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Swapping column values in MySQL
...test s1, swap_test s2 SET s1.x=s1.y, s1.y=s2.x WHERE s1.id=s2.id;
Essentially, the 1st table is the one getting updated and the 2nd one is used to pull the old data from.
Note that this approach requires a primary key to be present.
This is my test schema:
CREATE TABLE `swap_test` (
`id` int(1...
Pointers in C: when to use the ampersand and the asterisk?
... work differently when you're working with arrays, strings or when you're calling functions with a pointer copy of a variable. It's difficult to see a pattern of logic inside all of this.
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How can I suppress all output from a command using Bash?
...ant error messages to be sent there, use one of (the first may not work in all shells):
scriptname &>/dev/null
scriptname >/dev/null 2>&1
scriptname >/dev/null 2>/dev/null
And, if you want to record the messages, but not see them, replace /dev/null with an actual file, such...
JavaScript by reference vs. by value [duplicate]
...
My understanding is that this is actually very simple:
Javascript is always pass by value, but when a variable refers to an object (including arrays), the "value" is a reference to the object.
Changing the value of a variable never changes the underlying prim...
How to get process ID of background process?
...olling terminal. A script will not necessarily have a terminal attached at all so job control will not necessarily be available.
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What does “var FOO = FOO || {}” (assign a variable or an empty object to that variable) mean in Java
...tional arguments and initialize them to defaults if not provided: function foo(arg1, optarg1, optarg2) { optarg1 = optarg1 || 'default value 1'; optarg2 = optart2 || 'defalt value 2';}
– crazy2be
Jun 22 '11 at 19:24
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Is there a combination of “LIKE” and “IN” in SQL?
... volume this could be quite long.
– Pierre-Gilles Levallois
Aug 21 '12 at 13:49
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With SQL Serve...
How to create id with AUTO_INCREMENT on Oracle?
...NCREMENT by 1),
c2 VARCHAR2(10)
);
Alternatively, Oracle 12 also allows to use a sequence as a default value:
CREATE SEQUENCE dept_seq START WITH 1;
CREATE TABLE departments (
ID NUMBER(10) DEFAULT dept_seq.nextval NOT NULL,
DESCRIPTION VARCHAR2(50) NOT NULL);
ALTER T...
Join vs. sub-query
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@user1735921 IMO it depends ... Generally, it's very important the readability of the code, because it is of great importance for later management of it... Let's remember the famous statement of Donald Knuth: "Premature optimization is the root of all evil (or a...
What is the exact problem with multiple inheritance?
I can see people asking all the time whether multiple inheritance should be included into the next version of C# or Java. C++ folks, who are fortunate enough to have this ability, say that this is like giving someone a rope to eventually hang themselves.
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