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GROUP BY with MAX(DATE) [duplicate]
...ng to list the latest destination (MAX departure time) for each train in a table, for example :
6 Answers
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Reason for Column is invalid in the select list because it is not contained in either an aggregate f
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Suppose I have the following table T:
a b
--------
1 abc
1 def
1 ghi
2 jkl
2 mno
2 pqr
And I do the following query:
SELECT a, b
FROM T
GROUP BY a
The output should have two rows, one row where a=1 and a second row where a=2.
But wha...
Inserting multiple rows in a single SQL query? [duplicate]
I have multiple set of data to insert at once, say 4 rows. My table has three columns: Person , Id and Office .
4 Answe...
How can I retrieve Id of inserted entity using Entity framework? [closed]
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Let's consider the following scenario:table1 is supposed to generate an @@identity to use it in table2. Both table1 and table2 are supposed to be in the same transaction for e.g. one SaveChange operation must save both table's data. @@identity won't be generated ...
Entity Framework Code First - two Foreign Keys from same table
...his answer, however it makes the Foreign Key columns nullable in the Match table.
– RobHurd
Aug 21 '16 at 14:41
This w...
What are the options for storing hierarchical data in a relational database? [closed]
...useful for managing hierarchical data:
the HierarchyId data type.
common table expressions, using the with keyword.
Have a look at "Model Your Data Hierarchies With SQL Server 2008" by Kent Tegels on MSDN for starts. See also my own question: Recursive same-table query in SQL Server 2008
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SQL Server indexes - ascending or descending, what difference does it make?
...rily matters when used with composite indexes:
CREATE INDEX ix_index ON mytable (col1, col2 DESC);
can be used for either:
SELECT *
FROM mytable
ORDER BY
col1, col2 DESC
or:
SELECT *
FROM mytable
ORDER BY
col1 DESC, col2
, but not for:
SELECT *
FROM mytable
ORDE...
ActiveRecord OR query
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Use ARel
t = Post.arel_table
results = Post.where(
t[:author].eq("Someone").
or(t[:title].matches("%something%"))
)
The resulting SQL:
ree-1.8.7-2010.02 > puts Post.where(t[:author].eq("Someone").or(t[:title].matches("%something%"))).to_...
Change a column type from Date to DateTime during ROR migration
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First in your terminal:
rails g migration change_date_format_in_my_table
Then in your migration file:
For Rails >= 3.2:
class ChangeDateFormatInMyTable < ActiveRecord::Migration
def up
change_column :my_table, :my_column, :datetime
end
def down
change_column :my_tabl...
How should I store GUID in MySQL tables?
...the intention of representing said value with a value mapped from a lookup table (in most cases now, UTF8). A BINARY field expects the same kind of value without any intention of representing said data from a lookup table. I used CHAR(16) back in the 4.x days because back then MySQL wasn't as good a...