It depends on the [collation][1] of the field - if it&#39;s `ci` (case insensitive) or `cs` (case sensitive). The unique index would apply accordingly.


  [1]: https://dev.mysql.com/doc/refman/8.0/en/charset.html

You can make a column case-sensitive by using this syntaxis.
the unique index also will be case-sensitive. 

&gt; ALTER  TABLE tbl_name MODIFY &lt;br&gt;
col_name column_definition &lt;br&gt;
[CHARACTER SET charset_name] &lt;br&gt;
[COLLATE collation_name]

Example:

&lt;!-- language: lang-sql --&gt;

    ALTER TABLE `tablename` MODIFY
    `column` VARCHAR(100) 
    CHARACTER SET utf8
    COLLATE utf8_bin;

**Note:** utf8_bin compares strings by the binary value of each character in the string.

Tested on Msql 5.5.X


I have a git directory which contains the a whole bunch of files and then has a directory called &#39;sessions&#39;. &#39;sessions&#39; contains cookie information for my web.py program. 

I need the folder &#39;sessions&#39; to remain in the git repository because without the folder the program does not function correctly. I don&#39;t need the actual contents of folder being stored in the git directory.

So the question is:

How can I get git to ignore the contents of a folder but not the folder itself?

How do you get git to ignore all contents of a directory?

I&#39;m currently building a MS Reporting Services Report that gets rendered to excel. I&#39;m trying to figure out how to set up the report so that it creates multiple Worksheets (Tabs) of the data on the report. I understand that entering a page break in the report gives you a new worksheet, however, is there a way to name each tab instead of it default to (worksheet 1, worksheet 2) etc.

Anyone know how this is done?

Thanks in advance!

Reporting Services export to Excel with Multiple Worksheets

Are indices *(indexes)* defined as UNIQUE case sensitive in MySQL?

Are UNIQUE indices case sensitive in MySQL?

<p>Are indices <em>(indexes)</em> defined as UNIQUE case sensitive in MySQL?</p>


I&#39;ve created a MySQL function and would like to raise an error if the values passed for the parameters are invalid. What are my options for raising an error within a MySQL function?

How to raise an error within a MySQL function

I&#39;d like to avoid mysqldump since that outputs in a form that is only convenient for mysql to read.  CSV seems more universal (one file per table is fine).  But if there are advantages to mysqldump, I&#39;m all ears.  Also, I&#39;d like something I can run from the command line (linux).  If that&#39;s a mysql script, pointers to how to make such a thing would be helpful.


Dump a mysql database to a plaintext (CSV) backup from the command line

I appreciate the semantic meaning of a NULL value in a database table, different from both false and the empty string &#39;&#39;.  However, I have often read about performance problems when fields are nullable and been advised to use an empty string in cases where NULL is actually semantically correct.  

What circumstances are appropriate to use nullable fields and NULL values?  What are the trade-offs?  Is it sensible to simply avoid using NULLs altogether and simply use empty strings, false or 0 to indicate the absence of a value?

**UPDATE**

OK - I understand the semantic difference between &#39;&#39; and NULL as well as the (performance-agnostic) circumstances in which NULL is the appropriate field value.  However, let me expand on the hinted performance issue.  This is from the excellent &quot;High Performance MySQL&quot; by Schwartz, Zeitsev et al 
[http://www.borders.co.uk/book/high-performance-mysql-optimization-backups-replication-and-more/857673/][1]:

&gt; It&#39;s harder for MySQL to optimize
&gt; queries that refer to nullable coumns,
&gt; because they make indexes, index
&gt; statistics, and value comparisons more
&gt; complicated.  A nullable column uses
&gt; more storage space and requires
&gt; special processing inside MySQL.  When
&gt; a nullable column is indexed, it
&gt; requires an extra byte per entry and
&gt; can even cause a fixed-size inded
&gt; (such as an index on a single integer
&gt; column) to be converted to a
&gt; variable-sized one in MyISAM.

More here:
[Google books preview][2]

This is quite possibly the definitive answer - I was just looking for second opinions and experience from the front-line.


  [1]: http://www.borders.co.uk/book/high-performance-mysql-optimization-backups-replication-and-more/857673/
  [2]: http://books.google.com/books?id=BL0NNoFPuAQC&amp;pg=PA81&amp;lpg=PA81&amp;dq=%22avoid+null+if+possible%22&amp;source=web&amp;ots=CNSMtvsC4R&amp;sig=Bbp2iSaTdzWpgYhOOcat3aKLuzI&amp;hl=en&amp;sa=X&amp;oi=book_result&amp;resnum=3&amp;ct=result

When to use NULL in MySQL tables

I have to create a report on some student completions. The students each belong to one client. Here are the tables (simplified for this question).

    CREATE TABLE  `clients` (
      `clientId` int(10) unsigned NOT NULL auto_increment,
      `clientName` varchar(100) NOT NULL default &#39;&#39;,
      `courseNames` varchar(255) NOT NULL default &#39;&#39;
    )

The `courseNames` field holds a comma-delimited string of course names, eg &quot;AB01,AB02,AB03&quot;

    CREATE TABLE  `clientenrols` (
      `clientEnrolId` int(10) unsigned NOT NULL auto_increment,
      `studentId` int(10) unsigned NOT NULL default &#39;0&#39;,
      `courseId` tinyint(3) unsigned NOT NULL default &#39;0&#39;
    )

The `courseId` field here is **the index of the course name in the clients.courseNames field**. So, if the client&#39;s `courseNames` are &quot;AB01,AB02,AB03&quot;, and the `courseId` of the enrolment is `2`, then the student is in AB03.

Is there a way that I can do a single select on these tables that includes the course name? Keep in mind that there will be students from different clients (and hence have different course names, not all of which are sequential,eg: &quot;NW01,NW03&quot;)

Basically, if I could split that field and return a single element from the resulting array, that would be what I&#39;m looking for. Here&#39;s what I mean in magical pseudocode:

    SELECT e.`studentId`, SPLIT(&quot;,&quot;, c.`courseNames`)[e.`courseId`]
    FROM ...



Can you split/explode a field in a MySQL query?

I wonder is there any positive effect in using UNSIGNED flag on defining some integer field in MySQL? Does it make queries faster or database smaller? Or should I only bother with it if I&#39;m concerned about upper limit?

Signed or unsigned in MySQL

Suppose I have 2 tables, Products and ProductCategories. Both tables have relationship on CategoryId. And this is the query.

    SELECT p.ProductId, p.Name, c.CategoryId, c.Name AS Category
    FROM Products p
    INNER JOIN ProductCategories c ON p.CategoryId = c.CategoryId
    WHERE c.CategoryId = 1;

When I create execution plan, table ProductCategories performs cluster index seek, which is as expectation. But for table Products, it performs cluster index scan, which make me doubt. Why FK does not help improve query performance?

So I have to create index on Products.CategoryId. When I create execution plan again, both tables perform index seek. And estimated subtree cost is reduced a lot.

My questions are:

1. Beside FK helps on relationship constraint, does it have any other usefulness? Does it improve query performance?

2. Should I create index on all FK columns (liked Products.CategoryId) in all tables?

Does Foreign Key improve query performance?

I have the following array, which I would like to reindex so the keys are reversed (ideally starting at 1):

Current array (**edit:** the array actually looks like this):

    Array (
    
    [2] =&gt; Object
        (
            [title] =&gt; Section
            [linked] =&gt; 1
        )

    [1] =&gt; Object
        (
            [title] =&gt; Sub-Section
            [linked] =&gt; 1
        )

    [0] =&gt; Object
        (
            [title] =&gt; Sub-Sub-Section
            [linked] =&gt; 
        )

    )

How it should be:

    Array (

    [1] =&gt; Object
        (
            [title] =&gt; Section
            [linked] =&gt; 1
        )

    [2] =&gt; Object
        (
            [title] =&gt; Sub-Section
            [linked] =&gt; 1
        )

    [3] =&gt; Object
        (
            [title] =&gt; Sub-Sub-Section
            [linked] =&gt; 
        )

    )


How do you reindex an array in PHP but with indexes starting from 1?

Can you explain the concepts of, and relationship between, Covering Indexes and Covered Queries in Microsoft&#39;s SQL Server?

What are Covering Indexes and Covered Queries in SQL Server?

How do I remove an element from a list **by index**?

I found `list.remove()`, but this slowly scans the list for an item **by value**.



How to remove an element from a list by index

I have a list and I want to remove a single element from it.  How can I do this?

I&#39;ve tried looking up what I think the obvious names for this function would be in the reference manual and I haven&#39;t found anything appropriate.

How can I remove an element from a list?

I am generating associative arrays and the key value is a string concat of 1..n columns.

Is there a max length for keys that will come back to bite me? If so, I&#39;ll probably stop and do it differently.

What is the max key size for an array in PHP?

Regarding the C++ STL map, erasing by key:-

     size_type map::erase ( const key_type&amp; x );

Is it legal to erase a non-existing key? i.e. is the snippet below ok?

    map&lt;char,int&gt; mymap;
    mymap[&#39;c&#39;]=30;
    mymap.erase(&#39;c&#39;);
    mymap.erase(&#39;c&#39;);
    mymap.erase(&#39;D&#39;);

Cheers


C++ STL map::erase a non-existing key

What are the differences between PRIMARY, UNIQUE, INDEX and FULLTEXT when creating MySQL tables?

How would I use them?

Differences between INDEX, PRIMARY, UNIQUE, FULLTEXT in MySQL?

I have a Perl script that is counting the number of occurrences of various strings in a text file. I want to be able to check if a certain string is not yet a key in the hash. Is there a better way of doing this altogether?

Here is what I am doing:

    foreach $line (@lines){
        if(($line =~ m|my regex|) )
        {
            $string = $1;
            if ($string is not a key in %strings) # &quot;strings&quot; is an associative array
            {
                $strings{$string} = 1;
            }
            else
            {
                $n = ($strings{$string});
                $strings{$string} = $n +1;
            }
        }
    }


How can I see if a Perl hash already has a certain key?

Do you need to explicitly create an index, or is it implicit when defining the primary key?  Is the answer the same for MyISAM and InnoDB?

Is the primary key automatically indexed in MySQL?

Given a list of strings, I want to sort it alphabetically and remove duplicates. I know I can do this:

    from sets import Set
    [...]
    myHash = Set(myList)

but I don&#39;t know how to retrieve the list members from the hash in alphabetical order.

I&#39;m not married to the hash, so any way to accomplish this will work. Also, performance is not an issue, so I&#39;d prefer a solution that is expressed in code clearly to a fast but more opaque one.


How to sort and remove duplicates from Python list?

Is there a built-in that removes duplicates from list in Python, whilst preserving order? I know that I can use a set to remove duplicates, but that destroys the original order. I also know that I can roll my own like this:

    def uniq(input):
      output = []
      for x in input:
        if x not in output:
          output.append(x)
      return output

(Thanks to [unwind][1] for that [code sample][2].)

But I&#39;d like to avail myself of a built-in or a more Pythonic idiom if possible.

Related question: [In Python, what is the fastest algorithm for removing duplicates from a list so that all elements are unique *while preserving order*?][3]


  [1]: https://stackoverflow.com/users/28169/unwind
  [2]: https://stackoverflow.com/questions/479897/how-do-you-remove-duplicates-from-a-list-in-python#479921
  [3]: https://stackoverflow.com/questions/89178/in-python-what-is-the-fastest-algorithm-for-removing-duplicates-from-a-list-so-t

How do you remove duplicates from a list whilst preserving order?

I have a ksh script that returns a long list of values, newline separated, and I want to see only the unique/distinct values. It is possible to do this?

For example, say my output is file suffixes in a directory:

&gt;     tar
&gt;     gz
&gt;     java
&gt;     gz
&gt;     java
&gt;     tar
&gt;     class
&gt;     class

I want to see a list like:

&gt;     tar
&gt;     gz
&gt;     java
&gt;     class



Select unique or distinct values from a list in UNIX shell script

Is there a way of getting a unique identifier of an instance?

`GetHashCode()` is the same for the two references pointing to the same instance. However, two different instances can (quite easily) get the same hash code:

    Hashtable hashCodesSeen = new Hashtable();
    LinkedList&lt;object&gt; l = new LinkedList&lt;object&gt;();
    int n = 0;
    while (true)
    {
        object o = new object();
        // Remember objects so that they don&#39;t get collected.
        // This does not make any difference though :(
        l.AddFirst(o);
        int hashCode = o.GetHashCode();
        n++;
        if (hashCodesSeen.ContainsKey(hashCode))
        {
            // Same hashCode seen twice for DIFFERENT objects (n is as low as 5322).
            Console.WriteLine(&quot;Hashcode seen twice: &quot; + n + &quot; (&quot; + hashCode + &quot;)&quot;);
            break;
        }
        hashCodesSeen.Add(hashCode, null);
    }

I&#39;m writing a debugging addin, and I need to get some kind of ID for a reference which is unique during the run of the program.

I already managed to get internal ADDRESS of the instance, which is unique until the garbage collector (GC) compacts the heap (= moves the objects = changes the addresses).

Stack&amp;nbsp;Overflow question *[Default implementation for Object.GetHashCode()][5]* might be related.

The objects are not under my control as I am accessing objects in a program being debugged using the debugger API. If I was in control of the objects, adding my own unique identifiers would be trivial.

I wanted the unique ID for building a hashtable ID -&gt; object, to be able to lookup already seen objects. For now I solved it like this:

    Build a hashtable: &#39;hashCode&#39; -&gt; (list of objects with hash code == &#39;hashCode&#39;)
    Find if object seen(o) {
        candidates = hashtable[o.GetHashCode()] // Objects with the same hashCode.
        If no candidates, the object is new
        If some candidates, compare their addresses to o.Address
            If no address is equal (the hash code was just a coincidence) -&gt; o is new
            If some address equal, o already seen
    }

   [5]: https://stackoverflow.com/questions/720177/default-implementation-for-object-gethashcode


.NET unique object identifier

I would like to create a method which takes either a filename as a `string` or a `FileInfo` and adds an incremented number to the filename if the file exists. But can&#39;t quite wrap my head around how to do this in a good way.

For example, if I have this FileInfo

    var file = new FileInfo(@&quot;C:\file.ext&quot;);

I would like the method to give me a new FileInfo with *C:\file 1.ext* if *C:\file.ext*
existed, and *C:\file 2.ext* if *C:\file 1.ext* existed and so on. Something like this:

    public FileInfo MakeUnique(FileInfo fileInfo)
    {
        if(fileInfo == null)
            throw new ArgumentNullException(&quot;fileInfo&quot;);
        if(!fileInfo.Exists)
            return fileInfo;

        // Somehow construct new filename from the one we have, test it, 
        // then do it again if necessary.
    }



C#: How would you make a unique filename by adding a number?

In Python, I can compile a regular expression to be case-insensitive using `re.compile`:

    &gt;&gt;&gt; s = &#39;TeSt&#39;
    &gt;&gt;&gt; casesensitive = re.compile(&#39;test&#39;)
    &gt;&gt;&gt; ignorecase = re.compile(&#39;test&#39;, re.IGNORECASE)
    &gt;&gt;&gt; 
    &gt;&gt;&gt; print casesensitive.match(s)
    None
    &gt;&gt;&gt; print ignorecase.match(s)
    &lt;_sre.SRE_Match object at 0x02F0B608&gt;

Is there a way to do the same, but without using `re.compile`. I can&#39;t find anything like Perl&#39;s `i` suffix (e.g. `m/test/i`) in the documentation.

Case insensitive regular expression without re.compile?

Are there any *formal* recommendations on element casing in XML?

I know XHTML uses lowercase element names (as opposed to HTML which canonically uses uppercase but is case-insensitive.)

But I&#39;m talking about XML for generic content.

## lowercase: ##

    &lt;customer&gt; 
       &lt;accountnumber&gt;619&lt;/accountnumber&gt;
       &lt;name&gt;Shelby Lake&lt;/name&gt;
    &lt;/customer&gt;

## camelCase: ##
    &lt;customer&gt; 
       &lt;accountNumber&gt;619&lt;/accountNumber&gt;
       &lt;name&gt;Shelby Lake&lt;/name&gt;
    &lt;/customer&gt;

## PascalCase: ##
    &lt;Customer&gt; 
       &lt;AccountNumber&gt;619&lt;/AccountNumber&gt;
       &lt;Name&gt;Shelby Lake&lt;/Name&gt;
    &lt;/Customer&gt;

## UPPERCASE: ##
    &lt;CUSTOMER&gt; 
       &lt;ACCOUNTNUMBER&gt;619&lt;/ACCOUNTNUMBER&gt;
       &lt;NAME&gt;Shelby Lake&lt;/NAME&gt;
    &lt;/CUSTOMER&gt;

**Note:** I&#39;m looking for cited guidelines rather than opinions. But the opinion with the most up-votes can be considered a guideline.

Case conventions on element names?

Is the indexOf(String) method case sensitive?  If so, is there a case insensitive version of it?

indexOf Case Sensitive?

How can I check to see if a database in SQL Server is case-sensitive? I have previously been running the query:

    SELECT CASE WHEN &#39;A&#39; = &#39;a&#39; THEN &#39;NOT CASE SENSITIVE&#39; ELSE &#39;CASE SENSITIVE&#39; END

But I am looking for other ways as this has actually given me issues in the past.

Edit - A little more info:
An existing product has many pre-written stored procedures. In a stored procedure `@test != @TEST` depending on the sensitivity of the server itself. So what I&#39;m looking for is the best way to check the server for its sensitivity.

SQL Server check case-sensitivity?

If I have a column names called `category_id` and `Category_Id`, are they different?

And if I have table called `category` and `Category`, are they different?

 

Content Type	Original Author	Original Content on Stackoverflow
Question	nickf	View Question on Stackoverflow
Solution 1 - Mysql	Eran Galperin	View Answer on Stackoverflow
Solution 2 - Mysql	Hemerson Varela	View Answer on Stackoverflow

Are UNIQUE indices case sensitive in MySQL?

Mysql Problem Overview

Mysql Solutions

Solution 1 - Mysql

Solution 2 - Mysql

Reporting Services export to Excel with Multiple Worksheets

How do you get git to ignore all contents of a directory?

Attributions