大约有 3,610 项符合查询结果（耗时：0.0303秒） [XML]
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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Linq to Entities join vs groupjoin
...ies in the second list.
That's why Join is the equivalent of INNER JOIN in SQL: there are no entries for C. While GroupJoin is the equivalent of OUTER JOIN: C is in the result set, but with an empty list of related entries (in an SQL result set there would be a row C - null).
Syntax
So let the two l...
Django Setup Default Logging
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Tiny correction: the comment implies sql logging would be affected by the django.request logger. To redirect sql logging, you'd define a logger for 'django.db'. The django.request logger handles 5xx & 4xx http responses.
– rych
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XPath to select multiple tags
...in general people do care about the differences between: kitchen:table and sql:table, or between architecture:column, sql:column, array:column, military:column
– Dimitre Novatchev
Aug 1 '18 at 16:14
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Deep null checking, is there a better way?
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}
It's an idea I derrived from the null coalescing operator in C# and T-SQL. The nice thing is that the return type is always the return type of the inner property.
That way you can do this:
var berries = cake.Coal(x => x.frosting).Coal(x => x.berries);
...or a slight variation of the a...
How to work around the lack of transactions in MongoDB?
...know whether this comes from my limited viewpoint (I have only worked with SQL databases so far), or whether it actually can't be done.
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What is the most ridiculous pessimization you've seen? [closed]
... ad hoc Access connections to the production DB. Nothing like a few casual SQL'ers to forget a WHERE clause and deadlock the main tables!
– HardCode
Mar 28 '09 at 5:09
35
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Good MapReduce examples [closed]
... values and perform any sort of transformations on these.
For Example In SQL, Given the Date of Birth, to find out How many people are of age > 30 for a million records would take a while, and this would only increase in order of magnitute when the complexity of the query increases.
Map Reduce...
Rails: Default sort order for a rails model?
...efault_scope { order(created_at: :desc) } if, like me, you try to minimize sql syntax in rails.<br/>If you have multiple columns to order by and you want to use the new syntax you may need to wrap the desc columns in mustaches like this default_scope { order({begin_date: :desc}, :name) }
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