You might want to specify the protocol (like &#39;`tcp`&#39;), instead of `localhost` directly.  
See [those examples][1]:

    user:password@tcp(localhost:5555)/dbname

In your case:

    username@tcp(localhost)/my_db

----


Note, if you use the default protocol (`tcp`) and host (`localhost:3306`), this could be rewritten as

    user:password@/dbname


  [1]: https://github.com/go-sql-driver/mysql#examples

I had the same problem and the most voted answer couldn&#39;t help me. What saved me was putting `(host:port)` inside quotation --&gt; `&quot;(host:port)&quot;`

I had faced a similar issue as I was running Docker containers on my Linux VM. In my application (`server.go`) I changed the localhost value to use the IP of my virtual machine and then build and ran the container successfully.
```
mysql container (3307) &lt;--&gt; [(application mysql:&lt;vm ip&gt;:3307) container](expose 3000) &lt;--&gt;  world 
```

What does this annotation do?   
 When would I want to use it?   
  When would I not want to use it?

    @RunWith(SpringJUnit4ClassRunner.class)

I can find more usages of this when I Google and do not find a 101 explanation as to what this annotation is supposed to communicate to me or when/why I would use it?

What does this do: @RunWith(SpringJUnit4ClassRunner.class)

I am trying to set the width of columns in a DataTable rendered in Shiny and am not able to implement it using the aoColumnDefs options. Has anyone tried this before ? My table has 1 text followed by 3 numeric columns. The numeric columns need to be narrower and the 1st column (text) wider.

    output$result &lt;- renderDataTable({
	z &lt;- as(dataInput(), &quot;data.frame&quot;)
	setnames(z, c(&quot;Rules&quot;, &quot;Support&quot;, &quot;Confidence&quot;, &quot;StatDep&quot;))
    z
    }, options = list(aLengthMenu = c(5, 30, 50), iDisplayLength = 5, bSortClasses = TRUE,
                  aoColumnDefs = list(sWidth = &quot;50px&quot;, aTargets = list(1))))

Thanks,

- Raj.

** Update ** This seems to be working, but there might be other options to do this as well.

    output$result &lt;- renderDataTable({
	z &lt;- as(dataInput(), &quot;data.frame&quot;)
	setnames(z, c(&quot;Rules&quot;, &quot;Support&quot;, &quot;Confidence&quot;, &quot;StatDep&quot;))
    z
    }, options = list(aLengthMenu = c(5, 30, 50), iDisplayLength = 5, bSortClasses = TRUE,
                  bAutoWidth = FALSE,
                  aoColumn = list(list(sWidth = &quot;150px&quot;, sWidth = &quot;30px&quot;,
                                           sWidth = &quot;30px&quot;, sWidth = &quot;30px&quot;))
                                      ))


R Shiny set DataTable column width

I&#39;m trying to follow the instructions here https://github.com/go-sql-driver/mysql#installation and http://go-database-sql.org/accessing.html to create a sql.db.

The first line of my code has this

    db, err := sql.Open(&quot;mysql&quot;, &quot;username@localhost/my_db&quot;)

When I ran the program on the terminal, I got this:

    Default addr for network &#39;&#39;localhost&#39;&#39; unknown

Why is this? When I checked the user and host to mysql it states &#39;username&#39; and &#39;localhost&#39;. I followed the parameters like this:

    [username[:password]@][protocol[(address)]]/dbname[?param1=value1&amp;...&amp;paramN=valueN]

error connecting to database with mysqldriver

I'm trying to follow the instructions here <a href="https://github.com/go-sql-driver/mysql#installation" target="_blank" rel="noopener noreferrer">https://github.com/go-sql-driver/mysql#installation</a> and <a href="http://go-database-sql.org/accessing.html" target="_blank" rel="noopener noreferrer">http://go-database-sql.org/accessing.html</a> to create a sql.db.
The first line of my code has this
<pre><code class="hljs language-css">db, err := sql.Open("mysql", "username@localhost/my_db")
</code></pre>
When I ran the program on the terminal, I got this:
<pre><code class="hljs language-sql">Default addr for network ''localhost'' unknown
</code></pre>
Why is this? When I checked the user and host to mysql it states 'username' and 'localhost'. I followed the parameters like this:
<pre><code class="hljs language-ini">[username[:password]@][protocol[(address)]]/dbname[?param1=value1&#x26;...&#x26;paramN=valueN]
</code></pre>

When we create a table in MySQL with a `VARCHAR` column, we have to set the length for it. But for `TEXT` type we don&#39;t have to provide the length. 

What are the differences between `VARCHAR` and `TEXT`?

Difference between VARCHAR and TEXT in MySQL

I&#39;ve read a lot of questions about that but i couldn&#39;t find one that is fast enough. I think there are better ways to insert a lot of rows into a MySQL Database

 
I use the following code to insert 100k into my MySQL-Database:

    public static void CSVToMySQL()
    {
        string ConnectionString = &quot;server=192.168.1xxx&quot;;
        string Command = &quot;INSERT INTO User (FirstName, LastName ) VALUES (@FirstName, @LastName);&quot;;
        using (MySqlConnection mConnection = new MySqlConnection(ConnectionString))
        {
            mConnection.Open();

            for(int i =0;i&lt; 100000;i++) //inserting 100k items
            using (MySqlCommand myCmd = new MySqlCommand(Command, mConnection))
            {
                myCmd.CommandType = CommandType.Text;
                myCmd.Parameters.AddWithValue(&quot;@FirstName&quot;, &quot;test&quot;);
                myCmd.Parameters.AddWithValue(&quot;@LastName&quot;, &quot;test&quot;);
                myCmd.ExecuteNonQuery();
            }
        }
    }


This takes for 100k rows about 40 seconds. How can i make this faster or a little more efficient? 

Might be faster to insert multiple rows via a DataTable/DataAdapter or at once:

    INSERT INTO User (Fn, Ln) VALUES (@Fn1, @Ln1), (@Fn2, @Ln2)...

Due to security issues i can&#39;t load the data into a file and MySQLBulkLoad it.

Most efficient way to insert Rows into MySQL Database

So I have read the following post&quot;

[What the difference between mysql and mysql2 gem][1]

So far I have only used MongoDB with NodeJS and I want to be able to learn MySQL for any of my relational database needs. While researching MySQL &amp; NodeJS I have found repositories for MySQL2 and it appears to have nothing in relation to the MySQL website, I&#39;m assuming that there have been API&#39;s created that make it faster for developing with languages like NodeJS &amp; Ruby. From a NodeJS standpoint, I&#39;m assuming that I still run the regular MySQL database o my server, but I need to interact with it using these new API&#39;s like:

https://github.com/sidorares/node-mysql2/blob/master/README.md

I have also seen a site where they do performance benchmarks and NodeJS &amp; MySQL come in very low for performance. and NodeJS &amp; MySQL2 very High

Source for this info:
[php-nodejs-mysql-and-mongo][2]

Image  from this post:

![enter image description here][3]

Question: Do I simply use the regular MySQL database on my server and use this mysql2 API or is there a different implementation of MySQL that works with this API?

I have not used MySQL in about 10 years. I have only Used Microsoft&#39;s SQL Server. So I&#39;m severely behind. I have started using NodeJS and figured that my best relational database options were MySQL, Is there something else I should look for?

  [1]: https://stackoverflow.com/questions/5411551/what-the-difference-between-mysql-and-mysql2-gem
  [2]: http://zzarbi.tumblr.com/post/16870870471/php-nodejs-mysql-and-mongo
  [3]: http://i.stack.imgur.com/6BkJB.png

What is the difference between MySQL &amp; MySQL2 considering NodeJS

First off, yeah, I&#39;ve already seen this: 

[pip install mysql-python fails with EnvironmentError: mysql_config not found][1]

**The problem**

I am trying to use Django on a Google App Engine project. However, I haven&#39;t been able to get started as the server fails to start properly due to: 

    ImproperlyConfigured(&quot;Error loading MySQLdb module: %s&quot; % e)
    ImproperlyConfigured: Error loading MySQLdb module: No module named MySQLdb

I did some research and it all pointed to having to install Mysql-python, as apparently it isn&#39;t on my system. I actually tried uninstalling it and got this: 

    Cannot uninstall requirement mysql-python, not installed

Whenever I actually do try to install via: 

    sudo pip install MySQL-python

I get an error stating: 

    raise EnvironmentError(&quot;%s not found&quot; % (mysql_config.path,))
    EnvironmentError: mysql_config not found

I&#39;ve already tried running: 

    export PATH=$PATH:/usr/local/mysql/bin

but that didn&#39;t seem to help, as I ran the installation command again and it still failed. 

Any ideas? 

Please note I&#39;m not in a virtualenv. 

  [1]: https://stackoverflow.com/questions/5178292/pip-install-mysql-python-fails-with-environmenterror-mysql-config-not-found

Mac OS X - EnvironmentError: mysql_config not found

I am deploying a few different docker containers, mysql being the first one. I want to run scripts as soon as database is up and proceed to building other containers. The script has been failing because it was trying to run when the entrypoint script, which sets up mysql (from [this official mysql container](https://registry.hub.docker.com/_/mysql/)), was still running.

    sudo docker run --name mysql -e MYSQL_ROOT_PASSWORD=MY_ROOT_PASS -p 3306:3306 -d mysql
    [..] wait for mysql to be ready [..]
    mysql -h 127.0.0.1 -P 3306 -u root --password=MY_ROOT_PASS &lt; MY_SQL_SCRIPT.sql


Is there a way to wait for a signal of an entrypoiny mysql setup script finishing inside the docker container? Bash sleep seems like a suboptimal solution.

EDIT: Went for a bash script like this. Not the most elegant and kinda brute force but works like a charm. Maybe someone will find that useful.


    OUTPUT=&quot;Can&#39;t connect&quot;
    while [[ $OUTPUT == *&quot;Can&#39;t connect&quot;* ]]
    do
    	OUTPUT=$(mysql -h $APP_IP -P :$APP_PORT -u yyy --password=xxx &lt;       ./my_script.sql 2&gt;&amp;1)
    done



How do I know when my docker mysql container is up and mysql is ready for taking queries?

I see lots of tutorials and examples on how to make Go wait for x number of goroutines to finish, but what I&#39;m trying to do is have ensure there are always x number running, so a new goroutine is launched as soon as one ends.

Specifically I have a few hundred thousand &#39;things to do&#39; which is processing some stuff that is coming out of MySQL. So it works like this:

    db, err := sql.Open(&quot;mysql&quot;, connection_string)
    checkErr(err)
    defer db.Close()
    
    rows,err := db.Query(`SELECT id FROM table`)
    checkErr(err)
    defer rows.Close()
    
    var id uint
    for rows.Next() {
    	err := rows.Scan(&amp;id)
    	checkErr(err)
    	go processTheThing(id)
    	}
    checkErr(err)
    rows.Close()

Currently that will launch several hundred thousand threads of `processTheThing()`. What I need is that a maximum of x number (we&#39;ll call it 20) goroutines are launched. So it starts by launching 20 for the first 20 rows, and from then on it will launch a new goroutine for the next id the moment that one of the current goroutines has finished. So at any point in time there are always 20 running.

I&#39;m sure this is quite simple/standard, but I can&#39;t seem to find a good explanation on any of the tutorials or examples or how this is done.

Always have x number of goroutines running at any time

Can someone explain to me why appending to an array works when you do this:

    func (s *Sample) Append(name string) {
    	d := &amp;Stuff{
    		name: name,
    	}
    	s.data = append(s.data, d)
    }

[Full code here](http://play.golang.org/p/QCNEJG1nC9)

But not when you do this:

    func (s Sample) Append(name string) {
    	d := &amp;Stuff{
    		name: name,
    	}
    	s.data = append(s.data, d)
    }

Is there any reason at all why you would want to use the second example.

Defining golang struct function using pointer or not

I&#39;m trying to write some SIMD mostly for learning purposes. I know Go can link assembly, but I can&#39;t get it to work correctly.

Here&#39;s the most minimal example I can make (element-wise vector multiplication):

**vec_amd64.s** (note: the actual file has a whitespace line under `RET` since it causes errors otherwise)


    // func mul(v1, v2 Vec4) Vec4
    TEXT .mul(SB),4,$0-48
    	MOVUPS v1+0(FP),  X0
    	MOVUPS v2+16(FP), X1
    	MULPS  X1, X0
        // also tried ret+32 since I&#39;ve seen some places do that
    	MOVUPS X0, toReturn+32(FP)
    	RET


**vec.go**

    package simd
    
    type Vec4 [4]float32
    
    func (v1 Vec4) Mul(v2 Vec4) Vec4 {
    	return Vec4{v1[0] * v2[0], v1[1] * v2[1], v1[2] * v2[2], v1[3] * v2[3]}
    }
    
    func mul(v1, v2 Vec4) Vec4

**simd_test.go**

    package simd
    
    import (
    	&quot;testing&quot;
    )
    
    func TestMul(t *testing.T) {
    	v1 := Vec4{1, 2, 3, 4}
    	v2 := Vec4{5, 6, 7, 8}
    
    	res := v1.Mul(v2)
    	res2 := mul(v1, v2)
    
        // Placeholder until I get it to compile
    	if res != res2 {
    		t.Fatalf(&quot;Expected %v; got %v&quot;, res, res2)
    	}
    }

When I try to run `go test` I get the error:

    # testmain
    simd.TestMul: call to external function simd.mul
    simd.TestMul: undefined: simd.mul

The `go env` command reports my `GOHOSTARCH` to be `amd64` and my Go version to be 1.3. To confirm it wasn&#39;t the architecture causing the problem, I found another package that uses assembly and deleted all the assembly files except the `_amd64.s` one and its tests ran fine.

I also tried changing it to an exported identifier in case that was causing weirdness, but no dice. I think I pretty closely followed the template in packages like `math/big`, so hopefully it&#39;s something simple and obvious that I&#39;m missing.

I know that Go is at least **trying** to use the assembly because if I introduce a syntax error to the .s file the build tool will complain about it.

Edit:

To be clear, `go build` will compile cleanly, but `go test` causes the error to appear.

Go isn&#39;t linking my assembly: undefined external function

I have created a library by the name `libfastget` which is in the `src` with my program as 

    src
    |-libfastget
    |  |-libfastget.go
    |
    |-MainProgram
       |-main.go


and the `libfastget` exports a funtion `fastget` as follows
   

    package libfastget
    
    import (
    	&quot;fmt&quot;
    	&quot;io&quot;

    )

    
    func fastget(urlPtr *string, nPtr *int, outFilePtr *string) download {
    	.....
    	return dl
    
    }

When I use the library in my main program 

    package main
    
    import (
    	&quot;fmt&quot;
    	&quot;net/http&quot;
    	&quot;os&quot;
        &quot;libfastget&quot;
    	&quot;path/filepath&quot;
    	&quot;strings&quot;
    	&quot;flag&quot;
    	&quot;time&quot;
    
    )
    func uploadFunc(w http.ResponseWriter, r *http.Request) {
    
             n:=libfastget.fastget(url,4,filename)
    
    	}
    
    }

I get the following error upon trying to build with `go build` 

    # FServe
    ./main.go:94: cannot refer to unexported name libfastget.fastget
    ./main.go:94: undefined: libfastget.fastget

The strange thing is that the library file libfastget.a is present in the pkg folder.

Error in importing custom packages in Go Lang

In Go, what is the difference between `var s []int` and `s := make([]int, 0)`? 

I find that both works, but which one is better?

Content Type	Original Author	Original Content on Stackoverflow
Question	user3918985	View Question on Stackoverflow
Solution 1 - Mysql	VonC	View Answer on Stackoverflow
Solution 2 - Mysql	raha	View Answer on Stackoverflow
Solution 3 - Mysql	nevosial	View Answer on Stackoverflow

error connecting to database with mysqldriver

Mysql Problem Overview

Mysql Solutions

Solution 1 - Mysql

Solution 2 - Mysql

Solution 3 - Mysql

R Shiny set DataTable column width

What does this do: @RunWith(SpringJUnit4ClassRunner.class)

Attributions