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Legality of COW std::string implementation in C++11
...be seen in the following if COW were allowed: std::string a("something"); char& c1 = a[0]; std::string b(a); char& c2 = a[1]; c1 is a reference to a. You then "copy" a. Then, when you attempt to take the reference the second time, it has to make a copy to get a non-const reference since...
MySQL - UPDATE query based on SELECT Query
...can go here
ANSI SQL syntax:
UPDATE tableA SET validation_check =
(SELECT if(start_DTS > end_DTS, 'VALID', '') AS validation_check
FROM tableA
INNER JOIN tableB ON name_A = name_B
WHERE id_A = tableA.id_A)
Pick whichever one seems most natural to you.
...
How to get ID of the last updated row in MySQL?
...)
SET @update_id := 0;
UPDATE some_table SET column_name = 'value', id = (SELECT @update_id := id)
WHERE some_other_column = 'blah' LIMIT 1;
SELECT @update_id;
EDIT by aefxx
This technique can be further expanded to retrieve the ID of every row affected by an update statement:
SET @uids := nul...
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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Check if table exists in SQL Server
...nge from version to version.
To check if a table exists use:
IF (EXISTS (SELECT *
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'TheSchema'
AND TABLE_NAME = 'TheTable'))
BEGIN
--Do Stuff
END
...
SQL RANK() versus ROW_NUMBER()
...he first 3 rows are tied when ordered by ID)
WITH T(StyleID, ID)
AS (SELECT 1,1 UNION ALL
SELECT 1,1 UNION ALL
SELECT 1,1 UNION ALL
SELECT 1,2)
SELECT *,
RANK() OVER(PARTITION BY StyleID ORDER BY ID) AS 'RANK',
ROW_NUMBER() OVER(PARTITION BY Style...
Fastest check if row exists in PostgreSQL
...
Use the EXISTS key word for TRUE / FALSE return:
select exists(select 1 from contact where id=12)
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How to convert int to QString?
...t might very well work but internally, the operator+(const QString &s, char c) implementation is called, and the string wont contain the integer as number but its QChar::fromAscii(c) equivalent
– x29a
Jul 23 '15 at 8:19
...
How to declare a variable in MySQL?
...at has not been
initialized, it has a value of NULL and a type of string.
SELECT @var_any_var_name
You can initialize a variable using SET or SELECT statement:
SET @start = 1, @finish = 10;
or
SELECT @start := 1, @finish := 10;
SELECT * FROM places WHERE place BETWEEN @start AND @finish...
How to convert hex to rgb using Java?
...
For those who want a 3 character version as well, note that in the 3 character case each value must be * 255 / 16. I tested this with "000", "aaa", and "fff", and they all work properly now.
– Andrew
Apr 14 '...