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How do I add a foreign key to an existing SQLite table?
...child ADD CONSTRAINT fk_child_parent
FOREIGN KEY (parent_id)
REFERENCES parent(id);
SQLite doesn't support the ADD CONSTRAINT variant of the ALTER TABLE command (sqlite.org: SQL Features That SQLite Does Not Implement).
Therefore, the only way to add a foreig...
Why always ./configure; make; make install; as 3 separate steps?
... to add that it all makes sense, and still there could be a single command call that does all 3 steps with their default configuration. They all have a default configuration otherwise you couldn't simply call them without arguments.
– erikbwork
Feb 27 '13 at 12...
find vs find_by vs where
...its your needs best.
The find method is usually used to retrieve a row by ID:
Model.find(1)
It's worth noting that find will throw an exception if the item is not found by the attribute that you supply. Use where (as described below, which will return an empty array if the attribute is not foun...
Define variable to use with IN operator (T-SQL)
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DECLARE @mylist TABLE (Id int)
INSERT INTO @mylist
SELECT id FROM (VALUES (1),(2),(3),(4),(5)) AS tbl(id)
SELECT * FROM Mytable WHERE theColumn IN (select id from @mylist)
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A migration to add unique constraint to a combination of columns
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The problem with the model level validation is that it doesn't scale. Two servers could run the same data through at the same time (like a double tap on an api heavy app) I have two identical records in my DB right now and the model has the validation..
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SQL WHERE condition is not equal to?
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You can do like this
DELETE FROM table WHERE id NOT IN ( 2 )
OR
DELETE FROM table WHERE id <> 2
As @Frank Schmitt noted, you might want to be careful about the NULL values too. If you want to delete everything which is not 2(including the NULLs) then add O...
Aligning textviews on the left and right edges in Android layout
I am getting started with Android. I am having trouble getting a simple layout going.
9 Answers
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How to add a primary key to a MySQL table?
...mn, you can always add the primary key:
ALTER TABLE goods ADD PRIMARY KEY(id)
As to why your script wasn't working, you need to specify PRIMARY KEY, not just the word PRIMARY:
alter table goods add column `id` int(10) unsigned primary KEY AUTO_INCREMENT;
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Difference: std::runtime_error vs std::exception()
..._error subtree, letting all others to pass through (and fly further up the call stack).
P.S. Designing a useful exception class hierarchy (that would let you catch only the exception types you are interested in at each point of your code) is a non-trivial task. What you see in standard C++ library ...