, wrap the StackPanel in a ScrollViewer and set its CanContentScroll property to false."
– Skinner
Jul 25 '17 at 1:55
...