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How to import multiple .csv files at once?
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+1 seems like producing a single data frame -- the SQL UNION of all CSV files -- is the easiest to work with. Since OP didn't specify whether they want 1 data frame or many data frames, I assumed 1 data frame is best, so I am surprised the accepted answer does not do any of the "...
Why does Oracle 9i treat an empty string as NULL?
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@sehe the confusing bit for me is select 1 from dual where ('' is null)
– matt freake
Aug 22 '13 at 15:58
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Condition within JOIN or WHERE
...of filtering criteria more easily maintainable.
For example, instead of:
SELECT *
FROM Customers c
INNER JOIN CustomerAccounts ca
ON ca.CustomerID = c.CustomerID
AND c.State = 'NY'
INNER JOIN Accounts a
ON ca.AccountID = a.AccountID
AND a.Status = 1
Write:
SELECT *
FROM Customer...
How important is the order of columns in indexes?
I've heard that you should put columns that will be the most selective at the beginning of the index declaration. Example:
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Getting the difference between two sets
...ork but I think it would be a nice feature to have the set operations like union , difference built in java. The above solution will modify the set , in many situations we don't really want that.
– Praveen Kumar
Jul 18 '14 at 8:09
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Check if a temporary table exists and delete if it exists before creating a temporary table
...me in SQL Server 2005, with the extra "foo" column appearing in the second select result:
IF OBJECT_ID('tempdb..#Results') IS NOT NULL DROP TABLE #Results
GO
CREATE TABLE #Results ( Company CHAR(3), StepId TINYINT, FieldId TINYINT )
GO
select company, stepid, fieldid from #Results
GO
ALTER TABLE #R...
How to define a preprocessor symbol in Xcode
...ur Target or Project settings, click the Gear icon at the bottom left, and select "Add User-Defined Setting". The new setting name should be GCC_PREPROCESSOR_DEFINITIONS, and you can type your definitions in the right-hand field.
Per Steph's comments, the full syntax is:
constant_1=VALUE constant_...
Unicode Processing in C++
...ng new projects in Dev Studio, religiously make sure the Unicode option is selected in your project properties.
For C++ strings, use std::wstring instead of std::string
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improve this answer
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Emacs bulk indent for Python
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I use the following snippet. On tab when the selection is inactive, it indents the current line (as it normally does); when the selection is inactive, it indents the whole region to the right.
(defun my-python-tab-command (&optional _)
"If the region is active, s...
VC DDE（Dynamic Data Exchange）与EXCEL连接 - C/C++ - 清泛网 - 专注C/C++及内核技术
...char szItem5[] = "R3C1"; char szData5[16] = "0";
//char szCmd2[] = "[SELECT(\"R3C1\")][FONT.PROPERTIES(,\"Bold\")][SAVE()][QUIT()]";
char szCmd2[] = "[SELECT(\"R3C1\")][FONT.PROPERTIES(,\"Bold\")]";
char szCmd3[] = "[SELECT(\"R3C1\")][FONT.PROPERTIES(,\"Bold\")]";
int i,j,k;
char...