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Use email address as primary key?
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@onedaywhen: Yep! Otherwise why would SQL support cascading updates?
– Bill Karwin
Sep 27 '10 at 17:52
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How to sort objects by multiple keys in Python?
...der.
This means that the equivalent of ORDER BY name ASC, age DESC (using SQL notation) for a list of dictionaries can be done like this:
items.sort(key=operator.itemgetter('age'), reverse=True)
items.sort(key=operator.itemgetter('name'))
Note how the items are first sorted by the "lesser" attri...
How to implement a many-to-many relationship in PostgreSQL?
...itle is self-explanatory. How do you create the table structure in PostgreSQL to make a many-to-many relationship.
1 Answe...
What's the best way to join on the same table twice?
...o corresponding exists on the right. For me this works in Microsoft Access SQL (they require the parenthesis!)
SELECT t.PhoneNumber1, t.PhoneNumber2, t.PhoneNumber3
t1.SomeOtherFieldForPhone1, t2.someOtherFieldForPhone2, t3.someOtherFieldForPhone3
FROM
(
(
Table1 AS t LEFT JOIN Table2 AS t3 ...
“open/close” SqlConnection or keep open?
...ple static classes with static methods. Each of these methods opens/closes SQL connection when called:
6 Answers
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Give all the permissions to a user on a DB
...a DATABASE vs SCHEMA?
Grant privileges for a particular database in PostgreSQL
How to grant all privileges on views to arbitrary user
Consider upgrading to a current version.
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MySQL JOIN the most recent row only?
...virtually instantaneous (WorkBench literally says 0.000 seconds, even with sql_no_cache set), whereas doing the search in the join took multiple seconds to complete. Still baffled, but I mean you can't argue with results like that.
– Brian Leishman
Mar 21 '17 a...
ActiveRecord: size vs count
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As the other answers state:
count will perform an SQL COUNT query
length will calculate the length of the resulting array
size will try to pick the most appropriate of the two to avoid excessive queries
But there is one more thing. We noticed a case where size acts differe...
How to display unique records from a has_many through relationship?
...ou use the :uniq option on your association (as shown in my answer) or the SQL DISTINCT stmt (e.g. has_many :products, :through => :orders, :select => "DISTINCT products.*). In the first case, ALL records are fetched and rails removes the duplicates for you. In the later case, only non-duplica...
How do MySQL indexes work?
I am really interested in how MySQL indexes work, more specifically, how can they return the data requested without scanning the entire table?
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