You are now a sqlite data analyst, and you are given a database schema as follows:

    【Schema】
    【DB_ID】 student_club
【Schema】
# Table: major
[
(major_id:TEXT, Primary Key, Examples: [rec06DF6vZ1CyPKpc, rec09LedkREyskCNv, rec0Eanv576RhQllI]),
(major_name:TEXT, Examples: [Outdoor Product Design and Development]),
(department:TEXT),
(college:TEXT, Examples: [College of Agriculture and Applied Sciences])
]
# Table: budget
[
(budget_id:TEXT, Primary Key, Examples: [rec0QmEc3cSQFQ6V2, rec1bG6HSft7XIvTP, rec1z6ISJU2HdIsVm]),
(category:TEXT, Examples: [Advertisement, Food, Speaker Gifts]),
(spent:REAL, Examples: [67.81, 121.14, 20.2]),
(remaining:REAL, Examples: [7.19, 28.86, -0.199999999999999]),
(amount:INTEGER, Examples: [75, 150, 20]),
(event_status:TEXT, Examples: [Closed, Open, Planning]),
(link_to_event:TEXT, Examples: [recI43CzsZ0Q625ma, recggMW2eyCYceNcy, recJ4Witp9tpjaugn])
]
# Table: member
[
(member_id:TEXT, Primary Key, Examples: [rec1x5zBFIqoOuPW8, rec280Sk7o31iG0Tx, rec28ORZgcm1dtqBZ]),
(first_name:TEXT, Examples: [Angela, Grant, Luisa]),
(last_name:TEXT, Examples: [Sanders, Gilmour, Guidi]),
(email:TEXT),
(position:TEXT, Examples: [Member, Inactive, President]),
(t_shirt_size:TEXT, Examples: [Medium, X-Large, Large]),
(phone:TEXT, Examples: [(651) 928-4507, 403-555-1310, 442-555-5882]),
(zip:INTEGER, Examples: [55108, 29440, 10002]),
(link_to_major:TEXT, Examples: [recxK3MHQFbR9J5uO, rec7BxKpjJ7bNph3O, recdIBgeU38UbV2sy])
]
# Table: zip_code
[
(zip_code:INTEGER, Primary Key, Examples: [501, 544, 601]),
(type:TEXT, Examples: [Unique, Standard, PO Box]),
(city:TEXT, Examples: [Holtsville, Adjuntas, Aguada]),
(county:TEXT, Examples: [Suffolk County, Adjuntas Municipio, Aguada Municipio]),
(state:TEXT, Examples: [New York, Puerto Rico, Massachusetts]),
(short_state:TEXT, Examples: [NY, PR, MA])
]
# Table: income
[
(income_id:TEXT, Primary Key, Examples: [rec0s9ZrO15zhzUeE, rec7f5XMQZexgtQJo, rec8BUJa8GXUjiglg]),
(date_received:TEXT, Examples: [2019-10-17, 2019-09-04, 2019-10-08]),
(amount:INTEGER, Examples: [50, 200, 3000]),
(source:TEXT, Examples: [Dues, Fundraising, School Appropration]),
(notes:TEXT),
(link_to_member:TEXT, Examples: [reccW7q1KkhSKZsea, recTjHY5xXhvkCdVT, recUdRhbhcEO1Hk5r])
]
# Table: attendance
[
(link_to_event:TEXT, Primary Key, Examples: [rec2N69DMcrqN9PJC, rec5XDvJLyxDsGZWc, recEVTik3MlqbvLFi]),
(link_to_member:TEXT, Primary Key, Examples: [recD078PnS3x2doBe, recP6DJPyi5donvXL, rec28ORZgcm1dtqBZ])
]
# Table: expense
[
(expense_id:TEXT, Primary Key, Examples: [rec017x6R3hQqkLAo, rec1nIjoZKTYayqZ6, rec1oMgNFt7Y0G40x]),
(expense_description:TEXT, Examples: [Post Cards, Posters, Water, Cookies, Pizza]),
(expense_date:TEXT, Examples: [2019-08-20, 2019-10-08, 2019-09-10]),
(cost:REAL, Examples: [122.06, 20.2, 51.81]),
(approved:TEXT, Examples: [true]),
(link_to_member:TEXT, Examples: [rec4BLdZHS2Blfp4v, recro8T1MPMwRadVH, recD078PnS3x2doBe]),
(link_to_budget:TEXT, Examples: [recvKTAWAFKkVNnXQ, recy8KY5bUdzF81vv, recwXIiKoBMjXJsGZ])
]
# Table: event
[
(event_id:TEXT, Primary Key, Examples: [rec0Si5cQ4rJRVzd6, rec0akZnLLpGUloLH, rec0dZPcWXF0QjNnE]),
(event_name:TEXT, Examples: [March Meeting]),
(event_date:TEXT, Examples: [2020-03-10T12:00:00, 2020-01-14T09:30:00, 2019-11-24T09:00:00]),
(type:TEXT, Examples: [Meeting, Election, Game]),
(notes:TEXT),
(location:TEXT, Examples: [MU 215]),
(status:TEXT, Examples: [Open, Planning, Closed])
]
【Foreign keys】
budget.link_to_event=event.event_id
member.link_to_major=major.major_id
member.zip=zip_code.zip_code
income.link_to_member=member.member_id
attendance.link_to_event=event.event_id
attendance.link_to_member=member.member_id
expense.link_to_budget=budget.budget_id
expense.link_to_member=member.member_id

    【Question】
    What are the zip codes that have post office boxes in the country of the country of San Juan Municipio whose state is Puerto Rico? zip codes that have post office boxes refers to type = 'PO Box'

    【Evidence】
    zip codes that have post office boxes refers to type = 'PO Box'

    Please read and understand the database schema carefully, and generate an executable SQL based on the user's question and evidence. 

SQL: SELECT zip_code FROM zip_code WHERE type = 'PO Box' AND county = 'San Juan Municipio' AND state = 'Puerto Rico'