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Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths - why?
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I had a table that had a circular relationship with others and i was getting the same error. Turns out it is about the foreign key which was not nullable. If key is not nullable related object must be deleted and circular relations d...
What does “hashable” mean in Python?
... data structures use the hash value internally.
All of Python’s immutable built-in objects are hashable, while no mutable containers (such as lists or dictionaries) are. Objects which are instances of user-defined classes are hashable by default; they all compare unequal, and their hash value...
How do I create a foreign key in SQL Server?
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create table question_bank
(
question_id uniqueidentifier primary key,
question_exam_id uniqueidentifier not null,
question_text varchar(1024) not null,
question_point_value decimal,
constraint fk_questionbank_ex...
Remove characters except digits from string using Python?
...digs)
'1233344554552'
>>>
string.maketrans makes a translation table (a string of length 256) which in this case is the same as ''.join(chr(x) for x in range(256)) (just faster to make;-). .translate applies the translation table (which here is irrelevant since all essentially means iden...
Ship an application with a database
...re database from there. This is much quicker if the database has a lot of tables and other components. Upgrades are triggered by changing the database version number in the res/values/strings.xml file. Upgrades would then be accomplished by creating a new database externally, replacing the old dat...
Run a single migration file
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Note that if you do this, it probably won't update the schema_migrations table, but it seems like that's what you want anyway.
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How can I select rows with most recent timestamp for each key value?
I have a table of sensor data. Each row has a sensor id, a timestamp, and other fields. I want to select a single row with latest timestamp for each sensor, including some of the other fields.
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Discuz! X3 论坛标题字数突破80的限制 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...你的表的前缀，还有修改前一定要备份！！！）
ALTER TABLE `pre_forum_post` CHANGE `subject` `subject` varchar(255) NOT NULL;
ALTER TABLE `pre_forum_rsscache` CHANGE `subject` `subject` varchar(255) NOT NULL;
ALTER TABLE `pre_forum_thread` CHANGE `subject` `subject` varchar(255...
SQL Switch/Case in 'where' clause
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I'd say this is an indicator of a flawed table structure. Perhaps the different location types should be separated in different tables, enabling you to do much richer querying and also avoid having superfluous columns around.
If you're unable to change the structur...
How to list all properties of a PowerShell object
...Shell provides a set of formatting instructions that can affect either the table or list formats. These are usually meant to limit the display of reams of properties down to just the essential properties. However there are times when you really want to see everything. In those cases Format-List * wi...