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Why is LINQ JOIN so much faster than linking with WHERE?
...nce they work directly in memory (Linq to DataSet)
The query with multiple tables and a Where condition actually performs a cartesian product of all the tables, then filters the rows that satisfy the condition. This means the Where condition is evaluated for each combination of rows (n1 * n2 * n3 * ...
How can I rename a field for all documents in MongoDB?
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For some reason, this didn't work for me when I used the "table.field" : "table.field" syntax. It did work when I just used the "field" : "field" syntax.
– Ben
Sep 2 '15 at 0:21
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Using backticks around field names
...r field` , `field,with,comma`
Which does of course generate badly named tables.
If you're just being concise I don't see a problem with it,
you'll note if you run your query as such
EXPLAIN EXTENDED Select foo,bar,baz
The generated warning that comes back will have back-ticks and fully qua...
Error in finding last used cell in Excel with VBA
...ow
Else
lastrow = 1
End If
End With
Find Last Row in a Table (ListObject)
The same principles apply, for example to get the last row in the third column of a table:
Sub FindLastRowInExcelTableColAandB()
Dim lastRow As Long
Dim ws As Worksheet, tbl as ListObject
Set ws = Sheets(...
Understanding garbage collection in .NET
...ow. The second duty is however completely invisible. It also generates a table that describes how the local variables inside the method body are used. That table has an entry for each method argument and local variable with two addresses. The address where the variable will first store an object ...
Compare two MySQL databases [closed]
... sets, etc. mysqldump --opt --compact --skip-extended-insert -u user -p db table > file.sql
– zanlok
Mar 6 '12 at 21:53
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Count number of rows within each group
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An old question without a data.table solution. So here goes...
Using .N
library(data.table)
DT <- data.table(df)
DT[, .N, by = list(year, month)]
share
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Remove specific characters from a string in Python
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Strings in Python are immutable (can't be changed). Because of this, the effect of line.replace(...) is just to create a new string, rather than changing the old one. You need to rebind (assign) it to line in order to have that variable take the new...
Finding duplicate values in a SQL table
...till requires all non-aggregated columns in the GROUP BY.
MySQL is unpredictable and you need sql_mode=only_full_group_by:
GROUP BY lname ORDER BY showing wrong results;
Which is the least expensive aggregate function in the absence of ANY() (see comments in accepted answer).
Oracle isn't mainstr...
T-SQL: Deleting all duplicate rows but keeping one [duplicate]
I have a table with a very large amount of rows. Duplicates are not allowed but due to a problem with how the rows were created I know there are some duplicates in this table.
I need to eliminate the extra rows from the perspective of the key columns. Some other columns may have slightly different...