It turns out I was just missing `DECIMAL` on the `CAST()` description:

&gt;**`DECIMAL[(M[,D])]`**
&gt;
&gt;Converts a value to DECIMAL data type. The optional arguments M and D specify the precision (M specifies the total number of digits) and the scale (D specifies the number of digits after the decimal point) of the decimal value. The default precision is two digits after the decimal point.

Thus, the following query worked:

    UPDATE table SET
    latitude = CAST(old_latitude AS DECIMAL(10,6)),
    longitude = CAST(old_longitude AS DECIMAL(10,6));

    mysql&gt; SELECT CAST(4 AS DECIMAL(4,3));
    +-------------------------+
    | CAST(4 AS DECIMAL(4,3)) |
    +-------------------------+
    |                   4.000 |
    +-------------------------+
    1 row in set (0.00 sec)
    
    mysql&gt; SELECT CAST(&#39;4.5s&#39; AS DECIMAL(4,3));
    +------------------------------+
    | CAST(&#39;4.5s&#39; AS DECIMAL(4,3)) |
    +------------------------------+
    |                        4.500 |
    +------------------------------+
    1 row in set (0.00 sec)
    
    mysql&gt; SELECT CAST(&#39;a4.5s&#39; AS DECIMAL(4,3));
    +-------------------------------+
    | CAST(&#39;a4.5s&#39; AS DECIMAL(4,3)) |
    +-------------------------------+
    |                         0.000 |
    +-------------------------------+
    1 row in set, 1 warning (0.00 sec)

This will convert to a numeric value without the need to cast or specify length or digits:

`STRING_COL+0.0`

If your column is an `INT`, can leave off the `.0` to avoid decimals:

`STRING_COL+0`

How do I know which is the default measure system (imperial or metric) on iOS ?

How do I get this preference from the device settings, so I know what to display in my app ?

thanks

How do I know which is the default measure system (imperial or metric) on iOS?

I am learning about databases and SQL for the first time.  In the text I&#39;m reading (Oracle 11g: SQL by Joan Casteel), it says that &quot;many-to-many relationships can&#39;t exist in a relational database.&quot; I understand that we are to avoid them, and I understand how to create a bridging entity to eliminate them, but I am trying to fully understand the statement &quot;can&#39;t exist.&quot;

Is it actually physically impossible to have a many-to-many relationship represented?

Or is it just very inefficient since it leads to a lot of data duplication?

It seems to me to be the latter case, and the bridging entity minimizes the duplicated data. But maybe I&#39;m missing something? I haven&#39;t found a concrete reason (or better yet an example) that explains why to avoid the many-to-many relationship, either in the text or anywhere else I&#39;ve searched.  I&#39;ve been searching all day and only finding the same information repeated: &quot;don&#39;t do it, and use a bridging entity instead.&quot;  But I like to ask why. :-)

Thanks! 

Why no many-to-many relationships?

I have a table containing latitude and longitude values stored as strings (`VARCHAR`) which I&#39;d like to convert to `FLOAT (10,6)`.

However there doesn&#39;t appear to be a straightforward way to do this using `CAST()` or `CONVERT()`.

How can I convert these columns easily? This is a one-time conversion.

How can I convert a string to a float in mysql?

I have a table containing latitude and longitude values stored as strings (<code>VARCHAR</code>) which I'd like to convert to <code>FLOAT (10,6)</code>.
However there doesn't appear to be a straightforward way to do this using <code>CAST()</code> or <code>CONVERT()</code>.
How can I convert these columns easily? This is a one-time conversion.

I have a ~10M record MySQL table that I interface with using SqlAlchemy.  I have found that queries on large subsets of this table will consume too much memory even though I thought I was using a built-in generator that intelligently fetched bite-sized chunks of the dataset:

    for thing in session.query(Things):
        analyze(thing)

To avoid this, I find I have to build my own iterator that bites off in chunks:

    lastThingID = None
    while True:
        things = query.filter(Thing.id &lt; lastThingID).limit(querySize).all()
        if not rows or len(rows) == 0: 
            break
        for thing in things:
            lastThingID = row.id
            analyze(thing)

Is this normal or is there something I&#39;m missing regarding SA built-in generators?

The answer to [this question][1] seems to indicate that the memory consumption is not to be expected.


  [1]: https://stackoverflow.com/questions/1078383/sqlalchemy-difference-between-query-and-query-all-in-for-loops

memory-efficient built-in SqlAlchemy iterator/generator?

Someone sent me a SQL query where the `GROUP BY` clause consisted of the statement: `GROUP BY 1`.

This must be a typo right? No column is given the alias 1. What could this mean? Am I right to assume that this must be a typo?

What does SQL clause &quot;GROUP BY 1&quot; mean?

I have the following error with one of our web applications - 

    Query3 failed: Error writing file &#39;/tmp/MY1fnqpm&#39; (Errcode: 28) ... INSERT MailList... (removed the rest of the query for security reasons)

Any ideas - is this some hard disk space issue on my server?

MySQL/Writing file error (Errcode 28)

Here&#39;s my simple SQL question...

I have two tables:

Books

    -------------------------------------------------------
    | book_id | author | genre | price | publication_date |
    -------------------------------------------------------

Orders

    ------------------------------------
    | order_id | customer_id | book_id |
    ------------------------------------

I&#39;d like to create a query that returns:

    --------------------------------------------------------------------------
    | book_id | author | genre | price | publication_date | number_of_orders |
    --------------------------------------------------------------------------

In other words, return every column for **ALL** rows in the Books table, along with a calculated column named &#39;number_of_orders&#39; that counts the number of times each book appears in the Orders table. (If a book does not occur in the orders table, the book **should** be listed in the result set, but &quot;number_of_orders&quot; should be **zero**.

So far, I&#39;ve come up with this:

    SELECT
        books.book_id,
        books.author,
        books.genre,
        books.price,
        books.publication_date,
        count(*) as number_of_orders
    from books
    left join orders
    on (books.book_id = orders.book_id)
    group by
        books.book_id,
        books.author,
        books.genre,
        books.price,
        books.publication_date

That&#39;s *almost* right, but not quite, because &quot;number_of_orders&quot; will be 1 even if a book is never listed in the Orders table. Moreover, given my lack of knowledge of SQL, I&#39;m sure this query is very inefficient.

What&#39;s the right way to write this query? (For what it&#39;s worth, this needs to work on MySQL, so I can&#39;t use any other vendor-specific features).

Thanks in advance!

How to count the number of instances of each foreign-key ID in a table?

When I run `show status like &#39;Con%&#39;` it shows the number of connections, which is 9972 and constantly growing. Is this an active number of connections or connections made in total?

MySQL show status - active or total connections?

How could I convert from float to string or string to float?
  
In my case I need to make the assertion between 2 values string (value that I have got from table) and float value that I have calculated.

    String valueFromTable = &quot;25&quot;;
    Float valueCalculated =25.0;

I tried from float to string:
 
    String sSelectivityRate = String.valueOf(valueCalculated);

but the assertion fails 


Convert float to String and String to float in Java

I have a variable that stores `false` or `true`, but I need `0` or `1` instead, respectively. How can I do this?

Convert boolean result into number/integer

    #include&lt;stdio.h&gt;
    #include&lt;string.h&gt;
    
    int main() 
    {
    	char s[100] =&quot;4.0800&quot; ; 
    
    	printf(&quot;float value : %4.8f\n&quot; ,(float) atoll(s)); 
    	return 0; 
    }


I expect the output should be `4.08000000` whereas I got only `4.00000000`.

Is there any way to get the numbers after the dot?

How to convert string to float?

I&#39;ve tried implementing a function like this, but unfortunately it doesn&#39;t work:

    const wchar_t *GetWC(const char *c)
    {
        const size_t cSize = strlen(c)+1;
        wchar_t wc[cSize];
        mbstowcs (wc, c, cSize);

        return wc;
    }

My main goal here is to be able to integrate normal char strings in a Unicode application. Any advice you guys can offer is greatly appreciated.

How to convert char* to wchar_t*?

I have a `char` and I need a `String`. How do I convert from one to the other?

Content Type	Original Author	Original Content on Stackoverflow
Question	JYelton	View Question on Stackoverflow
Solution 1 - Mysql	JYelton	View Answer on Stackoverflow
Solution 2 - Mysql	zloctb	View Answer on Stackoverflow
Solution 3 - Mysql	Justas	View Answer on Stackoverflow

How can I convert a string to a float in mysql?

Mysql Problem Overview

Mysql Solutions

Solution 1 - Mysql

Solution 2 - Mysql

Solution 3 - Mysql

Why no many-to-many relationships?

How do I know which is the default measure system (imperial or metric) on iOS?

Attributions