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Why is there a difference in checking null against a value in VB.NET and C#?
...ditional advantage of mirroring the behaviour of NULL in (most if not all) SQL databases. This is also a more standard (than C#'s) interpretation of three-valued logic, as explained here.
The C# team made different assumptions about what NULL means, resulting in the behaviour difference you show. E...
JOIN queries vs multiple queries
...ou are joining 3 or more tables on different keys, often databases (i.e. mysql) can only use one index per table, meaning maybe one of the joins will be fast (and use an index) whereas the others will be extremely slow. For multiple queries, you can optimize the indexes to use for each query.
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Saving timestamp in mysql table using php
I have a field in a MySQL table which has a timestamp data type. I am saving data into that table. But when I pass the timestamp ( 1299762201428 ) to the record, it automatically saves the value 0000-00-00 00:00:00 into that table.
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Difference between Destroy and Delete
...sted). Returns the frozen instance.
The row is simply removed with an SQL DELETE statement on the record's primary key, and no callbacks are executed.
To enforce the object's before_destroy and after_destroy callbacks or any :dependent association options, use #destroy.
ActiveRecord::Pers...
Convert timestamp to date in MySQL query
I want to convert a timestamp in MySQL to a date.
10 Answers
10
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Storing DateTime (UTC) vs. storing DateTimeOffset
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Add Foreign Key to existing table
...n "SET FOREIGN_KEY_CHECKS=0;" before running the ADD CONSTRAINT command or SQL would complain "Cannot add or update a child row: a foreign key constraint fails".
– Erin Geyer
Mar 8 '17 at 13:03
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Modify table: How to change 'Allow Nulls' attribute from not null to allow null
How to change one attribute in a table using T-SQL to allow nulls (not null --> null)? Alter table maybe?
8 Answers
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NHibernate.MappingException: No persister for: XYZ
...guration..
If you're using app.config...
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<property name="show_sql">true</property>
<property name="query.substitutions">true 1, false 0, yes 'Y', no 'N'</property>
<mapping assembly="Project.DomainModel"/> <!-- Here -->
</session-factory>
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Give examples of functions which demonstrate covariance and contravariance in the cases of both over
...mparator<java.util.Date> { ... } and you want to sort a List<java.sql.Date> with that comparator (java.sql.Date is a sub-class of java.util.Date), you can do with:
<T> void sort(List<T> what, Comparator<? super T> how)
but not with
<T> void sort(List<T>...