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How do MySQL indexes work?
...ically, how can they return the data requested without scanning the entire table?
8 Answers
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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 ...
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 to write the Fibonacci Sequence?
...bject every time the function is called, but normally you wouldn't use a mutable default argument for exactly this reason):
def mem_fib(n, _cache={}):
'''efficiently memoized recursive function, returns a Fibonacci number'''
if n in _cache:
return _cache[n]
elif n > 1:
...
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...
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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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...
Building a notification system [closed]
...this topic is already quite old, however i'm a bit puzzled about the first table, what excactly is the purpose of this table? what is the advantage of having this as a separate table versus putting the userID in the notification_object table? In other words when will you create a new entry in notifi...
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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