Quoting the Reference Manual ([Setting the Storage Engine][1]):

&gt; If you omit the `ENGINE` option, the default storage engine is used. Normally, this is MyISAM, but you can change it by using the **`--default-storage-engine`** server startup option, or by setting the **`default-storage-engine`** option in the **`my.cnf`** configuration file.

The default-storage-engine option must be part of the mysqld section in **my.cnf**;

    [mysqld]
    default-storage-engine = innodb

You may also want to change the default storage engine just for the current session. You can do this by setting the `storage_engine` variable:

    SET storage_engine=INNODB;


  [1]: http://dev.mysql.com/doc/refman/5.1/en/storage-engine-setting.html

you need to specify the default storage engine when starting mysqld. for example:

    mysqld --default-storage-engine=InnoDB

http://dev.mysql.com/doc/refman/5.1/en/server-options.html#option_mysqld_default-storage-engine

Publishing an open-source project, is it enough to add a **COPYING** file to the package or do I need to copy and paste it on top of every project&#39;s source file?    
On famous public repositories like [github][1] or Google code I&#39;ve seen different mixed approaches so I would like to know how this aspect should be handled correctly.


  [1]: http://github.com

Open-source: licence header on each source file OR a single COPYING OR both?

What is the meaning of serialization concept in programming languages?

when we use `Serializable` attribute above a class, what is the meaning?

What is the meaning of serialization in programming languages?

I&#39;ve been working on writing SQL to create a MySQL database with several default options, including character set and collation.  Is it possible to set the default storage engine for tables in this database to InnoDB? 

I&#39;ve been looking through the MySQL 5.1 manual and I&#39;ve found the statement `ENGINE=innodb` which would be appended to a `CREATE TABLE` statement, but I haven&#39;t found anything related to a `CREATE DATABASE` statement.  

Is there a normal way to do this as part of the database creation, or does it need to be specified on a table-by-table basis?


How can I set default storage engine used by MySQL?

I've been working on writing SQL to create a MySQL database with several default options, including character set and collation. Is it possible to set the default storage engine for tables in this database to InnoDB?
I've been looking through the MySQL 5.1 manual and I've found the statement <code>ENGINE=innodb</code> which would be appended to a <code>CREATE TABLE</code> statement, but I haven't found anything related to a <code>CREATE DATABASE</code> statement.
Is there a normal way to do this as part of the database creation, or does it need to be specified on a table-by-table basis?

I&#180;d like to SELECT a single value into a variable. I&#180;d tried to following:

    DECLARE myvar INT(4);

-- immediately returns some syntax error.

    SELECT myvalue 
      FROM mytable 
     WHERE anothervalue = 1;

-- returns a single integer

    SELECT myvalue 
      INTO myvar 
      FROM mytable 
     WHERE anothervalue = 1;

-- does not work, also tried @myvar

Is possible to use DECLARE outside of stored procedures or functions?

Maybe I just dont get the concept of user variables... I just tried:

    SELECT myvalue INTO @var FROM `mytable` WHERE uid = 1;
    SELECT @var;

...which worked just like it&#180;s supposed to. But if I run each query at a time i just get @var NULL.






SELECT INTO Variable in MySQL DECLARE causes syntax error?

Does anyone know how I can take a MySQL `datetime` data type value, such as `YYYY-MM-DD HH:MM:SS` and either parse it or convert it to work in JavaScript&#39;s `Date()` function, for example:- Date(&#39;YYYY, MM, DD, HH, MM, SS);

Thank you!

Convert MySql DateTime stamp into JavaScript&#39;s Date format

I am doing `SELECT GROUP_CONCAT(categories SEPARATOR &#39; &#39;) FROM table`. Sample data below:

    categories
    ----------
    test1 test2 test3
    test4
    test1 test3
    test1 test3

However, I am getting `test1 test2 test3 test4 test1 test3` back and I would like to get `test1 test2 test3 test4` back. Any ideas?

Many thanks!

MySQL DISTINCT on a GROUP_CONCAT()

My Django unit tests take a long time to run, so I&#39;m looking for ways to speed that up. I&#39;m considering installing an [SSD][1], but I know that has its downsides too. Of course, there are things I could do with my code, but I&#39;m looking for a structural fix. Even running a single test is slow since the database needs to be rebuilt / south migrated every time. So here&#39;s my idea...

Since I know the test database will always be quite small, why can&#39;t I just configure the system to always keep the entire test database in RAM? Never touch the disk at all. How do I configure this in Django?  I&#39;d prefer to keep using [MySQL][2] since that&#39;s what I use in production, but if [SQLite][3]&amp;nbsp;3 or something else makes this easy, I&#39;d go that way.

Does SQLite or MySQL have an option to run entirely in memory? It should be possible to configure a RAM disk and then configure the test database to store its data there, but I&#39;m not sure how to tell Django / MySQL to use a different data directory for a certain database, especially since it keeps getting erased and recreated each run. (I&#39;m on a Mac FWIW.)

  [1]: http://en.wikipedia.org/wiki/Solid-state_drive
  [2]: http://en.wikipedia.org/wiki/MySQL
  [3]: http://en.wikipedia.org/wiki/SQLite




How to run Django&#39;s test database only in memory?

I have a select statement like this

    select field1, field2  
      from table1

What I want is to have a newfield with only value &quot;example&quot;.

`newfield` does not exist in the table, but when I run this query it kinda makes a virtual column with the values of example field. 

add a temporary column with a value

I have an android app that needs to check if there&#39;s already a record in the database, and if not, process some things and eventually insert it, and simply read the data from the database if the data does exist. I&#39;m using a subclass of SQLiteOpenHelper to create and get a rewritable instance of SQLiteDatabase, which I thought automatically took care of creating the table if it didn&#39;t already exist (since the code to do that is in the onCreate(...) method). 

However, when the table does NOT yet exist, and the first method ran upon the SQLiteDatabase object I have is a call to query(...), my logcat shows an error of &quot;I/Database(26434): sqlite returned: error code = 1, msg = no such table: appdata&quot;, and sure enough, the appdata table isn&#39;t being created.

Any ideas on why? 

I&#39;m looking for either a method to test if the table exists (because if it doesn&#39;t, the data&#39;s certainly not in it, and I don&#39;t need to read it until I write to it, which seems to create the table properly), or a way to make sure that it gets created, and is just empty, in time for that first call to query(...)

**EDIT**
&lt;br/&gt;
This was posted after the two answers below:
&lt;br/&gt;
I think I may have found the problem. I for some reason decided that a different SQLiteOpenHelper was supposed to be created for each table, even though both access the same database file. I think refactoring that code to only use one OpenHelper, and creating both tables inside it&#39;s onCreate may work better...

How does one check if a table exists in an Android SQLite database?

When dealing with big databases, which performs better, `IN` or `OR` in the SQL `Where`-clause?

Is there any difference about the way they are executed?

IN vs OR in the SQL WHERE Clause

I am trying to understand a paper on concurrent B-tree, in which the author mentioned latch vs lock, and how latches do not need a &quot;Lock Manager&quot;. I have been trying to figure out what are differences between those two for two days.

Google resulting in:

&quot;locks assure logical consistency of data.  They are implemented via a lock table, held for a long time (e.g. 2PL), and part of the deadlock detection mechanism.

latches are like semaphores. They assure physical consistency of data and resources, which are not visible at the transactional level&quot;

However, I am still pretty confused. Can some one elaborate on this? and what exactly does a lock manager do? 

Thanks in advance.

What is the difference between a lock and a latch in the context of concurrent access to a database?

Why do we always need to specify `VARCHAR(length)` instead of just `VARCHAR`? It is dynamic anyway.

UPD: I&#39;m puzzled specifically by the fact that it is mandatory (e.g. in MySQL).

Why does VARCHAR need length specification?

I am getting the following error while trying to add a NOT NULL column to an existing table. Why is it happening ?. I tried rake db:reset thinking that the existing records are the problem, but even after resetting the DB, the problem persists. Can you please help me figure this out.

&lt;!-- language-all: lang-ruby --&gt;

 **Migration File**

    class AddDivisionIdToProfile &lt; ActiveRecord::Migration
      def self.up
        add_column :profiles, :division_id, :integer, :null =&gt; false
      end
    
      def self.down
        remove_column :profiles, :division_id
      end
    end

**Error Message**

&gt; SQLite3::SQLException: Cannot add a NOT NULL column with default value NULL: ALTER TABLE &quot;profiles&quot; ADD &quot;division_id&quot; integer NOT NULL



Cannot add a NOT NULL column with default value NULL in Sqlite3

I get this error message:

&gt; ERROR 1217 (23000) at line 40: Cannot
&gt; delete or update a parent row: a
&gt; foreign key constraint fails

... when I try to drop a table:

    DROP TABLE IF EXISTS `area`;

... defined like this:

    CREATE TABLE `area` (
      `area_id` char(3) COLLATE utf8_spanish_ci NOT NULL,
      `nombre_area` varchar(30) COLLATE utf8_spanish_ci NOT NULL,
      `descripcion_area` varchar(100) COLLATE utf8_spanish_ci NOT NULL,
      PRIMARY KEY (`area_id`),
      UNIQUE KEY `nombre_area_UNIQUE` (`nombre_area`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_spanish_ci;

The funny thing is that **I already dropped all other tables** in the schema that have foreign keys against `area`. Actually, the database is empty except for the `area` table.

How can it possibly have child rows if there isn&#39;t any other object in the database? As far as I know, InnoDB doesn&#39;t allow foreign keys on other schemas, does it?

(I can even run a `RENAME TABLE area TO something_else` command :-?)

Bogus foreign key constraint fail

I am using MySQL in localhost as a &quot;query tool&quot; for performing statistics in R, that is, everytime I run a R script, I create a new database (A), create a new table (B), import the data into B, submit a query to get what I need, and then I drop B and drop A.

It&#39;s working fine for me, but I realize that the ibdata file size is increasing rapidly, I stored nothing in MySQL, but the ibdata1 file already exceeded 100 MB.

I am using more or less default MySQL setting for the setup, is there a way for I can automatically shrink/purge the ibdata1 file after a fixed period of time?

How to shrink/purge ibdata1 file in MySQL

Is there a nice easy way to drop all tables from a MySQL database, ignoring any foreign key constraints that may be in there?

MySQL DROP all tables, ignoring foreign keys

What is `InnoDB` and `MyISAM` in `MySQL` ?

What is InnoDB and MyISAM in MySQL?

I know I can issue an alter table individually to change the table storage from MyISAM to InnoDB.

I am wondering if there is a way to quickly change all of them to InnoDB?

Content Type	Original Author	Original Content on Stackoverflow
Question	memilanuk	View Question on Stackoverflow
Solution 1 - Mysql	Daniel Vassallo	View Answer on Stackoverflow
Solution 2 - Mysql	sml	View Answer on Stackoverflow

How can I set default storage engine used by MySQL?

Mysql Problem Overview

Mysql Solutions

Solution 1 - Mysql

Solution 2 - Mysql

What is the meaning of serialization in programming languages?

Open-source: licence header on each source file OR a single COPYING OR both?

Attributions