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• There is a new table: variable_type - it describes possible types of the variables
• Inside variable table, there is no longer variable_type column. Instead there is a foreign key (variable_type_id) that points at variable_type.id
• There is a new table: request_status - it describes possible statues of the request
• Inside request table there is no longer status column - instead there is a foreign key (request_status_id) that points at request_status.id

Refined schema (step 9)

Filter table

• There is a new table: filter - it allows to store custom user filters
• There is a new table: user_filter - it allows to link filter with user; it is possible to share filter between different user - this is why filters require linking table between user and filter

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