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Unique constraint that allows empty values in MySQL
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Yes, you can do this. See the MySQL reference (version 5.5).
A UNIQUE index creates a constraint such that all values in the index must be distinct. An error occurs if you try to add a new row with a key value that matches an existing row. For all eng...
How to insert a line break in a SQL Server VARCHAR/NVARCHAR string
...NVARCHAR(100)
SET @text = 'This is line 1.' + CHAR(13) + 'This is line 2.'
SELECT @text
This prints out the following:
This is line 1.
This is line 2.
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When should I use Kruskal as opposed to Prim (and vice versa)?
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If you implement both Kruskal and Prim, in their optimal form : with a union find and a finbonacci heap respectively, then you will note how Kruskal is easy to implement compared to Prim.
Prim is harder with a fibonacci heap mainly because you have to maintain a book-keeping table to record the...
What do column flags mean in MySQL Workbench?
In MySQL Workbench table editor there are 7 column flags available: PK, NN, UQ, BIN, UN, ZF, AI.
3 Answers
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Using SSH keys inside docker container
... different base, and each of them begins a new stage of the build. You can selectively copy artifacts from one stage to another, leaving behind everything you don’t want in the final image.
Keeping this in mind here is my example of Dockerfile including three build stages. It's meant to create a...
Not equal != operator on NULL
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As a manual workaround, you could commonly SELECT * FROM MyTable WHERE coalesce(MyColumn, 'x') <> 'x' to assign a constant if it is NULL value, providing you give an appropriate datatype for the sentinel value x (in this case a string/char). This is TSQL syntax ...
Correct way to add external jars (lib/*.jar) to an IntelliJ IDEA project
...ps for adding external jars in IntelliJ IDEA:
Click File from the toolbar
Select Project Structure option (CTRL + SHIFT + ALT + S on Windows/Linux, ⌘ + ; on Mac OS X)
Select Modules at the left panel
Select Dependencies tab
Select + icon
Select 1 JARs or directories option
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海量数据相似度计算之simhash和海明距离 - 大数据 & AI - 清泛网 - 专注C/C++及内核技术
...对于结果的分析。分析前我们需要对这些数据去除重复，如何选择和设 通过 采集系统 我们采集了大量文本数据，但是文本中有很多重复数据影响我们对于结果的分析。分析前我们需要对这些数据去除重复，如何选择和设计文...
More elegant “ps aux | grep -v grep”
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@kxsong: | grep '[t]erminal' selects any line containing the word 'terminal' without putting the word 'terminal' into the process list. What are you trying to achieve with | grep '[r]oot' and how is it not working? There is likely to be a better solution...
MySQL Error 1215: Cannot add foreign key constraint
...the 4th point was my problem. It's kind of nasty - but I'm very very happy mysql did crash for that
– Sebas
Jun 16 '16 at 15:21
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