大约有 40,000 项符合查询结果(耗时:0.0399秒) [XML]

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The type 'string' must be a non-nullable type in order to use it as parameter T in the generic type

Why do I get Error "The type 'string' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'System.Nullable'"? ...
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Sort ArrayList of custom Objects by property

... above the other answer is beyond me. This link may also be useful: Object Ordering Tutorial at Sun.com. – BalusC May 6 '10 at 21:26 ...
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select * vs select column

...as to what you want, it will first need to check the table's definition in order to determine the columns on that table. That lookup will cost some time - not much in a single query - but it adds up over time if you need only 2/3 of the columns, you're selecting 1/3 too much data which needs to be r...
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Should I return a Collection or a Stream?

... also some other cases that have good parallelization support, such as non-ordered generated streams (e.g., Stream.generate). However, where Streams is a poor fit is the reactive use case, where the data arrives with random latency. For that, I would suggest RxJava. – Brian G...
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Fast way of finding lines in one file that are not in another?

...by the scripts linked-to in Konsolebox's answer) which accepts arbitrarily ordered input files, and outputs the missing lines in the order they occur in file1. # output lines in file1 that are not in file2 BEGIN { FS="" } # preserve whitespace (NR==FNR) { ll1[FNR]=$0; nl1=FN...
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Why JSF calls getters multiple times

...public Boolean getGmapsAutoComplete() { switch (page) { case "/orders/pf_Add.xhtml": case "/orders/pf_Edit.xhtml": case "/orders/pf_EditDriverVehicles.xhtml": gmapsAutoComplete = true; break; default: gmapsAutoComplete = false; ...
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View's SELECT contains a subquery in the FROM clause

...y client_id create view view_credit_status as select credit_orders.client_id, sum(credit_orders.number_of_credits) as purchased, ifnull(t1.credits_used,0) as used from credit_orders left outer join view_clients_credit_usage as t1 on t1.client_id = credit_ord...
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When and why are database joins expensive?

... bulk disk reads which are the most expensive aspect of the exercise by an order of magnitude. Performing a join, by contrast, logically requires retrieval of only the keys. In practice, not even the key values are fetched: the key hash values are used for join comparisons, mitigating the cost of mu...
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Is recursion ever faster than looping?

...the best alternative is neither recursion nor iteration but instead higher order functions. These include "map", "filter", and "reduce" (which is also called "fold"). Not only are these the preferred style, not only are they often cleaner, but in some environments these functions are the first (or...
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What are the most common SQL anti-patterns? [closed]

...t *, you get whatever is in the table. Those columns may change names and order. Client code frequently relies on names and order. Every 6 months I'm asked how to preserve column order when modifying a table. If the rule was followed it wouldn't matter. – Amy B ...