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updating table rows in postgres using subquery
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Postgres allows:
UPDATE dummy
SET customer=subquery.customer,
address=subquery.address,
partn=subquery.partn
FROM (SELECT address_id, customer, address, partn
FROM /* big hairy SQL */ ...) AS subquery
WHERE dummy.addre...
Linq to Entities join vs groupjoin
...groups. This can be turned into a flat list of parent-child pairs by two small additions:
from p in parents
join c in children on p.Id equals c.Id into g // <= into
from c in g.DefaultIfEmpty() // <= flattens the groups
select new { Parent = p.Value, Child = c?.ChildValue }
The ...
How slow are .NET exceptions?
...e, where failure means "The file isn't in the format it's meant to be, I really don't want to try to handle this as I don't know what else might be wrong."
When using exceptions in "only reasonable circumstances" I've never seen an application whose performance was significantly impaired by excepti...
Display an array in a readable/hierarchical format
... to get the data as string. Now you can return '<pre>'.print_r(User::all(), true); from your routes file.
– DutGRIFF
Nov 5 '14 at 19:43
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iPhone Simulator location
Where on my machine is the iPhone simulator installed?
17 Answers
17
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Using unset vs. setting a variable to empty
...t; unset var
/home/user1> echo $var
-bash: var: unbound variable
So really, it depends on how you are going to test the variable.
I will add that my preferred way of testing if it is set is:
[[ -n $var ]] # True if the length of $var is non-zero
or
[[ -z $var ]] # True if zero length
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How can you diff two pipelines in Bash?
...dev/fd/63 to get a filename that the command can open and read from to actually read from an already-open file descriptor that bash set up before exec'ing the command. (i.e. bash uses pipe(2) before fork, and then dup2 to redirect from the output of quux to an input file descriptor for diff, on fd ...
How to save traceback / sys.exc_info() values in a variable?
...traceback.format_exc()
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>>> print var
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
ValueError: invalid literal for int() with base 10: 'k'
You should however take a look at the traceback documentation, as you might find there more suitable metho...
Inherit from a generic base class, apply a constraint, and implement an interface in C#
..., a class only gets one where clause, and it goes at the end for any & all generic type constraints.
– Andy V
Aug 22 '16 at 16:18
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Memory address of variables in Java
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Actually, the identity hash code cannot change, otherwise the contract of hashCode() would be violated.
– Matt McHenry
Jun 28 '13 at 18:36
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