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  • Compound IDENTITY column in SQL SERVER 2008

    - by Asaf R
    An Orders table has a CustomerId column and an OrderId column. For certain reasons it's important that OrderId is no longer than 2-bytes. There will be several million orders in total, which makes 2-bytes not enough. A customer will have no more than several thousand orders making 2-bytes enough. The obvious solution is to have the (CustomerId, OrderId) be unique rather than (OrderId) itself. The problem is generating the next Customer's OrderId. Preferably, without creating a separate table for each customer (even if it contains only an IDENTITY column), in order to keep the upper layers of the solution simple. Q: how would you generate the next OrderId so that (CustomerId, OrderId) is unique but OrderId itself is allowed to have repetitions? Does Sql Server 2008 have a built in functionality for doing this? For lack of a better term I'm calling it a Compound IDENTITY column.

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  • Detect block size for quota in Linux

    - by Chen Levy
    The limit placed on disk quota in Linux is counted in blocks. However, I found no reliable way to determine the block size. Tutorials I found refer to block size as 512 bytes, and sometimes as 1024 bytes. I got confused reading a post on LinuxForum.org for what a block size really means. So I tried to find that meaning in the context of quota. I found a "Determine the block size on hard disk filesystem for disk quota" tip on NixCraft, that suggested the command: dumpe2fs /dev/sdXN | grep -i 'Block size' or blockdev --getbsz /dev/sdXN But on my system those commands returned 4096, and when I checked the real quota block size on the same system, I got a block size of 1024 bytes. Is there a scriptable way to determine the quota block size on a device, short of creating a known sized file, and checking it's quota usage?

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  • RSA public key exportation

    - by user308806
    Dear all, Here is my code KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA"); KeyPair myPair = kpg.generateKeyPair(); PrivateKey k = myPair.getPrivate(); System.out.print(k.serialVersionUID); Cipher c = Cipher.getInstance("RSA"); c.init(Cipher.ENCRYPT_MODE, myPair.getPublic()); String myMessage = new String("Testing the message"); byte[] bytes = c.doFinal(myMessage.getBytes()); String tt = new String(bytes); System.out.println(tt); Cipher d = Cipher.getInstance("RSA"); d.init(Cipher.DECRYPT_MODE, myPair.getPrivate()); byte[] temp = d.doFinal(bytes); String tst = new String(temp); System.out.println(tst); My question is how can i get the public key and stored elsewhere

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  • Question About MP4(AAC) Binary Tree

    - by DeanMc
    I'm in the very early stages of working on a tag editor for mp4 files and more specifically iTunes AAC ones. After doing some snooping around it seems that the file's structure is not as complicated as I first thought and is built in a sort of tree like the following 4 Bytes [Atom Length] 4 Bytes [Atom Name] X Bytes [Atom Data] An atom's data is as large as the length and can contain either Data(information) or another atom. What I am trying to work out is how one determines if the data is information or an actual atom. Any insight would be much appreciated.

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  • In Haskell, will calling length on a Lazy ByteString force the entire string into memory?

    - by me2
    I am reading a large data stream using lazy bytestrings, and want to know if at least X more bytes is available while parsing it. That is, I want to know if the bytestring is at least X bytes long. Will calling length on it result in the entire stream getting loaded, hence defeating the purpose of using the lazy bytestring? If yes, then the followup would be: How to tell if it has at least X bytes without loading the entire stream? EDIT: Originally I asked in the context of reading files but understand that there are better ways to determine filesize. Te ultimate solution I need however should not depend on the lazy bytestring source.

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  • Node.js vs PHP processing speed

    - by Cody Craven
    I've been looking into node.js recently and wanted to see a true comparison of processing speed for PHP vs Node.js. In most of the comparisons I had seen, Node trounced Apache/PHP set ups handily. However all of the tests were small 'hello worlds' that would not accurately reflect any webpage's markup. So I decided to create a basic HTML page with 10,000 hello world paragraph elements. In these tests Node with Cluster was beaten to a pulp by PHP on Nginx utilizing PHP-FPM. So I'm curious if I am misusing Node somehow or if Node is really just this bad at processing power. Note that my results were equivalent outputting "Hello world\n" with text/plain as the HTML, but I only included the HTML as it's closer to the use case I was investigating. My testing box: Core i7-2600 Intel CPU (has 8 threads with 4 cores) 8GB DDR3 RAM Fedora 16 64bit Node.js v0.6.13 Nginx v1.0.13 PHP v5.3.10 (with PHP-FPM) My test scripts: Node.js script var cluster = require('cluster'); var http = require('http'); var numCPUs = require('os').cpus().length; if (cluster.isMaster) { // Fork workers. for (var i = 0; i < numCPUs; i++) { cluster.fork(); } cluster.on('death', function (worker) { console.log('worker ' + worker.pid + ' died'); }); } else { // Worker processes have an HTTP server. http.Server(function (req, res) { res.writeHead(200, {'Content-Type': 'text/html'}); res.write('<html>\n<head>\n<title>Speed test</title>\n</head>\n<body>\n'); for (var i = 0; i < 10000; i++) { res.write('<p>Hello world</p>\n'); } res.end('</body>\n</html>'); }).listen(80); } This script is adapted from Node.js' documentation at http://nodejs.org/docs/latest/api/cluster.html PHP script <?php echo "<html>\n<head>\n<title>Speed test</title>\n</head>\n<body>\n"; for ($i = 0; $i < 10000; $i++) { echo "<p>Hello world</p>\n"; } echo "</body>\n</html>"; My results Node.js $ ab -n 500 -c 20 http://speedtest.dev/ This is ApacheBench, Version 2.3 <$Revision: 655654 $> Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/ Licensed to The Apache Software Foundation, http://www.apache.org/ Benchmarking speedtest.dev (be patient) Completed 100 requests Completed 200 requests Completed 300 requests Completed 400 requests Completed 500 requests Finished 500 requests Server Software: Server Hostname: speedtest.dev Server Port: 80 Document Path: / Document Length: 190070 bytes Concurrency Level: 20 Time taken for tests: 14.603 seconds Complete requests: 500 Failed requests: 0 Write errors: 0 Total transferred: 95066500 bytes HTML transferred: 95035000 bytes Requests per second: 34.24 [#/sec] (mean) Time per request: 584.123 [ms] (mean) Time per request: 29.206 [ms] (mean, across all concurrent requests) Transfer rate: 6357.45 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 0 0 0.2 0 2 Processing: 94 547 405.4 424 2516 Waiting: 0 331 399.3 216 2284 Total: 95 547 405.4 424 2516 Percentage of the requests served within a certain time (ms) 50% 424 66% 607 75% 733 80% 813 90% 1084 95% 1325 98% 1843 99% 2062 100% 2516 (longest request) PHP/Nginx $ ab -n 500 -c 20 http://speedtest.dev/test.php This is ApacheBench, Version 2.3 <$Revision: 655654 $> Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/ Licensed to The Apache Software Foundation, http://www.apache.org/ Benchmarking speedtest.dev (be patient) Completed 100 requests Completed 200 requests Completed 300 requests Completed 400 requests Completed 500 requests Finished 500 requests Server Software: nginx/1.0.13 Server Hostname: speedtest.dev Server Port: 80 Document Path: /test.php Document Length: 190070 bytes Concurrency Level: 20 Time taken for tests: 0.130 seconds Complete requests: 500 Failed requests: 0 Write errors: 0 Total transferred: 95109000 bytes HTML transferred: 95035000 bytes Requests per second: 3849.11 [#/sec] (mean) Time per request: 5.196 [ms] (mean) Time per request: 0.260 [ms] (mean, across all concurrent requests) Transfer rate: 715010.65 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 0 0 0.2 0 1 Processing: 3 5 0.7 5 7 Waiting: 1 4 0.7 4 7 Total: 3 5 0.7 5 7 Percentage of the requests served within a certain time (ms) 50% 5 66% 5 75% 5 80% 6 90% 6 95% 6 98% 6 99% 6 100% 7 (longest request) Additional details Again what I'm looking for is to find out if I'm doing something wrong with Node.js or if it is really just that slow compared to PHP on Nginx with FPM. I certainly think Node has a real niche that it could fit well, however with these test results (which I really hope I made a mistake with - as I like the idea of Node) lead me to believe that it is a horrible choice for even a modest processing load when compared to PHP (let alone JVM or various other fast solutions). As a final note, I also tried running an Apache Bench test against node with $ ab -n 20 -c 20 http://speedtest.dev/ and consistently received a total test time of greater than 0.900 seconds.

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  • C++ long long manipulation

    - by Krakkos
    Given 2 32bit ints iMSB and iLSB int iMSB = 12345678; // Most Significant Bits of file size in Bytes int iLSB = 87654321; // Least Significant Bits of file size in Bytes the long long form would be... // Always positive so use 31 bts long long full_size = ((long long)iMSB << 31); full_size += (long long)(iLSB); Now.. I don't need that much precision (that exact number of bytes), so, how can I convert the file size to MiBytes to 3 decimal places and convert to a string... tried this... long double file_size_megs = file_size_bytes / (1024 * 1024); char strNumber[20]; sprintf(strNumber, "%ld", file_size_megs); ... but dosen't seem to work. i.e. 1234567899878Bytes = 1177375.698MiB ??

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  • May the FileInputStream.available foolish me?

    - by Tom Brito
    This FileInputStream.available() javadoc says: Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes. In some cases, a non-blocking read (or skip) may appear to be blocked when it is merely slow, for example when reading large files over slow networks. I'm not sure if in this check: if (new FileInputStream(xmlFile).available() == 0) can I rely that empty files will always return zero?

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  • Memory assignment of local variables

    - by Mask
    void function(int a, int b, int c) { char buffer1[5]; char buffer2[10]; } We must remember that memory can only be addressed in multiples of the word size. A word in our case is 4 bytes, or 32 bits. So our 5 byte buffer is really going to take 8 bytes (2 words) of memory, and our 10 byte buffer is going to take 12 bytes (3 words) of memory. That is why SP is being subtracted by 20. Why it's not ceil((5+10)/4)*4=16?

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  • Problem with MIB_IFTABLE & MIB_IFROW

    - by calvin
    Hello there, Im using MIB_IFTABLE & MIB_IFROW to get the no.of bytes transmitted & received. Everything looks fine, and values are correct in case of using WIFI alone. But when i use vpn connection over wifi these values are not correct for wifi adapter, interestingly i'm getting correct values for vpn adapter. And if i see status of any of these adapters(right click and see status), all these values given by windows are correct. here are my questions. 1) is there any other way of getting no.of bytes transferred over adapter? 2) is there a way to tell whether adapter is vpn or not? (as all vpn adapters are shows as Local Area Connection) 3) If you are connected to VPN, is there a possibility of bytes getting transferred through other than this vpn adapter?(forget about split tunneling, consider very simple case) i use vs2005, win7, Im new to these protocols, thanks for any help. -calvin

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  • How come string.maketrans does not work in Python 3.1?

    - by ShaChris23
    I'm a Python newbie. How come this doesn't work in Python 3.1? from string import maketrans # Required to call maketrans function. intab = "aeiou" outtab = "12345" trantab = maketrans(intab, outtab) str = "this is string example....wow!!!"; print str.translate(trantab); When I executed the above code, I get the following instead: Traceback (most recent call last): File "<pyshell#119>", line 1, in <module> transtab = maketrans(intab, outtab) File "/Library/Frameworks/Python.framework/Versions/3.1/lib/python3.1/string.py", line 60, in maketrans raise TypeError("maketrans arguments must be bytes objects") TypeError: maketrans arguments must be bytes objects What does "must be bytes objects" mean? Could anyone please help post a working code for Python 3.1 if it's possible?

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  • Reading a Windows 'binary' float into a ASP jscript variable

    - by user89691
    I need to read files produced by a legacy Windows app that stores real numbers (the 8-byte "double" type) in binary - i.e. as a packed array of 8 bytes. I can read the 8 byte group OK but how can I present it to my ASP JScript code such I can get the real number back again. Or to put it another way: Say a file was produced by a Windows (Delphi) program: Assign (f, 'test.bin') ; rewrite (f, 1) ; r := 1234.56E78 ; BlockWrite (f, r, SizeOf (Double)) ; Close (f) ; Inspection of the file will show it contains 8 bytes, being: 94 0E 4C CA C2 97 AD 53 which is the real number in IEEE format. Assuming I can read these 8 bytes back in ASP, is there a simple way of getting the real number back again?

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  • Find element with attribute with minidom

    - by Xster
    Given <field name="frame.time_delta_displayed" showname="Time delta from previous displayed frame: 0.000008000 seconds" size="0" pos="0" show="0.000008000"/> <field name="frame.time_relative" showname="Time since reference or first frame: 0.000008000 seconds" size="0" pos="0" show="0.000008000"/> <field name="frame.number" showname="Frame Number: 2" size="0" pos="0" show="2"/> <field name="frame.pkt_len" showname="Packet Length: 1506 bytes" hide="yes" size="0" pos="0" show="1506"/> <field name="frame.len" showname="Frame Length: 1506 bytes" size="0" pos="0" show="1506"/> <field name="frame.cap_len" showname="Capture Length: 1506 bytes" size="0" pos="0" show="1506"/> <field name="frame.marked" showname="Frame is marked: False" size="0" pos="0" show="0"/> <field name="frame.protocols" showname="Protocols in frame: eth:ip:tcp:http:data" size="0" pos="0" show="eth:ip:tcp:http:data"/> How do I get the field with name="frame.len" right away without iterating through every tag and checking the attributes?

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  • Create an assembly in memory

    - by Jared I
    I'd like to create an assembly in memory, using an using the classes in Reflection.Emit Currently, I can create the assembly and get it's bytes using something like AssemblyBuilder builder = AppDomain.CurrentDomain.DefineDynamicAssembly(..., AssemblyBuilderAccess.Save); ... create the assembly ... builder.Save(targetFileName); using(FileStream fs = File.Open(targetFileName, FileMode.Open)) { ... read the bytes from the file stream ... } However, it does so by creating a file on the local filesystem. I don't actually need the file, just the bytes that would be in the file. Is it possible to create the assembly without writing any files?

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  • understanding silverlight resource file format

    - by Quincy
    I'm trying to understand the format of silverlight resource files. There are 4 bytes of the data comes after PAD. I'd like to know what these values are, and how they are generated. here is the hex dump of a .g.resources file. Here is what I know: there is 0xbeefcace at the beginning, then there is dependancies, then padding. after that is the great unknown (but I really like to know). After 4 null bytes, are the file name and size of the resource. and After that is content of the said file. I'm not that familiar with .Net and silverlight resource management. would someone please tell me what the mystical 4 bytes are, or point me the url to the specification doc or something. Any help would be appreciated!

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  • Is there a simpler way to convert a byte array to a 2-byte-size hexadecimal string?

    - by Tom Brito
    Is there a simpler way of implement this? Or a implemented method in JDK or other lib? /** * Convert a byte array to 2-byte-size hexadecimal String. */ public static String to2DigitsHex(byte[] bytes) { String hexData = ""; for (int i = 0; i < bytes.length; i++) { int intV = bytes[i] & 0xFF; // positive int String hexV = Integer.toHexString(intV); if (hexV.length() < 2) { hexV = "0" + hexV; } hexData += hexV; } return hexData; } public static void main(String[] args) { System.out.println(to2DigitsHex(new byte[] {8, 10, 12})); } the output is: "08 0A 0C" (without the spaces)

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  • Programming a loopback-device consisting of several files in Linux

    - by dubbaluga
    Hej, it is relatively easy to use a file for emulating a block-device using losetup in Linux: http://www.walkernews.net/2007/07/01/create-linux-loopback-file-system-on-disk-file/ Can anyone please give me a hint on what to look for in case I want to program my own block-device which is based on several files I'm taking content from? For your understanding, I would like to let's say take bytes 1-500 and 1.000-3.000 from file1 and bytes 501-999 and bytes 3.001 to 5.000 from file2 to offer them as a combined block-device. My prefered programming language is Python and I want to write my program in user-space as much as possible. For Windows I found such an implementation. It's called FileDisk and HttpDisk and it can be found here: http://www.acc.umu.se/~bosse/ Thanks in advance and regards, Rainer

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  • What exactly does raw microphone data represent?

    - by esperantist
    I'm using PyAudio, a PortAudio wrapper for Python. I'm getting data from a microphone. Data which is represented by a continuous stream of bytes divided into chunks (of a size determined by me). I've tried to plot the signal, assuming the bytes represent the current signal amplitude, but I get an interesting image that I can't easily describe. ^^ It seems to be composed of two waves, one shifted from the other. What exactly do the particular bytes represent, and how does this change when I'm recording only one channel, instead of two? Any explanations, suggestions, code snippets, anything, very welcome! (I'm new at this.) Thanks!

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  • what causes the .NET SerialPort class DataReceived event to fire?

    - by Klay
    I understand from the MSDN docs that the event DataReceived will not necessarily fire once per byte. But does anyone know what exactly is the mechanism that causes the event to fire? Does the receipt of each byte restart a timer that has to reach, say 10 ms between bytes, before the event fires? I ask because I'm trying to write an app that reads XML data coming in from a serial port. Because my laptop has no serial ports, I use a virtual serial port emulator. (I know, I know--I can't do anything about it ATM). When I pass data through the emulated port to my app, the event fires once for each XML record (about 1500 bytes). Perfect. But when a colleague at another office tries it with two computers connected by an actual cable, the DataReceived event fires repeatedly, after every 10 or so bytes of XML, which totally throws off the app.

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  • How to generate a cryptographically secure Double between 0 and 1?

    - by Portman
    I know how to generate a random number between 0 and 1 using the NextDouble method of the pseudo-random number generator. var rng1 = new System.Random(); var random1 = rng1.NextDouble(); // generates a random double between 0 and 1.0 And I know how to fill a random byte array using the cryptographically secure random number generator. Byte[] bytes = new Byte[8]; var rng2 = new System.Security.Cryptography.RNGCryptoServiceProvider(); rng2.GetBytes(bytes); // generates 8 random bytes But how can I convert the byte-array output of RNGCryptoServiceProvider into a random number between 0 (inclusive) and 1 (exclusive)?

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  • How to read a file byte by byte in Python and how to print a bytelist as a binary?

    - by zaplec
    Hi, I'm trying to read a file byte by byte, but I'm not sure how to do that. I'm trying to do it like that: file = open(filename, 'rb') while 1: byte = file.read(8) # Do something... So does that make the variable byte to contain 8 next bits at the beginning of every loop? It doesn't matter what those bytes really are. The only thing that matters is that I need to read a file in 8-bit stacks. EDIT: Also I collect those bytes in a list and I would like to print them so that they don't print out as ASCII characters, but as raw bytes i.e. when I print that bytelist it gives the result as ['10010101', '00011100', .... ]

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  • PostGres - run a query in batches?

    - by CaffeineIV
    Is it possible to loop through a query so that if (for example) 500,000 rows are found, it'll return results for the first 10,000 and then rerun the query again? So, what I want to do is run a query and build an array, like this: $result = pg_query("SELECT * FROM myTable"); $i = 0; while($row = pg_fetch_array($result) ) { $myArray[$i]['id'] = $row['id']; $myArray[$i]['name'] = $row['name']; $i++; } But, I know that there will be several hundred thousand rows, so I wanted to do it in batches of like 10,000... 1- 9,999 and then 10,000 - 10,999 etc... The reason why is because I keep getting this error: Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 3 bytes) Which, incidentally, I don't understand how 3 bytes could exhaust 512M... So, if that's something that I can just change, that'd be great, although, still might be better to do this in batches?

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  • reading and writing QByteArrays

    - by synchronicity
    I'm having trouble reading and writing QByteArray data to a file. My goal is to save QPixmap data into a QByteArray and save that QByteArray to a file (with the ability to read this QByteArray back from the file and into a QPixmap). I want to use following code from the QPixmap documentation: QPixmap pixmap(<image path>); QByteArray bytes; QBuffer buffer(&bytes); buffer.open(QIODevice::WriteOnly); pixmap.save(&buffer, "PNG"); // writes pixmap into bytes in PNG format After writing the buffer to a file, I want to be able to retrieve the QByteArray and load it back into a QPixmap using the QPixmap::loadFromData() function. Please let me know if any further clarification is needed (I'm open to alternative approaches as well, I just need to be able to read and write the QPixmap to a file! :) );

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  • An MP3 parser to extract numbered frames?

    - by Xepoch
    I am writing a streaming application for MP3 (CBR). It is all passthru, meaning I don't have to decode/encode, I just need to pass on the data as I see it come through. I want to be able to count the MP3 frames as they passthru (and some other stuff like throughput calculations). According to the MP3 frame header spec, the sync word appears to be 11 bits of 1s, however I notice (naturally) that the frame payload which I should safely assume to be binary and thus it is not odd at all to see 11 1s in sequence. My questions: Is there a Unix/Linux MP3 parser utility (dd-style) that can pull numbered frames from an MP3 file/pipe? Any perl wisdom here? How does one delineate an MP3 header block from any other binary payload data? and lastly: Is a constant bitrate (CBR) MP3 defined by payload bytes or are the header bytes included in the aggregate # of bytes/bits per any given timeslice? Thanks,

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  • How do you calculate the storage size of a SimpleDB domain?

    - by C. Dragon 76
    The official documentation states: Raw byte size (GB) of all item IDs + 45 bytes per item + Raw byte size (GB) of all attribute names + 45 bytes per attribute name + Raw byte size (GB) of all attribute-value pairs + 45 bytes per attribute-value pair What is the raw size of an attribute-value pair? Is it precisely the size of the value? (I would expect so, but then why is it worded "attribute-value pair"?) Or is it the size of the attribute name plus the size of the attribute value? (In that case, there would be motivation to give your attributes really short names.) For example, what is the size of the tiny domain below? +---------------------------------------------------------+ | Item Name/ID | "Price" attribute | "Calories" attribute | |--------------+-------------------+----------------------| | "apple" | "0000.43" | "0046" | | "orange" | "0000.70" | "0053" | +---------------------------------------------------------+

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