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Is there a good reason I see VARCHAR(255) used so often (as opposed to another length)?
...p being the effective maximum if you want to use UTF-8 and have the column indexed (because of index length limitations).
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String's Maximum length in Java - calling length() method
..., which is 2^31 - 1 (or approximately 2 billion.)
In terms of lengths and indexing of arrays, (such as char[], which is probably the way the internal data representation is implemented for Strings), Chapter 10: Arrays of The Java Language Specification, Java SE 7 Edition says the following:
The...
How to represent empty char in Java Character class
... main(String[] args) throws Exception {
String s = "abcdefg";
int index = s.indexOf('d');
// delete a char from a char[]
char[] array = s.toCharArray();
char[] tmp = new char[array.length-1];
System.arraycopy(array, 0, tmp, 0, index);
System.arraycopy(array, index+1, tm...
Algorithm to return all combinations of k elements from n
...hm 382: Combinations of M out of N Objects' (1970)
The algorithm in C...
Index of Combinations in Lexicographical Order (Buckles Algorithm 515)
You can also reference a combination by its index (in lexicographical order). Realizing that the index should be some amount of change from right to lef...
Pandas DataFrame Groupby two columns and get counts
...e your second question:
In [56]: df.groupby(['col5','col2']).size().reset_index().groupby('col2')[[0]].max()
Out[56]:
0
col2
A 3
B 2
C 1
D 3
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schema builder laravel migrations unique on two columns
...
The second param is to manually set the name of the unique index. Use an array as the first param to create a unique key across multiple columns.
$table->unique(array('mytext', 'user_id'));
or (a little neater)
$table->unique(['mytext', 'user_id']);
...
Git file permissions on Windows
...ing command adds user execute permission to an arbitrary file:
git update-index --chmod=+x <file>
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Meaning
...ed handlers, such as .html, .jpg, .doc, but also for classic ASP (.asp) or PHP (.php) extensions. See "How to Take Advantage of IIS Integrated Pipeline" for an example of enabling ASP.NET modules to run for all content.
You can also use a shortcut to enable all managed (ASP.NET) modules to run for a...
联网 App 第 4 课：图片上传，压缩后用 Web 客户端传到服务器、列表直接显...
...求内容。它与浏览器表单的 multipart/form-data 不同：依赖 PHP $_FILES 的普通上传接口或要求 multipart 的图床，不能直接替换本课 /upload 地址。仅手动设置 Content-Type 也不会生成表单分隔符、文件字段和附加字段。对象存储应以具体接...
Find size of an array in Perl
...dard way to get an array's size.
The second way actually returns the last index of the array, which is not (usually) the same as the array size.
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