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Can hash tables really be O(1)?
It seems to be common knowledge that hash tables can achieve O(1), but that has never made sense to me. Can someone please explain it? Here are two situations that come to mind:
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Does MySQL index foreign key columns automatically?
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Yes, but only on innodb. Innodb is currently the only shipped table format that has foreign keys implemented.
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How To Change DataType of a DataColumn in a DataTable?
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You cannot change the DataType after the Datatable is filled with data. However, you can clone the Data table, change the column type and load data from previous data table to the cloned table as shown below.
DataTable dtCloned = dt.Clone();
dtCloned.Columns[0].DataTyp...
How can I SELECT rows with MAX(Column value), DISTINCT by another column in SQL?
My table is:
18 Answers
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Get table name by constraint name [duplicate]
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SELECT owner, table_name
FROM dba_constraints
WHERE constraint_name = <<your constraint name>>
will give you the name of the table. If you don't have access to the DBA_CONSTRAINTS view, ALL_CONSTRAINTS or USER_CONSTRAINTS...
Making a UITableView scroll when text field is selected
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If you use UITableViewController instead of UIViewController, it will automatically do so.
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When to use a “has_many :through” relation in Rails?
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# has attributes for date_joined and role
end
This introduces a new table, and eliminates the group_id column from the user's table.
The problem with this code is that you'd have to update every where else you use the user class and change it:
user.groups.first.name
# becomes
user.group_m...
Selecting data from two different servers in SQL Server
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You only have to set up one. Once you have that, you can call a table on the other server like so:
select
*
from
LocalTable,
[OtherServerName].[OtherDB].[dbo].[OtherTable]
Note that the owner isn't always dbo, so make sure to replace it with whatever schema you use.
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What's wrong with nullable columns in composite primary keys?
...n optionally be related to B, the clean solution is to create a resolution table (let's say AB). That table would link A with B: If there is a relationship then it would contain a record, if there isn't then it would not.
sh...
mysql Foreign key constraint is incorrectly formed error
I have two tables, table1 is the parent table with a column ID and table2 with a column IDFromTable1 (not the actual name) when I put a FK on IDFromTable1 to ID in table1 I get the error Foreign key constraint is incorrectly formed error . I would like to delete table 2 record if tab...