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• How can I get a COUNT(col) ... GROUP BY to use an index?

  - by thecoop

  I've got a table (col1, col2, ...) with an index on (col1, col2, ...). The table has got millions of rows in it, and I want to run a query: SELECT col1, COUNT(col2) WHERE col1 NOT IN (<couple of exclusions>) GROUP BY col1 Unfortunately, this is resulting in a full table scan of the table, which takes upwards of a minute. Is there any way of getting oracle to use the index on the columns to return the results much faster?

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• Thin down jQuery

  - by Taylor Satula

  Hi, I have been optimizing my website but the one problem that stands in my way is all the jQuery functions that I do not use. The only ones that I use are for a smooth page scroller. It just seems like such a waste of download time. My question is: Is there any script or program that will remove the jQuery code that I do not need and leave the 1 or 2 functions that I do need.

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• Whether to put method code in a VB.Net data storage class, or put it in a separate class?

  - by Alan K

  TLDR summary: (a) Should I include (lengthy) method code in classes which may spawn multiple objects at runtime, (b) does doing so cause memory usage bloat, (c) if so should I "outsource" the code to a class that is loaded only once and have the class methods call that, or alternatively (d) does the code get loaded only once with the object definition anyway and I'm worrying about nothing? ........ I don't know whether there's a good answer to this but if there is I haven't found it yet by searching in the usual places. In my VB.Net (2010 if it matters) WinForms project I have about a dozen or so class objects in an object model. Some of these are pretty simple and do little more than act as data storage repositories. The ones further up the object model, however, have an increasing number of methods. There can be a significant number of higher level objects in use though the exact number will be runtime dependent so I can't be more precise than that. As I was writing the method code for one of the top level ones I noticed that it was starting to get quite lengthy. Memory optimisation is something of a lost art given how much memory the average PC has these days but I don't want to make my application a resource hog. So my questions for anyone who knows .Net way better than I do (of which there will be many) are: Is the code loaded into memory with each instance of the class that's created? Alternatively is it loaded only once with the definition of the class, and all derived objects just refer to that definition? (I'm not really sure how that could be possible given that, for example, event handlers can be assigned dynamically, but no harm asking.) If the answer to the first one is yes, would it be more efficient to write the code in a "utility" object which is loaded only once and called from the real class' methods? Any thoughts appreciated.

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• Use C function in C++ program; "multiply-defined" error

  - by eom

  I am trying to use this code for the Porter stemming algorithm in a C++ program I've already written. I followed the instructions near the end of the file for using the code as a separate module. I created a file, stem.c, that ends after the definition and has extern int stem(char * p, int i, int j) ... It worked fine in Xcode but it does not work for me on Unix with gcc 4.1.1--strange because usually I have no problem moving between the two. I get the error ld: fatal: symbol `stem(char*, int, int)' is multiply-defined: (file /var/tmp//ccrWWlnb.o type=FUNC; file /var/tmp//cc6rUXka.o type=FUNC); ld: fatal: File processing errors. No output written to cluster I've looked online and it seems like there are many things I could have wrong, but I'm not sure what combination of a header file, extern "C", etc. would work.

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• Creating objects makes the VM faster?

  - by Sudhir Jonathan

  Look at this piece of code: MessageParser parser = new MessageParser(); for (int i = 0; i < 10000; i++) { parser.parse(plainMessage, user); } For some reason, it runs SLOWER (by about 100ms) than for (int i = 0; i < 10000; i++) { MessageParser parser = new MessageParser(); parser.parse(plainMessage, user); } Any ideas why? The tests were repeated a lot of times, so it wasn't just random. How could creating an object 10000 times be faster than creating it once?

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• How can a language be interpreted by itself (like Rubinius)?

  - by japancheese

  I've been programming in Ruby for a while now with just the standard MRI implementation of Ruby, but I've always been curious about the other implementations I hear so much about. I was reading about Rubinius the other day, a Ruby interpreter written in Ruby. I tried looking it up in various places, but I was having a hard time figuring out exactly how something like this works. I've never had much experience in compilers or language writing but I'm really interested to figure it out. How exactly can a language be interpreted by itself? Is there a basic step in compiling that I don't understand where this makes sense? Can someone explain this to me like I'm an idiot (because that wouldn't be too far off base anyways)

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• Custom Output => List of Errors interpretation in VS2008 IDE.

  - by Hamish Grubijan

  Hello, I have a "database solution" project in VS2008 - it generates SQL for more than one DB vendor from some sort of templates. In order to save time, I also have a tool in VS2008 configured (a Python script), which can compile an individual stored procedure. Now, with the Python script I have the freedom of processing the output and have it take on whatever form I want. I am toying with an idea of having these errors and warnings somehow recognized and populating the click-able Error / Warning list. This is what a typical Oracle error looks like: LINE/COL ERROR -------- ----------------------------------------------------------------- 324/5 PL/SQL: Statement ignored 324/82 PLS-00363: expression 'VSOURCE_SYSTEM_ID' cannot be used as an assignment target Warning: Procedure created with compilation errors. PROCEDURE: ADD_PROPOSED error on creation Errors for PROCEDURE ADD_PROPOSED: LINE/COL ERROR This might be a long shot, but it is worthwhile for me. I do this stuff a lot. Thank you!

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• How to execute machine language from memory?

  - by Mike Curry

  I wrote a program to compile a simple text program to a compiled executable... Is it possible that I can load an executable to memory an some how point a pc counter to the memory space at will? Here is what I made that I would like to store the programs to memory for execution on demand... Kind of wanting to make a little web language like php but compile it... Just for learning. http://spiceycurry.blogspot.com/2010/05/simple-compilable-programming-language.html

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• Execute a method less times possible - PHP

  - by serhio

  I have a site in multiple languages. I have a method that returns me the today currencies in a array. I display that currencies in a table then. // --- en/index.php <?php include_once "../exchangeRates.php"; $currencies = ReadExchangeRates(); // --- fr/index.php <?php include_once "../exchangeRates.php"; $currencies = ReadExchangeRates(); ... // somewhere in the page <td><?php echo $currencies["eur"]["today"]; ?></td> So, every time I load, en/ or fr/ or other language, I request the exchange rates from a external site. Can I optimize this behavior (reading once per day or session)? maybe to store a global variable and check the update date?

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• Solving C++ 'target of assignment not really an lvalue' errors

  - by Jason

  Given this code: void FrMemCopy(void *to, const void *from, size_t sz) { size_t sz8 = sz >> 3; size_t sz1 = sz - (sz8 << 3); while (sz8-- != 0) { *((double *)to)++ = *((double *)from)++; } while (sz1-- != 0) { *((char *)to)++ = *((char *)from)++; } } I am receiving target of assignment not really an lvalue warnings on the 2 lines inside the while loops. Can anyone break down those lines? a cast then an increment? What is a simplier way to write that? What does the error mean?

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• Ternary Operators in JavaScript Without an "Else"

  - by Oscar Godson

  I've been using them forever, and I love them. To me they see cleaner and i can scan faster, but ever since I've been using them i've always had to put null in the else conditions that don't have anything. Is there anyway around it? E.g. condition ? x=true : null ; basically, is there a way to do: condition ? x=true; Now it shows up as a syntax error...

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• Visual Studio: how does VS decide to build a release or debug exe

  - by Snake

  Hi, I just created a new project configuration. I named it 'Blah' So no 'debug' in it. Now how does Visual Studio know when to compile a debug file or a release file. is this merely defined by the DEBUG constant? Or am I wrong? :) Thanks

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• how to avoid temporaries when copying weakly typed object

  - by Truncheon

  Hi. I'm writing a series classes that inherit from a base class using virtual. They are INT, FLOAT and STRING objects that I want to use in a scripting language. I'm trying to implement weak typing, but I don't want STRING objects to return copies of themselves when used in the following way (instead I would prefer to have a reference returned which can be used in copying): a = "hello "; b = "world"; c = a + b; I have written the following code as a mock example: #include <iostream> #include <string> #include <cstdio> #include <cstdlib> std::string dummy("<int object cannot return string reference>"); struct BaseImpl { virtual bool is_string() = 0; virtual int get_int() = 0; virtual std::string get_string_copy() = 0; virtual std::string const& get_string_ref() = 0; }; struct INT : BaseImpl { int value; INT(int i = 0) : value(i) { std::cout << "constructor called\n"; } INT(BaseImpl& that) : value(that.get_int()) { std::cout << "copy constructor called\n"; } bool is_string() { return false; } int get_int() { return value; } std::string get_string_copy() { char buf[33]; sprintf(buf, "%i", value); return buf; } std::string const& get_string_ref() { return dummy; } }; struct STRING : BaseImpl { std::string value; STRING(std::string s = "") : value(s) { std::cout << "constructor called\n"; } STRING(BaseImpl& that) { if (that.is_string()) value = that.get_string_ref(); else value = that.get_string_copy(); std::cout << "copy constructor called\n"; } bool is_string() { return true; } int get_int() { return atoi(value.c_str()); } std::string get_string_copy() { return value; } std::string const& get_string_ref() { return value; } }; struct Base { BaseImpl* impl; Base(BaseImpl* p = 0) : impl(p) {} ~Base() { delete impl; } }; int main() { Base b1(new INT(1)); Base b2(new STRING("Hello world")); Base b3(new INT(*b1.impl)); Base b4(new STRING(*b2.impl)); std::cout << "\n"; std::cout << b1.impl->get_int() << "\n"; std::cout << b2.impl->get_int() << "\n"; std::cout << b3.impl->get_int() << "\n"; std::cout << b4.impl->get_int() << "\n"; std::cout << "\n"; std::cout << b1.impl->get_string_ref() << "\n"; std::cout << b2.impl->get_string_ref() << "\n"; std::cout << b3.impl->get_string_ref() << "\n"; std::cout << b4.impl->get_string_ref() << "\n"; std::cout << "\n"; std::cout << b1.impl->get_string_copy() << "\n"; std::cout << b2.impl->get_string_copy() << "\n"; std::cout << b3.impl->get_string_copy() << "\n"; std::cout << b4.impl->get_string_copy() << "\n"; return 0; } It was necessary to add an if check in the STRING class to determine whether its safe to request a reference instead of a copy: Script code: a = "test"; b = a; c = 1; d = "" + c; /* not safe to request reference by standard */ C++ code: STRING(BaseImpl& that) { if (that.is_string()) value = that.get_string_ref(); else value = that.get_string_copy(); std::cout << "copy constructor called\n"; } If was hoping there's a way of moving that if check into compile time, rather than run time.

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• I'm doing a lot of lists and dictionary sorting...and this is causing memory errors in Python websit

  - by alex

  I retrieved data from the log table in my database. Then I started finding unique users, comparing/sorting lists, etc. In the end I got down to this. stats = {'2010-03-19': {'date': '2010-03-19', 'unique_users': 312, 'queries': 1465}, '2010-03-18': {'date': '2010-03-18', 'unique_users': 329, 'queries': 1659}, '2010-03-17': {'date': '2010-03-17', 'unique_users': 379, 'queries': 1845}, '2010-03-16': {'date': '2010-03-16', 'unique_users': 434, 'queries': 2336}, '2010-03-15': {'date': '2010-03-15', 'unique_users': 390, 'queries': 2138}, '2010-03-14': {'date': '2010-03-14', 'unique_users': 460, 'queries': 2221}, '2010-03-13': {'date': '2010-03-13', 'unique_users': 507, 'queries': 2242}, '2010-03-12': {'date': '2010-03-12', 'unique_users': 629, 'queries': 3523}, '2010-03-11': {'date': '2010-03-11', 'unique_users': 811, 'queries': 4274}, '2010-03-10': {'date': '2010-03-10', 'unique_users': 171, 'queries': 1297}, '2010-03-26': {'date': '2010-03-26', 'unique_users': 299, 'queries': 1617}, '2010-03-27': {'date': '2010-03-27', 'unique_users': 323, 'queries': 1310}, '2010-03-24': {'date': '2010-03-24', 'unique_users': 352, 'queries': 2112}, '2010-03-25': {'date': '2010-03-25', 'unique_users': 330, 'queries': 1290}, '2010-03-22': {'date': '2010-03-22', 'unique_users': 329, 'queries': 1798}, '2010-03-23': {'date': '2010-03-23', 'unique_users': 329, 'queries': 1857}, '2010-03-20': {'date': '2010-03-20', 'unique_users': 368, 'queries': 1693}, '2010-03-21': {'date': '2010-03-21', 'unique_users': 329, 'queries': 1511}, '2010-03-29': {'date': '2010-03-29', 'unique_users': 325, 'queries': 1718}, '2010-03-28': {'date': '2010-03-28', 'unique_users': 340, 'queries': 1815}, '2010-03-30': {'date': '2010-03-30', 'unique_users': 329, 'queries': 1891}} It's not a big dictionary. But when I try to do one last thing...it craps out on me. for k, v in stats: mylist.append(v) too many values to unpack What the heck does that mean??? TOO MANY VALUES TO UNPACK.

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• Anything wrong with this MySQL quert? takes 10 seconds+ to load

  - by user345426

  I have a search that is taking 10 seconds+ to execute! Keep in mind it is also searching over 200,000 products in the database. I posted the explain and MySQL query here. 1 SIMPLE p ref PRIMARY,products_status,prod_prodid_status,product... products_status 1 const 9048 Using where; Using temporary; Using filesort 1 SIMPLE v ref PRIMARY,vendors_id,vendors_vendorid vendors_vendorid 4 rhinomar_rhinomartnew.p.vendors_id 1 1 SIMPLE s ref products_id products_id 4 rhinomar_rhinomartnew.p.products_id 1 1 SIMPLE pd ref PRIMARY,products,prod_desc_prodid_prodname prod_desc_prodid_prodname 4 rhinomar_rhinomartnew.p.products_id 1 1 SIMPLE p2c ref PRIMARY,ptc_catidx PRIMARY 4 rhinomar_rhinomartnew.p.products_id 1 Using where; Using index 1 SIMPLE c eq_ref PRIMARY PRIMARY 4 rhinomar_rhinomartnew.p2c.categories_id 1 Using where MySQL Query: select p.products_id, p.products_image, p.products_price, p.products_weight, p.products_unit_quantity, s.specials_new_products_price, s.status, pd.products_name, pd.products_img_alt from products p left join vendors v ON v.vendors_id = p.vendors_id left join specials s on s.products_id = p.products_id left join products_description pd on pd.products_id = p.products_id left join products_to_categories p2c on p2c.products_id = p.products_id left join categories c on c.categories_id = p2c.categories_id where ( ( pd.products_name like '%apparel%' ) or p2c.categories_id IN (773, 132, 135, 136, 119, 122, 124, 125, 126, 1749, 1753, 1747, 123, 127, 130, 131, 178, 137, 140, 164, 165, 166, 167, 168, 169, 832, 2045 ) or p.products_id = 'apparel' or p.products_model = 'apparel' or CONCAT(v.vendors_prefix, '-') = 'apparel' or CONCAT( v.vendors_prefix, '-', p.products_id ) = 'apparel' ) and p.products_status = '1' and c.categories_status = '1' group by p.products_id order by pd.products_name

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• how to use cpp source for 2 projects

  - by joels

  I'm not sure if I am going about this the right way. I am making some c++ classes to use in 2 apps. I am going to have to compile them to be used in a Cocoa app and later be compiled for use with fastcgi. Should I create a dynamic library?

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• Xcode: Is there a location/flag to prevent a Class from compiling?

  - by Meltemi

  Is there a place (or flag) in Xcode for files that you don't want to compile? There are some classes that are/may become part of a project but currently won't compile. The main project doesn't link to them but Xcode still tries to compile them. Is there a way to prevent blocking the rest of project from compiling until these new Classes are "ready"?

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• Scala unsatisfiable cyclic dependency in "table-layout" library (Toolkit class)

  - by Atol

  When I try to compile with sbt some code containing an instance of a Table from this library I get this error: java.lang.AssertionError: assertion failed: unsatisfiable cyclic dependency in 'class Toolkit' It seems to work with Java so I don't understand why it fails in Scala. Here is the toolkit class: http://code.google.com/p/table-layout/source/browse/branches/v1/tablelayout/src/com/esotericsoftware/tablelayout/Toolkit.java As long as I get this error I'm totally stopped in my project :(.

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• Which is faster in memory, ints or chars? And file-mapping or chunk reading?

  - by Nick

  Okay, so I've written a (rather unoptimized) program before to encode images to JPEGs, however, now I am working with MPEG-2 transport streams and the H.264 encoded video within them. Before I dive into programming all of this, I am curious what the fastest way to deal with the actual file is. Currently I am file-mapping the .mts file into memory to work on it, although I am not sure if it would be faster to (for example) read 100 MB of the file into memory in chunks and deal with it that way. These files require a lot of bit-shifting and such to read flags, so I am wondering that when I reference some of the memory if it is faster to read 4 bytes at once as an integer or 1 byte as a character. I thought I read somewhere that x86 processors are optimized to a 4-byte granularity, but I'm not sure if this is true... Thanks!

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• Fast find object by string property

  - by Andrew Kalashnikov

  Hello, colleagues. I've got task to fast find object by its string property. Object: class DicDomain { public virtual string Id{ get; set; } public virtual string Name { get; set; } } For storing my object I use List[T] dictionary where T is DicDomain for now . I've got 5-10 such lists, which contain about 500-20000 at each one. Task is find objects by its Name. I use next code now: List<T> entities = dictionary.FindAll(s => s.Name.Equals(word, StringComparison.OrdinalIgnoreCase)); I've got some questions: Is my search speed optimal. I think now. Data structure. It List good for this task. What about hashtable,sorted... Method Find. May be i should use string intern?? I haven't much exp at these tasks. Can u give me good advice for increase perfomance. Thanks

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• Iterative Reduction to Null Matrix

  - by user1459032

  Here's the problem: I'm given a matrix like Input: 1 1 1 1 1 1 1 1 1 At each step, I need to find a "second" matrix of 1's and 0's with no two 1's on the same row or column. Then, I'll subtract the second matrix from the original matrix. I will repeat the process until I get a matrix with all 0's. Furthermore, I need to take the least possible number of steps. I need to print all the "second" matrices in O(n) time. In the above example I can get to the null matrix in 3 steps by subtracting these three matrices in order: Expected output: 1 0 0 0 1 0 0 0 1 0 0 1 1 0 0 0 1 0 0 1 0 0 0 1 1 0 0 I have coded an attempt, in which I am finding the first maximum value and creating the second matrices based on the index of that value. But for the above input I am getting 4 output matrices, which is wrong: My output: 1 0 0 0 1 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 My solution works for most of the test cases but fails for the one given above. Can someone give me some pointers on how to proceed, or find an algorithm that guarantees optimality? Test case that works: Input: 0 2 1 0 0 0 3 0 0 Output 0 1 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0

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• Which way to store this data is effective?

  - by Tattat

  I am writing a game, which need a map, and I want to store the map. The first thing I can think of, is using a 2D-array. But the problem is what data should I store in the 2D-array. The player can tap different place to have different reaction. So, I am thinking store a 2D-array with objects, when player click some position, and I find it in the array, and use the object in that array to execute a cmd. But I have a concern that storing lots of object may use lots of memory. So, I am think storing char/int only. But it seems that not enough for me. I want to store the data like that: { Type:1 Color:Green } No matter what color is, if they are all type 1, the have same reactions in logic, but the visual effect is based on the color. So, it is not easy to store using a prue char/int data, unless I make something like this: 1-5 --> all type 1. 1=color green , 2=color red, 3 = color yellow.... ... 6-10 --> all type 2. 2 = color green, 2 = color red ... ... So, do you have any ideas on how to minimize the ram use, but also easy for me to read... ...thx

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• Scalably processing large amount of comlpicated database data in PHP, many times a day.

  - by Eph

  I'm soon to be working on a project that poses a problem for me. It's going to require, at regular intervals throughout the day, processing tens of thousands of records, potentially over a million. Processing is going to involve several (potentially complicated) formulas and the generation of several random factors, writing some new data to a separate table, and updating the original records with some results. This needs to occur for all records, ideally, every three hours. Each new user to the site will be adding between 50 and 500 records that need to be processed in such a fashion, so the number will not be steady. The code hasn't been written, yet, as I'm still in the design process, mostly because of this issue. I know I'm going to need to use cron jobs, but I'm concerned that processing records of this size may cause the site to freeze up, perform slowly, or just piss off my hosting company every three hours. I'd like to know if anyone has any experience or tips on similar subjects? I've never worked at this magnitude before, and for all I know, this will be trivial to the server and not pose much of an issue. As long as ALL records are processed before the next three hour period occurs, I don't care if they aren't processed simultaneously (though, ideally, all records belonging to a specific user should be processed in the same batch), so I've been wondering if I should process in batches every 5 minutes, 15 minutes, hour, whatever works, and how best to approach this (and make it scalable in a way that is fair to all users)?

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• MySQL query paralyzes site

  - by nute

  Once in a while, at random intervals, our website gets completely paralyzed. Looking at SHOW FULL PROCESSLIST;, I've noticed that when this happens, there is a specific query that is "Copying to tmp table" for a loooong time (sometimes 350 seconds), and almost all the other queries are "Locked". The part I don't understand is that 90% of the time, this query runs fine. I see it going through in the process list and it finishes pretty quickly most of the time. This query is being called by an ajax call on our homepage to display product recommendations based your browsing history (a la amazon). Just sometimes, randomly (but too often), it gets stuck at "copying to tmp table". Here is a caught instance of the query that was up 109 seconds when I looked: SELECT DISTINCT product_product.id, product_product.name, product_product.retailprice, product_product.imageurl, product_product.thumbnailurl, product_product.msrp FROM product_product, product_xref, product_viewhistory WHERE ( (product_viewhistory.productId = product_xref.product_id_1 AND product_xref.product_id_2 = product_product.id) OR (product_viewhistory.productId = product_xref.product_id_2 AND product_xref.product_id_1 = product_product.id) ) AND product_product.outofstock='N' AND product_viewhistory.cookieId = '188af1efad392c2adf82' AND product_viewhistory.productId IN (24976, 25873, 26067, 26073, 44949, 16209, 70528, 69784, 75171, 75172) ORDER BY product_xref.hits DESC LIMIT 10 Of course the "cookieId" and the list of "productId" changes dynamically depending on the request. I use php with PDO.

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• MySQL Datefields: duplicate or calculate?

  - by Konerak

  We are using a table with a structure imposed upon us more than 10 years ago. We are allowed to add columns, but urged not to change existing columns. Certain columns are meant to represent dates, but are put in different format. Amongst others: * CHAR(6): YYMMDD * CHAR(6): DDMMYY * CHAR(8): YYYYMMDD * CHAR(8): DDMMYYYY * DATE * DATETIME Since we now would like to do some more complex queries, using advanced date functions, my manager proposed to d*uplicate those problem columns* to a proper FORMATTED_OLDCOLUMNNAME column using a DATE or DATETIME format. Is this the way to go? Couldn't we just use the STR_TO_DATE function each time we accessed the columns? To avoid every query having to copy-paste the function, I could still work with a view or a stored procedure, but duplicating data to avoid recalculation sounds wrong. Solutions I see (I guess I prefer 2.2.1) 1. Physically duplicate columns 1.1 In the same table 1.1.1 Added by each script that does a modification (INSERT/UPDATE/REPLACE/...) 1.1.2 Maintained by a trigger on each modification 1.2 In a separate table 1.2.1 Added by each script that does a modification (INSERT/UPDATE/REPLACE/...) 1.2.2 Maintained by a trigger on each modification 2. On-demand transformation 2.1 Each query has to perform the transformation 2.1.1 Using copy-paste in the source code 2.1.2 Using a library 2.1.3 Using a STORED PROCEDURE 2.2 A view performs the transformation 2.2.1 A separate table replacing the entire table 2.2.2 A separate table just adding the date-fields for the primary keys Am I right to say it's better to recalculate than to store? And would a view be a good solution?

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