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MySQL foreign key constraints, cascade delete
...#2 (blue):
DELETE FROM categories WHERE (id = 2);
the DBMS will look at all the tables which have a foreign key pointing at the 'categories' table, and delete the records where the matching id is 2. Since we only defined the foreign key relationship in products_categories, you end up with this ta...
What is the best way to test for an empty string in Go?
... one that makes the code clear.
If I'm about to look at element x I typically write
len(s) > x, even for x == 0, but if I care about
"is it this specific string" I tend to write s == "".
It's reasonable to assume that a mature compiler will compile
len(s) == 0 and s == "" into the ...
What is “with (nolock)” in SQL Server?
...ly write new rows, you never update them.
– Jonathan Allen
Mar 26 '09 at 17:56
49
@Grauenwolf- An...
When to use Preorder, Postorder, and Inorder Binary Search Tree Traversal strategies
...efore inspecting any leaves, you pick pre-order because you will encounter all the roots before all of the leaves.
If you know you need to explore all the leaves before any nodes, you select post-order because you don't waste any time inspecting roots in search for leaves.
If you know that the tre...
What is the difference between gsub and sub methods for Ruby Strings
...ticed before. I've been using :gsub and it appears that they are essentially the same. Can anyone explain the difference to me? Thanks!
...
Extract a regular expression match
...
Use the new stringr package which wraps all the existing regular expression operates in a consistent syntax and adds a few that are missing:
library(stringr)
str_locate("aaa12xxx", "[0-9]+")
# start end
# [1,] 4 5
str_extract("aaa12xxx", "[0-9]+")
# [1]...
Profiling Django
...at queries are executed on each page and how much time they take. It's a really useful, powerful and easy to use tool.
Also, read recommendations about Django performance in Database access optimization from the documentation.
And Django performance tips by
Jacob Kaplan-Moss.
...
How to identify CAAnimation within the animationDidStop delegate?
... where I had a series of overlapping CATransition / CAAnimation sequences, all of which I needed to perform custom operations when the animations stopped, but I only wanted one delegate handler for animationDidStop.
...
What's the difference between --general-numeric-sort and --numeric-sort options in gnu sort
...
General numeric sort compares the numbers as floats, this allows scientific notation eg 1.234E10 but is slower and subject to rounding error (1.2345678 could come after 1.2345679), numeric sort is just a regular alphabetic sort that knows 10 comes after 9.
See http://www.gnu.o...
GDB corrupted stack frame - How to debug?
...
Those bogus adresses (0x00000002 and the like) are actually PC values, not SP values. Now, when you get this kind of SEGV, with a bogus (very small) PC address, 99% of the time it's due to calling through a bogus function pointer. Note that virtual calls in C++ are implemented ...