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How to create GUID / UUID?
...ulnerabilities. Either way, if it's a random number ID that's going into a table, I would probably be generating it server-side, so that I know I have control over the process.
– Cam Jackson
Nov 1 '12 at 14:34
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What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do
...this option is used it does not drop the whole schema instead it drops the tables whose mappings are available while running this. For example if a database with Schema S has A, B, C tables and java code has mappings for A and B only then Hibernate will not drop the table C.
– ...
What's the difference between VARCHAR and CHAR?
...: when Anon. says "your content is a fixed size" it means the rows of your table must contain all fixed size fields. You get no performance improvement if you use CHAR against VARCHAR in one field, but the table contains other fields that are VARCHAR.
– Marco Demaio
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How to read a .xlsx file using the pandas Library in iPython?
... file using the Pandas Library of python and port the data to a postgreSQL table.
6 Answers
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Update or Insert (multiple rows and columns) from subquery in PostgreSQL
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For the UPDATE
Use:
UPDATE table1
SET col1 = othertable.col2,
col2 = othertable.col3
FROM othertable
WHERE othertable.col1 = 123;
For the INSERT
Use:
INSERT INTO table1 (col1, col2)
SELECT col1, col2
FROM othertable
You don't ...
Fast permutation -> number -> permutation mapping algorithms
... brought down to n*log(n), see section 10.1.1
("The Lehmer code (inversion table)", p.232ff) of the fxtbook:
http://www.jjj.de/fxt/#fxtbook
skip to section 10.1.1.1 ("Computation with large arrays" p.235) for the fast method.
The (GPLed, C++) code is on the same web page.
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How to return only the Date from a SQL Server DateTime datatype
...PU time taken to perform all the pieces. If both queries are run against a table with millions of rows, the CPU time using DateDiff can be close to 1/3rd of the Convert CPU time!
To see execution plans for queries:
set showplan_text on
GO
Both DATEADD and DATEDIFF will execute a CONVERT_IMPLICI...
How does Google's Page Speed lossless image compression work?
...bilities to the fullest, e.g. PNG8+a instead of PNG24+a, optimized Huffman tables in JPEG, etc.
Photoshop doesn't really try hard to do that when saving images for the web, so it's not surprising that any tool beats it.
See
ImageOptim (lossless) and
ImageAlpha (lossy) for smaller PNG files (hi...
How should I choose an authentication library for CodeIgniter? [closed]
... set
Very good documentation
Simple and elegant database design (just 4 DB tables)
Most features are optional and easily configured
Language file support
reCAPTCHA supported
Hooks into CI's validation system
Activation emails
Login with email, username or both (configurable)
Unactivated accounts aut...
What is the purpose of Order By 1 in SQL select statement?
...relation names are allowed in the OREDER BY clause because, in theory, the table correlation names are out of scope i.e. should be ORDER BY PAYMENT_DATE;. Of course, not all SQL implementations conform to Standards.
– onedaywhen
Aug 10 '10 at 7:17
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