**No**, you dont have to index it again. When you specify `UNIQUE KEY`, the column is indexed. So it has no difference in performance with other indexed column (e.g. PRIMARY KEY) of *same type*.

However if the type is different, there will be little performance difference.

Every `UNIQUE` field is by definition indexed with a `UNIQUE INDEX` - this also happens to be the fastest searchable access path.

If the field needs to be UNIQUE then it should either be the `PRIMARY KEY` or a `UNIQUE INDEX`.

As for performance between `UNIQUE INDEX` and `INDEX`, there is no difference when selecting as both will use the same algorithm i.e. hashing or b-tree.  It&#39;s just that with a `UNIQUE` index, especially a numeric i.e. `INT` one, it will be faster than an index which contains duplicates as algorithms such as b-tree are able to more efficiently get to the requested row(s)

I&#39;m having an error with Eclipse and Android&#39;s SDK. apparently, it comes from the fact that my certificate expired. So I googled the error and I found that I have to remove the ~/.android/debug.keystore file. The thing is I can&#39;t find this file. It&#39;s not in my SDK.

Can someone help me with this ?

Edit: I work on Mac.

I can&#39;t find the debug.keystore file

I have a `Func&lt;TCollection, T&gt;` in my code. I use it to select certain properties.

In a call to another method I need `Expression&lt;Func&lt;TCollection, T&gt;&gt;` as a parameter.

Is there any way to convert (or create from) `Func&lt;TCollection, T&gt;` to `Expression&lt;Func&lt;TCollection, T&gt;&gt;` ?

Thanx

Create Expression from Func

I have one `UNIQUE` field in my table, and I need to search over it quickly. Do I need to index it?

Do searches over unique fields and indexed fields vary in speed or resource usage?

MySQL: unique field needs to be an index?

<p>I have one <code>UNIQUE</code> field in my table, and I need to search over it quickly. Do I need to index it?</p>
<p>Do searches over unique fields and indexed fields vary in speed or resource usage?</p>


Only today I realized that I was missing this in my PHP scripts:

    mysql_set_charset(&#39;utf8&#39;);

All my tables are InnoDB, collation &quot;utf8_unicode_ci&quot;, and all my VARCHAR columns are &quot;utf8_unicode_ci&quot; as well. I have `mb_internal_encoding(&#39;UTF-8&#39;);` on my PHP scripts, and all my PHP files are encoded as UTF-8.

So, until now, every time I &quot;INSERT&quot; something with diacritics, example:

    mysql_query(&#39;INSERT INTO `table` SET `name`=&quot;J&#225;u&#242; I&#241;e&quot;&#39;);

The &#39;name&#39; contents would be, in this case: `J&#195;&#161;u&#195;&#178; I&#195;&#177;e`.  

Since I fixed the charset between PHP and MySQL, new INSERTs are now storing correctly. However, I want to fix all the older rows that are &quot;messed&quot; at the moment. I tried many things already, but it always breaks the strings on the first &quot;illegal&quot; character. Here is my current code:

    $m = mysql_real_escape_string(&#39;&#191;&lt;?php echo &quot;&#172;&lt;b&gt;\&#39;PHP &amp;aacute; (&#225;)ţări&#238;ş &lt;/b&gt;&quot;; ?&gt; ă-ţi abcdd;//;&#241;&#231;&#180;พดแทฝใจค&#231;ă&#226;ξβψδπλξξςαยน&#241; ;&#39;);
	mysql_set_charset(&#39;utf8&#39;);
	mysql_query(&#39;INSERT INTO `table` SET `name`=&quot;&#39;.$m.&#39;&quot;&#39;);
	mysql_set_charset(&#39;latin1&#39;);
	mysql_query(&#39;INSERT INTO `table` SET `name`=&quot;&#39;.$m.&#39;&quot;&#39;);
	mysql_set_charset(&#39;utf8&#39;);
	
	$result = mysql_iquery(&#39;SELECT * FROM `table`&#39;);
	while ($row = mysql_fetch_assoc($result)) {
		$message = $row[&#39;name&#39;];
		$message = mb_convert_encoding($message, &#39;ISO-8859-15&#39;, &#39;UTF-8&#39;);
		//$message = iconv(&quot;UTF-8&quot;, &quot;ISO-8859-1//IGNORE&quot;, $message);
		mysql_iquery(&#39;UPDATE `table` SET `name`=&quot;&#39;.mysql_real_escape_string($message).&#39;&quot; WHERE `a1`=&quot;&#39;.$row[&#39;a1&#39;].&#39;&quot;&#39;);
	}

It &quot;UPDATE&quot;s with the expected characters, except that the string gets truncated after the character &quot;ă&quot;. I mean, that character and following chars are not included on the string.

Also, testing with the &quot;iconv()&quot; (that is commented on the code) does the same, even with //IGNORE and //TRANSLIT

I also tested several charsets, between ISO-8859-1 and ISO-8859-15.

Convert latin1 characters on a UTF8 table into UTF8

MySQL How do you INSERT INTO a table with a SELECT subquery returning multiple rows?

  

      INSERT INTO Results
        (
         People,
         names,
        )
        VALUES
        (
         (
           SELECT d.id
           FROM Names f
           JOIN People d ON d.id  = f.id
         ),
        
         (
          &quot;Henry&quot;
         ),
        );

I **WANT** to populate the new table with all results returning from this subquery. How do I do this without getting a **ERROR 1242 (21000): Subquery returns more than 1 row**


MySQL How do you INSERT INTO a table with a SELECT subquery returning multiple rows?

I am using MySQL workbench - What is the difference between duration and fetch times when a query is run?

Also is there a way I can enable the microsecond option in MySQL?

mysql duration and fetch time

I have a MySQL dump of one of my databases. In it, there are DEFINER clauses which look like, 

    &quot;DEFINER=`root`@`localhost`&quot; 

Namely, these DEFINER clauses are on my CREATE VIEW and CREATE PROCEDURE statements. Is there a way to remove these DEFINER clauses from my dump file? 

Remove DEFINER clause from MySQL Dumps

I opened a ssh tunnel as described in this post: https://stackoverflow.com/questions/2807118/zend-db-how-to-connect-to-a-mysql-database-over-ssh-tunnel

But now I don&#39;t know what I actually did. Does this command affect anything on the server?
And how do I close this tunnel, because now I can&#39;t use my local mysql properly.

I use OSX Lion and the server runs on Ubuntu 11.10.

How to close this ssh tunnel?

I have a database with 3 columns: 
  
    id, name, somethingelse  
This table has no index set and i am getting &quot;No index defined!&quot; in phpmyadmin  
id is a 7digit alphanumeric value, unique to each row.  
I want to set Drugid to be the primarykey/index (i dont know the difference if there is one)  
Please explain in detail as i am new to this.  
Thank you.


SQL: set existing column as Primary Key in MySQL

A. How do I index `nested` and all of it&#39;s values?

B. How do I index `valuetwo`?

    {
        id: 00000,
        attrs: {
            nested:{
                value: value1,
                valuetwo: value2,
            }
        }
    }

I&#39;ve looked here: http://www.mongodb.org/display/DOCS/Indexes, and the docs to my knowledge, aren&#39;t clear about indexing things that aren&#39;t nested.

How to Create a nested index in MongoDB?

Should I **define a separate index** on the `email` column (for searching purposes), or is the index is &quot;automatically&quot; added along with `UNIQ_EMAIL_USER` constraint?

    CREATE TABLE IF NOT EXISTS `customer` (
      `id` int(11) NOT NULL AUTO_INCREMENT,
      `user_id` int(11) NOT NULL,
      `first` varchar(255) NOT NULL,
      `last` varchar(255) NOT NULL,
      `slug` varchar(255) NOT NULL,
      `email` varchar(255) NOT NULL,
      `created_at` datetime NOT NULL,
      `updated_at` datetime NOT NULL,
      PRIMARY KEY (`id`),
      UNIQUE KEY `UNIQ_SLUG` (`slug`),
      UNIQUE KEY `UNIQ_EMAIL_USER` (`email`,`user_id`),
      KEY `IDX_USER` (`user_id`)
    ) ENGINE=InnoDB;

**EDIT**: as suggested by Corbin i queried for `EXPLAIN SELECT * FROM customer WHERE email = &#39;address&#39;` on empty table. This is the result, i don&#39;t know how to interpret it:

    id select_type type possible_keys key  key_len ref  rows Extra
    1  SIMPLE      ALL  NULL	      NULL NULL    NULL 1    Using where

While adding an IXD_EMAIL to the table the same query shows:

    id select_type type possible_keys key       key_len ref   rows Extra
    1  SIMPLE      ref  IDX_EMAIL     IDX_EMAIL 257     const 1    Using where

Does a UNIQUE constraint automatically create an INDEX on the field(s)?

I have a `UNIQUE, NON CLUSTERED` index on a table that is currently using 4 columns for the index. 

I want to create an alter script that can merely add another column to this index. The new column type is `varchar`. 

The database is SQL Server 2005. 

Thanks in advance. 

SQL Server: how to write an alter index statement to add a column to the unique index?

To quote the [docs][1]:

&gt; When creating an index, the number associated with a key specifies the
&gt; direction of the index, so it should always be 1 (ascending) or -1
&gt; (descending). Direction doesn&#39;t matter for single key indexes or for
&gt; random access retrieval but is important if you are doing sorts or
&gt; range queries on compound indexes.

However, I see no reason why direction of the index should matter on compound indexes. Can someone please provide a further explanation (or an example)?

  [1]: http://www.mongodb.org/display/DOCS/Indexes

Why does direction of index matter in MongoDB?

In [C# in depth][1] (an excellent book thus far), Skeet explains *events aren&#39;t fields*. I read this section many times and I don&#39;t understand why the distinction makes any difference.

I am one of those developers that confuse events and delegate instances. In my mind, they are the same. Aren&#39;t both just a form of indirection? We can multicast both. An event is setup as a field as shorthand...sure. But, we are adding or removing handlers. Stacking them up to be called when the event fires. Don&#39;t we do the same thing with delegates, stack them up and call invoke?


  [1]: http://www.amazon.com/Depth-Second-Edition-Jon-Skeet/dp/1935182471

Events aren&#39;t fields - I don&#39;t get it

I created a class called _`Kwadrat`_. The class has three `int` fields. My _Development Environment_ suggests that I access the fields from _`Kwadrat`_ created objects via the __`::`__ &amp; __`-&gt;`__ operators. I tried both operators, and found that the __`-&gt;`__ operator is able to successfully access the data in the objects fields, although, the same cannot be said for the __`-&gt;`__ operator.
I have also found that the __`.`__ operator will access class members as well. I am confused, and don&#39;t understand why there are three members for accessing object members &amp;/or methods. Can someone please explain to me what the difference is between the three operators?

---

# &amp;nbsp; &amp;nbsp; &amp;nbsp; &amp;nbsp; &amp;nbsp; 1. `-&gt;`
# &amp;nbsp; &amp;nbsp; &amp;nbsp; &amp;nbsp; &amp;nbsp; 2. `::` 
# &amp;nbsp; &amp;nbsp; &amp;nbsp; &amp;nbsp; &amp;nbsp; 3. `.`

---

```C++


    #include &lt;iostream&gt;

    using namespace std;

    class Kwadrat{

    public: 
        int val1,
            val2,
            val3;

        Kwadrat(int val1, int val2, int val3)
        {
            this-&gt;val1 = val1; // Working
            this.val2 = val2;  // Doesn&#39;t Work!
            this::val3 = val3; // Doesn&#39;t Work!
        }
    };


    int main()
    {
        Kwadrat* kwadrat = new Kwadrat(1,2,3);

        cout&lt;&lt;kwadrat-&gt;val1&lt;&lt;endl;
        cout&lt;&lt;kwadrat-&gt;val2&lt;&lt;endl;
        cout&lt;&lt;kwadrat-&gt;val3&lt;&lt;endl;

        return 0;
    }


```


What is the difference between &quot;::&quot; &quot;.&quot; and &quot;-&gt;&quot; in c++

I wonder is there a way to get all private fields of some class in java and their type.

For example lets suppose I have a class

    class SomeClass {
        private String aaa;
        private SomeOtherClass bbb;
        private double ccc;
    }
Now I would like to get all private fields (`aaa`, `bbb`, `ccc`) of class `SomeClass` (Without knowing name of all fields upfront) and check their type.

Java reflection get all private fields

Is there a way to use javascript and JQuery to add some additional fields to be sent from a HTTP form using POST?

I mean:

    &lt;form action=&quot;somewhere&quot; method=&quot;POST&quot; id=&quot;form&quot;&gt;
      &lt;input type=&quot;submit&quot; name=&quot;submit&quot; value=&quot;Send&quot; /&gt;
    &lt;/form&gt;

    &lt;script type=&quot;text/javascript&quot;&gt;
      $(&quot;#form&quot;).submit( function(eventObj) {
        // I want to add a field &quot;field&quot; with value &quot;value&quot; here
        // to the POST data

        return true;
      });
    &lt;/script&gt;

How to add additional fields to form before submit?

If I specify *@AllArgsConstructor* using **Lombok**, it will generate a constructor for setting all the declared (not final, not static) fields. 
Is it possible to omit some field and this leave generated constructor for all other fields?



Java Lombok: Omitting one field in @AllArgsConstructor?

Let&#39;s take a simple &quot;Account Registration&quot; example, here is the flow:

- User visit website
- Click &quot;Register&quot; button and fill form, click &quot;Save&quot; button
- MVC Controller: Validate UserName uniqueness by reading from ReadModel 
- **RegisterCommand: Validate UserName uniqueness again (here is the question)**

Of course, we can validate UserName uniqueness by reading from ReadModel in MVC controller to improve performance and user experience. However, **we still need to validate the uniqueness again in RegisterCommand**, and obviously, we should NOT access ReadModel in Commands. 

If we do not use Event Sourcing, we can query the domain model, so that&#39;s no a problem. But if we&#39;re using Event Sourcing, we are not able to query domain model, so **how can we validate UserName uniqueness in RegisterCommand?** 

**Notice:** User class has an Id property, and UserName is not the key property of User class. We can only get the domain object by Id when using event sourcing.

**BTW:** In the requirement, if the entered UserName is already taken, the website should show error message &quot;Sorry, the user name XXX is not available&quot; to the visitor. It&#39;s not acceptable to show a message, say, &quot;We are creating your account, please wait, we will send the registration result to you via Email later&quot;, to the visitor.

Any ideas? Many thanks!

**[UPDATE]**

A more complex example:

**Requirement:**

When placing an order, the system should check the client&#39;s ordering history, if he is a valuable client (if the client placed at least 10 orders per month in the last year, he is valuable), we make 10% off to the order.

**Implementation:**

We create PlaceOrderCommand, and in the command, we need to query the ordering history to see if the client is valuable. But how can we do that? We shouldn&#39;t access ReadModel in command! As Mikael [said][1], we can use compensating commands in the account registration example, but if we also use that in this ordering example, it would be too complex, and the code might be too difficult to maintain.


  [1]: https://stackoverflow.com/a/9496198/290617

CQRS Event Sourcing: Validate UserName uniqueness

I have a dataframe with &gt;100 columns, and I would to find the unique rows by comparing only two of the columns. I&#39;m hoping this is an easy one, but I can&#39;t get it to work with `unique` or `duplicated` myself.

In the below, I would like to unique only using `id` and `id2`:

    data.frame(id=c(1,1,3),id2=c(1,1,4),somevalue=c(&quot;x&quot;,&quot;y&quot;,&quot;z&quot;))
  
    id id2 somevalue
    1   1         x
    1   1         y
    3   4         z

I would like to obtain either:

    id id2 somevalue
    1   1         x
    3   4         z

or:

    id id2 somevalue
    1   1         y
    3   4         z

(I have no preference which of the unique rows is kept)

Unique on a dataframe with only selected columns

Suppose I have an array

    a = np.array([1, 2, 1, 3, 3, 3, 0])

How can I (efficiently, Pythonically) find which elements of `a` are duplicates (i.e., non-unique values)?  In this case the result would be `array([1, 3, 3])` or possibly `array([1, 3])` if efficient.

I&#39;ve come up with a few methods that appear to work:

### Masking ###

    m = np.zeros_like(a, dtype=bool)
    m[np.unique(a, return_index=True)[1]] = True
    a[~m]

### Set operations ###

    a[~np.in1d(np.arange(len(a)), np.unique(a, return_index=True)[1], assume_unique=True)]

This one is cute but probably illegal (as `a` isn&#39;t actually unique):

    np.setxor1d(a, np.unique(a), assume_unique=True)

### Histograms ###

    u, i = np.unique(a, return_inverse=True)
    u[np.bincount(i) &gt; 1]

### Sorting ###

    s = np.sort(a, axis=None)
    s[:-1][s[1:] == s[:-1]]

### Pandas ###

    s = pd.Series(a)
    s[s.duplicated()]

Is there anything I&#39;ve missed?  I&#39;m not necessarily looking for a numpy-only solution, but it has to work with numpy data types and be efficient on medium-sized data sets (up to 10 million in size).

&lt;hr/&gt;

## Conclusions ##

Testing with a 10 million size data set (on a 2.8GHz Xeon):

    a = np.random.randint(10**7, size=10**7)

The fastest is sorting, at 1.1s.  The dubious `xor1d` is second at 2.6s, followed by masking and Pandas `Series.duplicated` at 3.1s, `bincount` at 5.6s, and `in1d` and senderle&#39;s `setdiff1d` both at 7.3s.  Steven&#39;s `Counter` is only a little slower, at 10.5s; trailing behind are Burhan&#39;s `Counter.most_common` at 110s and DSM&#39;s `Counter` subtraction at 360s.

I&#39;m going to use sorting for performance, but I&#39;m accepting Steven&#39;s answer because the performance is acceptable and it *feels* clearer and more Pythonic.

Edit: discovered the Pandas solution.  If Pandas is available it&#39;s clear and performs well.

Determining duplicate values in an array

I have a list of dates, each date in it can occur more than once. I want to count the number of times each date occurs (histogram) and display it in a graph (with the Y axis being the number of times the date occurs and the X axis being the date itself)?

Sample list:

    19/05/2012
    19/05/2012
    19/05/2012
    17/05/2012
    17/05/2012
    16/05/2012
    16/05/2012
    16/05/2012
    16/05/2012
    15/05/2012
    15/05/2012
    15/05/2012
    15/05/2012
    12/05/2012
    12/05/2012
    12/05/2012
    7/05/2012

I clicked every menu option over the past few years and never did I find anything specific to this. Would this be a case for using PivotTables somehow?

Count number of times a date occurs and make a graph out of it

Content Type	Original Author	Original Content on Stackoverflow
Question	TomSawyer	View Question on Stackoverflow
Solution 1 - Mysql	Shiplu Mokaddim	View Answer on Stackoverflow
Solution 2 - Mysql	Eugen Rieck	View Answer on Stackoverflow
Solution 3 - Mysql	Simon at My School Portal	View Answer on Stackoverflow

MySQL: unique field needs to be an index?

Mysql Problem Overview

Mysql Solutions

Solution 1 - Mysql

Solution 2 - Mysql

Solution 3 - Mysql

Create Expression from Func

I can't find the debug.keystore file

Attributions