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What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN? [duplicate]
...These pictures don't do it for me. Why is the top right picture not simply SELECT * FROM TableA;? Why is the top left picture not simply SELECT * FROM TableB;? Why is the top middle picture not SELECT * FROM A INTERSECT SELECT * FROM B ? etc
– onedaywhen
Sep 9 ...
Can a class member function template be virtual?
...ember functions are resolved statically. That is, the
member function is selected statically (at compile-time) based on the
type of the pointer (or reference) to the object.
In contrast, virtual member functions are resolved dynamically (at
run-time). That is, the member function is selec...
How to use Checkbox inside Select Option
The client has given me a design which has a Select Option menu containing a checkbox together with the item name as individual items in the list.
Is there anyway possible to add a checkbox inside a Select Option menu?
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What is the error “Every derived table must have its own alias” in MySQL?
...er), which can the be used to refer to it in the rest of the outer query.
SELECT ID FROM (
SELECT ID, msisdn FROM (
SELECT * FROM TT2
) AS T
) AS T
In your case, of course, the entire query could be replaced with:
SELECT ID FROM TT2
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What do 'real', 'user' and 'sys' mean in the output of time(1)?
...
(Ran out of chars in the prev comment so): More detail? Use perf [1], [2]. [1] perf.wiki.kernel.org/index.php/Main_Page [2] brendangregg.com/perf.html
– kaiwan
May 9 '15 at 7:46
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How can I capitalize the first letter of each word in a string?
... If the optional second argument sep is absent or None, runs of whitespace characters are replaced by a single space and leading and trailing whitespace are removed, otherwise sep is used to split and join the words.
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How to order by with union in SQL?
Is it possible to order when the data is come from many select and union it together? Such as
8 Answers
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Postgres: INSERT if does not exist already
...onditional INSERT in PostgreSQL:
INSERT INTO example_table
(id, name)
SELECT 1, 'John'
WHERE
NOT EXISTS (
SELECT id FROM example_table WHERE id = 1
);
CAVEAT This approach is not 100% reliable for concurrent write operations, though. There is a very tiny race condition between...
PostgreSQL function for last inserted ID
...e:
INSERT INTO persons (lastname,firstname) VALUES ('Smith', 'John');
SELECT currval('persons_id_seq');
The name of the sequence must be known, it's really arbitrary; in this example we assume that the table persons has an id column created with the SERIAL pseudo-type. To avoid relying on thi...
How to make the 'cut' command treat same sequental delimiters as one?
... page:
-s, --squeeze-repeats replace each input sequence of a repeated character
that is listed in SET1 with a single occurrence
of that character
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