To get current host name :-

    select @@hostname;
    show variables where Variable_name like &#39;%host%&#39;;

To get hosts for all incoming requests :-

    select host from information_schema.processlist;

Based on your last comment,  
I don&#39;t think you can resolve IP for the hostname using pure mysql function,  
as it require a network lookup, which could be taking long time. 

However, mysql document mention this :-

    resolveip google.com.sg

docs :- http://dev.mysql.com/doc/refman/5.0/en/resolveip.html

Maybe

    mysql&gt; show processlist;


I think you try to get the remote host of the conneting user...

You can get a String like &#39;myuser@localhost&#39; from the command:

    SELECT USER()

You can split this result on the &#39;@&#39; sign, to get the parts:


    -- delivers the &quot;remote_host&quot; e.g. &quot;localhost&quot; 
    SELECT SUBSTRING_INDEX(USER(), &#39;@&#39;, -1) 

    -- delivers the user-name e.g. &quot;myuser&quot;
    SELECT SUBSTRING_INDEX(USER(), &#39;@&#39;, 1)


if you are conneting via ip address you will get the ipadress instead of the hostname.

    show variables where Variable_name=&#39;hostname&#39;; 

That could help you !!

This can also be achieved by one single command. I tried these queries in MySQL 

to get hostname : 

    mysql&gt; SHOW GLOBAL VARIABLES LIKE &#39;HOSTNAME&#39;;
to get port : 

    mysql&gt; SHOW GLOBAL VARIABLES LIKE &#39;PORT&#39;;




I have a storyboard set up with working login and main view controller, the latter is the view controller to which the user is navigated to when login is successful.
My objective is to show the main view controller immediately if the authentication (stored in keychain) is successful, and show the login view controller if the authentication failed.
Basically, I want to do this in my AppDelegate:

    // url request &amp; response work fine, assume success is a BOOL here
    // that indicates whether login was successful or not

    if (success) {
              // &#39;push&#39; main view controller
    } else {
              // &#39;push&#39; login view controller
    }

I know about the method performSegueWithIdentifier: but this method is an instance method of UIViewController, so not callable from within AppDelegate.
How do I do this using my existing storyboard ??

EDIT:

The Storyboard&#39;s initial view controller now is a navigation controller which isn&#39;t connected to anything. I used the setRootViewController: distinction because MainIdentifier is a UITabBarController. Then this is what my lines look like:

    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    {        
        BOOL isLoggedIn = ...;    // got from server response
        
        NSString *segueId = isLoggedIn ? @&quot;MainIdentifier&quot; : @&quot;LoginIdentifier&quot;;
        UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@&quot;Storyboard&quot; bundle:nil];
        UIViewController *initViewController = [storyboard instantiateViewControllerWithIdentifier:segueId];
        
        if (isLoggedIn) {
            [self.window setRootViewController:initViewController];
        } else {
            [(UINavigationController *)self.window.rootViewController pushViewController:initViewController animated:NO];
        }
        
        return YES;
    }

Suggestions/improvements are welcome!

Conditionally start at different places in storyboard from AppDelegate

I use the Cobertura Maven plugin for one of my project. But I have a question about the generated report:

What is the difference between line and branch coverage?

Differences between Line and Branch coverage

    Show Database
    Use database
    show tables
    Describe &lt;table&gt;

All good and well, but is it possible to show the current connections host.
Not connection_id, but the IP Address or Name of the host.

Show MySQL host via SQL Command

<pre><code class="hljs language-sql">Show Database
Use database
show tables
Describe &#x3C;table>
</code></pre>
All good and well, but is it possible to show the current connections host.
Not connection_id, but the IP Address or Name of the host.

&gt; **Possible Duplicate:**  
&gt; [mysql datatype for telephne number and address](https://stackoverflow.com/questions/1846254/mysql-datatype-for-telephne-number-and-address)  

&lt;!-- End of automatically inserted text --&gt;

Any suggestions on best practice to store telephone numbers in a DB? Consider a US phone number:

 - 555 555 1212
 - 555-555-1212
 - (555) 555 1212
 - 5555551212
 - 1-555-555-1212
 - 1 (555) 555-1212
 - and so on ...

Should I remove formatting and store only numbers? Should I just use one field -- or split them up into: country code, area code, phone number, etc.? Suggestions?

How to store phone numbers on MySQL databases?

Every time is set up a new SQL table or add a new `varchar` column to an existing table, I am wondering one thing: what is the best value for the `length`. 

So, lets say, you have a column called `name` of type `varchar`. So, you have to choose the length. I cannot think of a name &gt; 20 chars, but you will never know. But instead of using 20, I always round up to the next 2^n number. In this case, I would choose 32 as the length. I do that, because from an computer scientist point of view, a number 2^n looks more `even` to me than other numbers and I&#39;m just assuming that the architecture underneath can handle those numbers slightly better than others.

On the other hand, MSSQL server for example, sets the default length value to 50, when you choose to create a varchar column. That makes me thinking about it. Why 50? is it just a random number, or based on average column length, or what?

It could also be - or probably is - that different SQL servers implementations (like MySQL, MSSQL, Postgres, ...) have different best column length values.



Best practices for SQL varchar column length

Is it possible to sort in mysql by &quot;order by&quot; using predefined set of column values (ID) like: order by (ID=1,5,4,3) so I would get record 1, 5, 4, 3 in that order out?

**UPDATE:** About abusing mysql ;-) I have to explain why I need this...

I want my records change sort randomly every 5 minutes. I have a cron task to do the update table to put different, random sort order in it. There is just one problem! PAGINATION. I will have a visitor who comes to my page and I give him first 20 results. He will wait 6 minutes and go to page 2 and he will have wrong results as the sort order had allready changed.

So I thought that if he comes to my site I put all the ID&#39;s to a session and when he is in page 2 he get&#39;s the correct records out even if the sorting allready changed.

Is there any other way, better, to do this?

Mysql order by specific ID values

I want to update a table in a statement that has several joins.  While I know the order of joins doesn&#39;t really matter (unless you you are using optimizer hints) I ordered them a certain way to be most intuitive to read.  However, this results in the table I want to update not being the one I start with, and I am having trouble updating it.  

A dummy example of what I&#39;d like to do is something like:

    UPDATE b
    FROM tableA a
    JOIN tableB b
       ON a.a_id = b.a_id
    JOIN tableC c
       ON b.b_id = c.b_id
    SET b.val = a.val+c.val
    WHERE a.val &gt; 10
        AND c.val &gt; 10;

There are many posts about updating with joins here however they always have table being updated first.  I know this is possible in SQL Server and hopefully its possible in MySQL Too!

MySQL update a joined table

In Linux, and many other systems, when navigating the terminal you can press &lt;kbd&gt;Tab&lt;/kbd&gt; to auto complete a directory or file name.

I&#39;m wondering if there is anything like that in the MySQL terminal. For example, if I want to get the description of `someTableWithRidiculousLongName` I could type `describe someTableW` then &lt;kbd&gt;Tab&lt;/kbd&gt; and it would auto-complete the rest.

Does anything like that exist in the MySQL terminal?


Autocompletion in the MySQL command-line client

I have a table with this layout:

    CREATE TABLE Favorites
    (
      FavoriteId uuid NOT NULL PRIMARY KEY,
      UserId uuid NOT NULL,
      RecipeId uuid NOT NULL,
      MenuId uuid
    )

I want to create a unique constraint similar to this:

    ALTER TABLE Favorites
    ADD CONSTRAINT Favorites_UniqueFavorite UNIQUE(UserId, MenuId, RecipeId);

However, this will allow multiple rows with the same `(UserId, RecipeId)`, if `MenuId IS NULL`.  I want to allow `NULL` in `MenuId` to store a favorite that has no associated menu, but I only want at most one of these rows per user/recipe pair.

The ideas I have so far are:

 1. Use some hard-coded UUID (such as all zeros) instead of null.  
However, `MenuId` has a FK constraint on each user&#39;s menus, so I&#39;d then have to create a special &quot;null&quot; menu for every user which is a hassle.

 2. Check for existence of a null entry using a trigger instead.  
I think this is a hassle and I like avoiding triggers wherever possible. Plus, I don&#39;t trust them to guarantee my data is never in a bad state.

 3. Just forget about it and check for the previous existence of a null entry in the middle-ware or in a insert function, and don&#39;t have this constraint.

I&#39;m using Postgres 9.0.

Is there any method I&#39;m overlooking?

Create unique constraint with null columns

I need to delete about 2 million rows from my PG database. I have a list of IDs that I need to delete. However, any way I try to do this is taking days.  

I tried putting them in a table and doing it in batches of 100. 4 days later, this is still running with only 297268 rows deleted. (I had to select 100 id&#39;s from an ID table, delete where IN that list, delete from ids table the 100 I selected).

I tried:

    DELETE FROM tbl WHERE id IN (select * from ids)

That&#39;s taking forever, too. Hard to gauge how long, since I can&#39;t see it&#39;s progress till done, but the query was still running after 2 days.

Just kind of looking for the most effective way to delete from a table when I know the specific ID&#39;s to delete, and there are millions of IDs.

Best way to delete millions of rows by ID

Division in sqlite return integer value

    sqlite&gt; select totalUsers/totalBids from 
    (select (select count(*) from Bids) as totalBids , 
    (select count(*) from Users) as totalUsers) A;
    1

Can we typecast the result to get the real value of division result?


converting int to real in sqlite

I have checked the documentation provided by Oracle and found a way to modify a constraint without dropping the table.  Problem is, it errors out at modify as it does not recognize the keyword.

Using EMS SQL Manager for PostgreSQL.

    Alter table public.public_insurer_credit MODIFY CONSTRAINT public_insurer_credit_fk1
        deferrable, initially deferred;

I was able to work around it by dropping the constraint using :


    ALTER TABLE &quot;public&quot;.&quot;public_insurer_credit&quot;
      DROP CONSTRAINT &quot;public_insurer_credit_fk1&quot; RESTRICT;
    
    ALTER TABLE &quot;public&quot;.&quot;public_insurer_credit&quot;
      ADD CONSTRAINT &quot;public_insurer_credit_fk1&quot; FOREIGN KEY (&quot;branch_id&quot;, &quot;order_id&quot;, &quot;public_insurer_id&quot;)
        REFERENCES &quot;public&quot;.&quot;order_public_insurer&quot;(&quot;branch_id&quot;, &quot;order_id&quot;, &quot;public_insurer_id&quot;)
        ON UPDATE CASCADE
        ON DELETE NO ACTION
        DEFERRABLE 
        INITIALLY DEFERRED;

Trying to modify a constraint in PostgreSQL

I have one problem with Android `SQLite` database.

I have one table which contains one field.StudentFname
and that application is working fine with Android 2.3.1 and now if I add another field then my application is not working properly. 

Can anyone help me who knows database very well,


How to add new Column to Android SQLite Database?

    ...
    user_id INTEGER NOT NULL, 
	CONSTRAINT fk_user_meta FOREIGN KEY (user_id)
		REFERENCES users (id) ON DELETE CASCADE ON UPDATE RESTRICT

I know from [here][1] that ON DELETE CASCADE means that if I delete a row from the users table, then the associated row from the user meta table will be removed too. But what does  ON UPDATE RESTRICT do?


  [1]: http://www.techonthenet.com/oracle/foreign_keys/foreign_delete.php

What does ON UPDATE RESTRICT do?

I have two tables and I need to create a view. The tables are:

    credit_orders(id, client_id, number_of_credits, payment_status)
    credit_usage(id, client_id, credits_used, date)

I use the following query to do this. The query without the &quot;create view&quot; part works well but with &quot;create view&quot;, it shows the error &quot;View&#39;s SELECT contains a subquery in the FROM clause&quot;. What could be the issue &amp; possible solution:

    create view view_credit_status as 
    (select credit_orders.client_id, 
            sum(credit_orders.number_of_credits) as purchased, 
            ifnull(t1.credits_used,0) as used 
     from credit_orders
     left outer join (select * from (select credit_usage.client_id, 
                                            sum(credits_used) as credits_used 
                                     from credit_usage 
                                     group by credit_usage.client_id) as t0
                      ) as t1 on t1.client_id = credit_orders.client_id
     where credit_orders.payment_status=&#39;Paid&#39;
     group by credit_orders.client_id)

View&#39;s SELECT contains a subquery in the FROM clause

I have read the quote :
*data depends on the key [1NF], the whole key [2NF] and nothing but the key [3NF]*. 

However, I am having trouble understanding 3.5NF or BCNF as it&#39;s called. Here is what I understand :

 - BCNF is stricter than 3NF
 - left side of any FD in the table must be a superkey (or at least a candidate key)

So why is it then, that some 3NF tables are not in BCNF? I mean, the 3NF quote explicitly says &quot;nothing but the key&quot; meaning that all attributes depend solely on the primary key. The primary key is, after all, a candidate key until it is chosen to be our primary key.

If anything is amiss regarding my understanding so far, please correct me and thanks for any help you can provide.




Difference between 3NF and BCNF in simple terms (must be able to explain to an 8-year old)

I have 3 types of users:

 - Admins
 - Suppliers
 - Employees

Each user type will have different user interface and access different types of data. Their only similarity is they are using one web application but they access totally different things. Is it better to put them all in one user table like tbl_users or is it better to create tbl_admins, tbl_suppliers, tbl_employees?

Content Type	Original Author	Original Content on Stackoverflow
Question	Craig Stewart	View Question on Stackoverflow
Solution 1 - Mysql	ajreal	View Answer on Stackoverflow
Solution 2 - Mysql	Adrian Cornish	View Answer on Stackoverflow
Solution 3 - Mysql	Radon8472	View Answer on Stackoverflow
Solution 4 - Mysql	Gowtham Vakani	View Answer on Stackoverflow
Solution 5 - Mysql	Vikas Bansal	View Answer on Stackoverflow

Show MySQL host via SQL Command

Mysql Problem Overview

Mysql Solutions

Solution 1 - Mysql

Solution 2 - Mysql

Solution 3 - Mysql

Solution 4 - Mysql

Solution 5 - Mysql

Differences between Line and Branch coverage

Conditionally start at different places in storyboard from AppDelegate

Attributions