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difference between primary key and unique key
...rimary Key is a unique key identifier of the record
Unique Key:
Can be more than one unique key in one table
Unique key can have NULL values
It can be a candidate key
Unique key can be NULL ; multiple rows can have NULL values and therefore may not be considered "unique"
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What are the differences between Chosen and Select2?
Chosen and Select2 are the two more popular libraries for extending selectboxes.
11 Answers
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Python Empty Generator Function
...just replaces a no-op if statement with a no-op yield statement. But it is more idiomatic. Note that just using yield doesn't work.
>>> def f():
... yield
...
>>> list(f())
[None]
Why not just use iter(())?
This question asks specifically about an empty generator function....
Difference between CTE and SubQuery?
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Sorry, I should have been more clearer in the my question. What would be the difference between CTE and Subquery in the context where CTE is used LIKE subquery?
– dance2die
Apr 1 '09 at 19:22
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When and why should I use fragments in Android applications? [duplicate]
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Fragments are more of a UI benefit in my opinion. It's convenient for the user sometimes to see two different views of two different classes on the same screen. If, in your moment of creativity, you decide it would be nice to display you...
Manually raising (throwing) an exception in Python
...d raising a generic Exception. To catch it, you'll have to catch all other more specific exceptions that subclass it.
Problem 1: Hiding bugs
raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.
For example:
def demo_bad_catch():
try:
raise ValueError('Repres...
Concatenate text files with Windows command line, dropping leading lines
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more +2 file2.txt > temp
type temp file1.txt > out.txt
or you can use copy. See copy /? for more.
copy /b temp+file1.txt out.txt
share
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What do 'real', 'user' and 'sys' mean in the output of time(1)?
...ocess has multiple threads (and this process is running on a computer with more than one processor) it could potentially exceed the wall clock time reported by Real (which usually occurs). Note that in the output these figures include the User and Sys time of all child processes (and their descenda...
Difference between numpy.array shape (R, 1) and (R,)
...hape (R, 1) but some return (R,) . This will make matrix multiplication more tedious since explicit reshape is required. For example, given a matrix M , if we want to do numpy.dot(M[:,0], numpy.ones((1, R))) where R is the number of rows (of course, the same issue also occurs column-wise)....
What is sharding and why is it important?
...ership easily and automatically, and query only the relevant shard.
Some more information about sharding:
Firstly, each database server is identical, having the same table structure. Secondly, the data records are logically split up in a sharded database. Unlike the partitioned database, each ...