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;

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)

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)

Dump MySQL file of database table schema (structure)

admin — Wed, 18 Feb 2009 18:23:54 +0000

To dump an SQL file of just the schema (structure) of a MySQL database table you can use this command line:

1	mysqldump -du username -p databasename tablename > filename.sql

You can drop the -p if you don’t have a password.

Useful if you need to move table structures around ;]

MySQL search and replace query

admin — Thu, 22 Jan 2009 12:51:39 +0000

For my own records:

1	UPDATE tablename SET tablefield = REPLACE(tablefield,"findstring","replacestring");

MySQL export SQL query as file

admin — Sun, 18 Jan 2009 10:35:00 +0000

This will dump an SQL statement into a file:

1	mysql -u username -p database_name -e "SQL_STATEMENT" > file.data

64bit PHP 5.2.5 compile error (Fedora Core 8)

admin — Sun, 23 Mar 2008 18:53:50 +0000

I recently moved over to the 64bit version of Fedora Core 8.

My plan was to compile both Apache and PHP from source, as they require a fair amount of customisations for my needs.

The Apache compile went without problems but using my regular configure directives for PHP (5.2.5) threw this error:

1	configure: error: mysql configure failed. Please check config.log for more information.

This confused me a little and I spent quite some time investigating possible issues with MySQL. The config.log was pretty useless!

After a fair amount of reading I came across this directive that solved the issue (should have known!):

1	--with-libdir=lib64

So my final configure command looked like this:

1	./configure --with-apxs2=/usr/local/apache2/bin/apxs --with-libdir=lib64 --with-mysql --with-zlib-dir=/usr/include/ --with-openssl --with-curl --with-config-file-path=/etc/php.ini

No more errors! Joy ;]