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What's the difference between TRUNCATE and DELETE in SQL
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General Overview
If you want to quickly delete all of the rows from a table, and you're really sure that you want to do it, and you do not have foreign keys against the tables, then a TRUNCATE is probably going to be faster than a DELETE.
Various system-specific issues have to be considered, a...
Generate GUID in MySQL for existing Data?
I've just imported a bunch of data to a MySQL table and I have a column "GUID" that I want to basically fill down all existing rows with new and unique random GUID's.
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Vertically align text next to an image?
...lt;/div>
Multiple-lines vertical-align:middle
<div style="display:table;width:30px;height:60px;">
<div style="display:table-cell;height:30px;">This is positioned in the middle</div>
</div>
If you must support ancient versions of IE <= 7
In order to get this to w...
Why should hash functions use a prime number modulus?
A long time ago, I bought a data structures book off the bargain table for $1.25. In it, the explanation for a hashing function said that it should ultimately mod by a prime number because of "the nature of math".
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SET versus SELECT when assigning variables?
... @var varchar(20)
set @var = 'Joe'
set @var = (select name from master.sys.tables where name = 'qwerty')
select @var /* @var is now NULL */
set @var = 'Joe'
select @var = name from master.sys.tables where name = 'qwerty'
select @var /* @var is still equal to 'Joe' */
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Why is SELECT * considered harmful?
...work. This is especially true when someone adds new columns to underlying tables that didn't exist and weren't needed when the original consumers coded their data access.
Indexing issues. Consider a scenario where you want to tune a query to a high level of performance. If you were to use *, and ...
SQL UPDATE SET one column to be equal to a value in a related table referenced by a different column
...ver MySQL. In my case, the source and destination columns are in the same table, but record selection is based on the other table. The "SELECT" version of the query works, but the UPDTATE statement throws a syntax error at "FROM"
– 2NinerRomeo
Mar 4 '15 at 19...
SQL DROP TABLE foreign key constraint
If I want to delete all the tables in my database like this, will it take care of the foreign key constraint? If not, how do I take care of that first?
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How to export table as CSV with headings on Postgresql?
I'm trying to export a PostgreSQL table with headings to a CSV file via command line, however I get it to export to CSV file, but without headings.
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What requests do browsers' “F5” and “Ctrl + F5” refreshes generate?
...trol by adding "Pragma: No-cache" when you pressed CTRL-F5.
Edit: Updated table
The table below is updated with information on what will happen when the browser's refresh-button is clicked (after a request by Joel Coehoorn), and the "max-age=0" Cache-control-header.
Updated table, 27 September 20...