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   title       = {PostgreSQL: Documentation: Manuals: PostgreSQL 8.2: PostgreSQL 8.2.17 Documentation}, 
   url         = {http://www.postgresql.org/docs/8.2/static/index.html},
   biburl      = {https://puma.uni-kassel.de/url/fd25ae9e9a7ea3cabda42dedb0e4b00b/stephandoerfel},
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@electronic{dev.mysql.com,
   title       = {MySQL :: MySQL 5.1 Referenzhandbuch :: 3.3.4.9 Mehr als eine Tabelle benutzen}, 
   url         = {http://dev.mysql.com/doc/refman/5.1/de/multiple-tables.html},
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