Kategorie: Programmierung

Programmierung von PHP, Javascript, (X)HTML/CSS und anderem.

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„//“ prefix in urls anchor hrefs (protocol relative url)

Beginning an url (anchor href/img source/ …) with „//“ is called protocol relative url and is defined within the RFC 3986.

Using this link notation is helpful if your link must (or should)  use the same protocol as the displayed page.

Examples:

  1. User visits http://www.example.com, all links or image resources should be referenced to the same protocol http.
  2. User visits https://www.example.com, all links or image resources should be referenced to the same protocol https.

A protocol relative url is not restricted to the same url – you may use it to link/refer to other urls as well.

 

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Compare a set of database table data on different servers

How may you validate, that data on different databases equal each other?
Execute the following (mysql) query on each database. You will get an MD5 string which is easily to be compared.

SELECT MD5( SUM( ch ) )
FROM (
SELECT crc32( MD5( CONCAT_WS( ',',
field1, field2, field3
) ) ) AS ch
FROM tablename
WHERE field0 = 3
)a

PS: Insert into the field list only fields which should be compared.
E.g. Do not include auto increment or timestamp/date columns if they are allowed to be different on each database!