In 5.7.6 and above, you should be able to use [`CREATE USER`][1]

    CREATE USER IF NOT EXISTS &#39;user&#39;@&#39;localhost&#39; IDENTIFIED BY &#39;password&#39;;

Note that the 5.7.6 method doesn&#39;t actually grant any permissions.

---

If you aren&#39;t using a version which has this capability (something below 5.7.6), you can do the following:

    GRANT ALL ON `database`.* TO &#39;user&#39;@&#39;localhost&#39; IDENTIFIED BY &#39;password&#39;;

This will create the user if it doesn&#39;t exist

---

Note, if you are on MySQL 8, the `GRANT ALL` method will not create a user.



  [1]: http://dev.mysql.com/doc/refman/5.7/en/create-user.html

I use

SELECT EXISTS (SELECT DISTINCT `user` FROM `mysql`.`user` WHERE `user` = &quot;username&quot;) as is_user

should return 1 if exists or 0 if it does not

I have model that looks like this:

    class Category(models.Model):
        parentCategory = models.ForeignKey(&#39;self&#39;, blank=True, null=True, related_name=&#39;subcategories&#39;)
        name = models.CharField(max_length=200)
        description = models.CharField(max_length=500)

I managed to get flat json representation of all categories with serializer:

    class CategorySerializer(serializers.HyperlinkedModelSerializer):
        parentCategory = serializers.PrimaryKeyRelatedField()
        subcategories = serializers.ManyRelatedField()

        class Meta:
            model = Category
            fields = (&#39;parentCategory&#39;, &#39;name&#39;, &#39;description&#39;, &#39;subcategories&#39;)

Now what I want to do is for subcategories list to have inline json representation of subcategories instead of their ids. How would I do that with django-rest-framework? I tried to find it in documentation, but it seems incomplete.



Django rest framework nested self-referential objects

I have a form on one page that submits to another page. There, it checks if the input `mail` is filled. If so then do something and if it is not filled, do something else. I don&#39;t understand why it always says that it is set, even if I send an empty form. What is missing or wrong?

`step2.php`:
  
    &lt;form name=&quot;new user&quot; method=&quot;post&quot; action=&quot;step2_check.php&quot;&gt; 
        &lt;input type=&quot;text&quot; name=&quot;mail&quot;/&gt; &lt;br /&gt;
        &lt;input type=&quot;password&quot; name=&quot;password&quot;/&gt;&lt;br /&gt;
        &lt;input type=&quot;submit&quot;  value=&quot;continue&quot;/&gt;
    &lt;/form&gt;

`step2_check.php`:

    if (isset($_POST[&quot;mail&quot;])) {
    	echo &quot;Yes, mail is set&quot;;	
    } else {	
    	echo &quot;N0, mail is not set&quot;;
    }

If isset $_POST

I have a query to check mysql users list for create new user.

    IF (SELECT EXISTS(SELECT 1 FROM `mysql`.`user` WHERE `user` = &#39;{{ title }}&#39;)) = 0 THEN
    	CREATE USER &#39;{{ title }}&#39;@&#39;localhost&#39; IDENTIFIED BY &#39;{{ password }}&#39;
    END IF;

But i get this error:

    ERROR 1064 (42000) at line 3: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near &#39;IF (SELECT EXISTS(SELECT 1 FROM `mysql`.`user` WHERE `user` = &#39;cms_localhost&#39;)) = 0 &#39; at line 1



mysql create user if not exists

I have a query to check mysql users list for create new user.
<pre><code class="hljs language-sql">IF (SELECT EXISTS(SELECT 1 FROM `mysql`.`user` WHERE `user` = '{{ title }}')) = 0 THEN
	CREATE USER '{{ title }}'@'localhost' IDENTIFIED BY '{{ password }}'
END IF;
</code></pre>
But i get this error:
<pre><code class="hljs language-scss">ERROR 1064 (42000) at line 3: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF (SELECT EXISTS(SELECT 1 FROM `mysql`.`user` WHERE `user` = 'cms_localhost')) = 0 ' at line 1
</code></pre>

I was suggested, not long ago, to change my code to use PDO in order to parameterize my queries and safely save HTML in the database.

Well, here are the main problems:

 1. I looked at &lt;http://php.net/manual/en/ref.pdo-mysql.php&gt;, and I don&#39;t really get where I should put that `$ ./configure --with-pdo-mysql` string...

 2. The site I&#39;m building actually only requires PDO for one page. While I may consider re-writing it, it would take a while and I need the pages to be running soon, so I can&#39;t turn off MySQL completely. If I do install PDO, will I still be able to use `mysql_*` handlers?

The server in question is running PHP Version 5.4.6-1ubuntu1 and Apache/2.2.22 (Ubuntu). I&#39;m also running a phpMyAdmin database, if it matters.



Installing PDO driver on MySQL Linux server

No idea what is going on here.  Here is the query, right from phpMyAdmin:

    SELECT * FROM `la_schedule` WHERE &#39;start_date&#39; &gt;&#39;2012-11-18&#39;;

But I consistently get all records in the table returned, including those with start date 2012-11-01.  What gives?

How to use greater than operator with date?

If I have a table with the following data in MySQL:

    id       Name       Value
    1          A          4
    1          A          5
    1          B          8
    2          C          9

how do I get it into the following format?

    id         Column
    1          A:4,5,B:8
    2          C:9

&lt;br&gt;
I think I have to use `GROUP_CONCAT`. But I&#39;m not sure how it works.

How to use GROUP_CONCAT in a CONCAT in MySQL

When selecting from multiple tables in MySQL, both of the following queries return the same result set.

Is one of these queries _better_ or more efficient than the other? From my testing on a small dataset (~2k rows in each table) they both return the same result set in around the same execution time.

**Query 1:**

    SELECT
        *
    FROM
        products,
        product_meta,
        sales_rights
    WHERE 
        (
            products.id = product_meta.product_id
            AND products.id = sales_rights.product_id
        )
        AND (...)
    LIMIT 0,10;
&lt;br /&gt;
**Query 2:**

    SELECT
        *
    FROM
        products
    INNER JOIN product_meta ON products.id = product_meta.product_id
    JOIN sales_rights ON product_meta.product_id = sales_rights.product_id 
    WHERE
        (...)
    LIMIT 0,10;


Multiple Table Select vs. JOIN (performance)

What am I doing wrong here? I&#39;m simply retrieving results from a table and then adding them to an array. Everything works as expected until I check for an empty result...

This gets the match, adds it to my array and echoes the result as expected:

    $today = date(&#39;Y-m-d&#39;, strtotime(&#39;now&#39;));

    $sth = $db-&gt;prepare(&quot;SELECT id_email FROM db WHERE hardcopy = &#39;1&#39; AND hardcopy_date &lt;= :today AND hardcopy_sent = &#39;0&#39; ORDER BY id_email ASC&quot;);

    $sth-&gt;bindParam(&#39;:today&#39;, $today, PDO::PARAM_STR);

    if(!$sth-&gt;execute()) {
        $db = null;
        exit();
    }

    while ($row = $sth-&gt;fetch(PDO::FETCH_ASSOC)) {
        $this-&gt;id_email[] = $row[&#39;id_email&#39;];
        echo $row[&#39;id_email&#39;];
    }

    $db = null;
    return true;

When I try to check for an empty result, my code returns &#39;empty&#39;, but no longer yields the matching result:

    $today = date(&#39;Y-m-d&#39;, strtotime(&#39;now&#39;));

    $sth = $db-&gt;prepare(&quot;SELECT id_email FROM db WHERE hardcopy = &#39;1&#39; AND hardcopy_date &lt;= :today AND hardcopy_sent = &#39;0&#39; ORDER BY id_email ASC&quot;);

    $sth-&gt;bindParam(&#39;:today&#39;,$today, PDO::PARAM_STR);

    if(!$sth-&gt;execute()) {
        $db = null;
        exit();
    }

    if ($sth-&gt;fetchColumn()) {
        echo &#39;not empty&#39;;
        while ($row = $sth-&gt;fetch(PDO::FETCH_ASSOC)) {
            $this-&gt;id_email[] = $row[&#39;id_email&#39;];
            echo $row[&#39;id_email&#39;];
        }
        $db = null;
        return true;
    }
    echo &#39;empty&#39;;
    $db = null;
    return false;


Checking for an empty result (PHP, PDO, and MySQL)

In the [documentation][0], there is an example of using the `lineinfile` module to edit `/etc/sudoers`.   

    - lineinfile: &quot;dest=/etc/sudoers state=present regexp=&#39;^%wheel&#39; line=&#39;%wheel ALL=(ALL) NOPASSWD: ALL&#39;&quot;

Feels a bit hackish. 

I assumed there would be something in the `user` module to handle this but there doesn&#39;t appear to be any options.

What are the best practices for adding and removing users to `/etc/sudoers`?

[0]:http://docs.ansible.com/ansible/lineinfile_module.html

Content Type	Original Author	Original Content on Stackoverflow
Question	sweb	View Question on Stackoverflow
Solution 1 - Mysql	Ascherer	View Answer on Stackoverflow
Solution 2 - Mysql	ingocnito	View Answer on Stackoverflow

mysql create user if not exists

Mysql Problem Overview

Mysql Solutions

Solution 1 - Mysql

Solution 2 - Mysql

If isset $_POST

Django rest framework nested self-referential objects

Attributions