Web Development & Stuff » MySQL

Mysql multiple conditional joins with conditional select

admin — Sat, 15 May 2010 09:18:10 +0000

For my own records but may also be of interest to some…

This statement performs 4 conditional left outer joins and then uses CASE to conditionally select the returned columns as a single group of columns.

So a polymorphic one to one relationship is returned in a single query.

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$sql = <<
SELECT *, ELT(Log.action,'$elt_list') AS what,

 CASE WHEN Friend.source_type = '$typeVisitor' THEN 'Anonymous Visitor' WHEN Friend.source_type = '$typeRecipient' THEN 'Referrer' WHEN Friend.source_type = '$typeDiVisitor' THEN 'DI visitor' WHEN Friend.source_type = '$typeFriend' THEN 'Friend' ELSE NULL END as 'source',

 CASE WHEN Friend.source_type = '$typeVisitor' THEN Visitor.title WHEN Friend.source_type = '$typeRecipient' THEN Recipient.title WHEN Friend.source_type = '$typeDiVisitor' THEN DiVisitor.title WHEN Friend.source_type = '$typeFriend' THEN RefFriend.title ELSE NULL END as 'Source.title',

 CASE WHEN Friend.source_type = '$typeVisitor' THEN Visitor.firstname WHEN Friend.source_type = '$typeRecipient' THEN Recipient.firstname WHEN Friend.source_type = '$typeDiVisitor' THEN DiVisitor.firstname WHEN Friend.source_type = '$typeFriend' THEN RefFriend.firstname ELSE NULL END as 'Source.firstname',

 CASE WHEN Friend.source_type = '$typeVisitor' THEN Visitor.surname WHEN Friend.source_type = '$typeRecipient' THEN Recipient.surname WHEN Friend.source_type = '$typeDiVisitor' THEN DiVisitor.surname WHEN Friend.source_type = '$typeFriend' THEN RefFriend.surname ELSE NULL END as 'Source.surname',

 CASE WHEN Friend.source_type = '$typeVisitor' THEN Visitor.email WHEN Friend.source_type = '$typeRecipient' THEN Recipient.email WHEN Friend.source_type = '$typeDiVisitor' THEN DiVisitor.email WHEN Friend.source_type = '$typeFriend' THEN RefFriend.email ELSE NULL END as 'Source.email'

 FROM friends AS Friend 

 LEFT OUTER JOIN visitors AS Visitor ON (Visitor.id = Friend.source_id) AND (Friend.source_type = '$typeVisitor')

 LEFT OUTER JOIN visitors AS Recipient ON (Recipient.id = Friend.source_id) AND (Friend.source_type = '$typeRecipient')

 LEFT OUTER JOIN di_visitors AS DiVisitor ON (DiVisitor.id = Friend.source_id) AND (Friend.source_type = '$typeDiVisitor')

 LEFT OUTER JOIN friends AS RefFriend ON (RefFriend.id = Friend.source_id) AND (Friend.source_type = '$typeFriend'),

 log_table AS Log

 WHERE Log.model_id=Friend.id AND Log.type=$tf

SQL;

MySQL query with nested statement in parent where clause

admin — Mon, 16 Nov 2009 17:24:16 +0000

Quick reminder for myself of how to do a nested MySQL query with the nested statement in the parent where clause:

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$sql = <<
SELECT id

 FROM invoices as Invoice

 WHERE id NOT IN (

  SELECT parent_id 

  FROM invoices 

  WHERE parent_id > 0

  GROUP BY parent_id    

 ) AND billing_start <= '$end'

SQL;

CakePHP schema generate doesn’t like MySQL enum columns

admin — Thu, 05 Nov 2009 20:04:03 +0000

Tried to do a schema snapshot of my db today (cake schema generate) to throw in SVN. I’d added an enum column to one of my tables and it threw this error:

1	Notice: Schema generation error: invalid column type enum('flat_fee','per_unit') does not exist in DBO in /vhosts/site.com/accounts/cake/libs/model/schema.php on line 475

Enum must be too old-school and crusty these days!! I guess I could have used an boolean tinyint(1) (or a keyed association) but there’s something nice and readable about poor old simple innocent enum….. *tears*

Query MySQL for records that were created within the last 7 days/week

admin — Fri, 02 Oct 2009 15:22:44 +0000

You can use this in your MySQL WHERE clause to return records that were created within the last 7 days/week:

1	created >= DATE_SUB(CURDATE(),INTERVAL 7 day)

You can also use NOW() in the subtraction to give hh:mm:ss resolution. So to return records created exactly (to the second) within the last 24hrs, you could do:

1	created >= DATE_SUB(NOW(),INTERVAL 1 day)

CakePHP plugin view overriding

admin — Thu, 27 Aug 2009 16:47:24 +0000

Woo hoo! It’s possible to override CakePHP plugin views just like in Rails using the Engines plugin. Documentation on how to do it is a bit thin on the ground though.

Say you created a CakePHP plugin called ‘cms’ and you had a plugin controller called ‘pages’ inside the cms plugin. Just place the views you want to override in:

1	/app/views/plugins/cms/pages/

I’ll post again when I’ve had a play at extending plugin controllers and models from the main app folder.

Reset PHP array key values

admin — Sat, 16 May 2009 11:17:19 +0000

To reset the key values in a PHP array you can do this:

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$things = array('a','b','c','d');

unset($things[0]);

print_r($things); 

#outputs

#Array

#(

#    [1] => b

#    [2] => c

#    [3] => d

#)

# Actually do the reset.

$things = array_values($things);

print_r($things);

#outputs 

#Array

#(

#    [0] => b

#    [1] => c

#    [2] => d

#)

Dynamic object attributes / member variables with specific visibility not possible with PHP

admin — Wed, 06 May 2009 09:48:53 +0000

Ran into an interesting situation yesterday. I wanted to create some dynamic (overloading) object attributes (object member variables) in PHP with private visibility. Forcing encapsulation via getter methods. It seems this is not possible, as dynamic attributes are only ever public (see the PHP documentation).

There is however, as always, a work around! If you set a private containing array for your dynamic attributes you can get almost the same behaviour:

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class TestClass {

    private $dynamic_attribute_container = array();

    # This method is used to set new attributes.

    public SettingMethod($variable_name, $variable_value){

        $this->dynamic_attribute_container[$this->variable_name] = $this->variable_value;

    }

    # This method is used to return the attributes from within the private array container.

    public GettingMethod($attribute_name){

        # Encapsulation code.

        $output = strtolower($this->dynamic_attribute_container[$attribute_name]);

        return $output;

    }

}

$object = new TestClass();

$object->SettingMethod('foo','bar');

$object->foo; # This will error.

$object->GettingMethod('foo'); # This will return bar.

If anyone else has any thoughts on this subject I’d love to hear them.

MySQL indexes – query performance increase

admin — Wed, 25 Feb 2009 11:54:41 +0000

Today I had a log table report query that contained a nested query. It was taking ages (5mins) to complete. I investigated indexes which I had been meaning to look at for a while. Anyway I managed to bring down the query to 0.04s – I now have much love for indexes!!

Basic MySQL syntax:

1	CREATE INDEX index_name ON table_name(column_name);

You can also create indexes when you create a table. In this example I’m indexing id,landing_id,page_id and action_id with INDEX (id,landing_id,page_id,action_id):

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CREATE TABLE IF NOT EXISTS visitor_actions (

  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,

  landing_id INT UNSIGNED NOT NULL,

  page_id TINYINT UNSIGNED NOT NULL,

  action_id TINYINT UNSIGNED NOT NULL,

  dwell_time MEDIUMINT UNSIGNED NULL,

  start TINYINT UNSIGNED NOT NULL,

  created_at DATETIME NOT NULL,

  INDEX (id,landing_id,page_id,action_id)

) ENGINE=INNODB;

I’ll add to this post when I spend some more time looking at the different index types.

MySQL TIMEDIFF calculate time difference in query

admin — Tue, 24 Feb 2009 15:20:22 +0000

Handy, brings you back a time difference in hh:mm:ss format inside an MySQL query:

1	TIMEDIFF(date_time_one, date_time_two)