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Does MySQL ignore null values on unique constraints?
...ws multiple NULLs in a column with a unique constraint.
CREATE TABLE table1 (x INT NULL UNIQUE);
INSERT table1 VALUES (1);
INSERT table1 VALUES (1); -- Duplicate entry '1' for key 'x'
INSERT table1 VALUES (NULL);
INSERT table1 VALUES (NULL);
SELECT * FROM table1;
Result:
x
NULL
NULL
1
This i...
select and update database record with a single queryset
...et object update method:
MyModel.objects.filter(pk=some_value).update(field1='some value')
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Check if my app has a new version on AppStore
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91
Here is a simple code snippet that lets you know if the current version is different
-(BOOL) ne...
How do I return multiple values from a function? [closed]
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14 Answers
14
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Why is i++ not atomic?
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125
i++ is probably not atomic in Java because atomicity is a special requirement which is not pre...
Avoid duplicates in INSERT INTO SELECT query in SQL Server
...
Using NOT EXISTS:
INSERT INTO TABLE_2
(id, name)
SELECT t1.id,
t1.name
FROM TABLE_1 t1
WHERE NOT EXISTS(SELECT id
FROM TABLE_2 t2
WHERE t2.id = t1.id)
Using NOT IN:
INSERT INTO TABLE_2
(id, name)
SELECT t1.id,
t1.name
F...
Cluster analysis in R: determine the optimal number of clusters
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1024
If your question is how can I determine how many clusters are appropriate for a kmeans analys...
How to get a list of file names in different lines
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10 Answers
10
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Count number of files within a directory in Linux? [closed]
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1 Answer
1
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C++/COM VARIANT实现二维数组 - C/C++ - 清泛网 - 专注C/C++及内核技术
...率。下面以两种不同方式来实现VARIANT二维数组的操作。
1、使用SAFEARRAY实现二维数组
SAFEARRAY安全数组可以实现多维数组，SAFEARRAY实现的步骤可以大致分为三步。
（1）创建SAFEARRAY安全数组，包括设置数组元素的类型、数据的维...