relational-database

问题 as stated in the docs the current hasManyThrough can be used when u have something like country > users > posts which result in something like Country::whereName('xx')->posts; which is great but what if i have more than that like country > cities > users > posts or even country > cities > towns > users > posts how would you then implement something like that so you can write the same as above Country::whereName('xx')->posts; or Town::whereName('xx')->posts; 回答1: I created a HasManyThrough

问题 as stated in the docs the current hasManyThrough can be used when u have something like country > users > posts which result in something like Country::whereName('xx')->posts; which is great but what if i have more than that like country > cities > users > posts or even country > cities > towns > users > posts how would you then implement something like that so you can write the same as above Country::whereName('xx')->posts; or Town::whereName('xx')->posts; 回答1: I created a HasManyThrough

问题 as stated in the docs the current hasManyThrough can be used when u have something like country > users > posts which result in something like Country::whereName('xx')->posts; which is great but what if i have more than that like country > cities > users > posts or even country > cities > towns > users > posts how would you then implement something like that so you can write the same as above Country::whereName('xx')->posts; or Town::whereName('xx')->posts; 回答1: I created a HasManyThrough

来源： https://stackoverflow.com/questions/15370394/are-these-two-relations-compatible-for-a-union-operation

来源： https://stackoverflow.com/questions/15370394/are-these-two-relations-compatible-for-a-union-operation

问题 i am a student just starting out with python, and i was tasked with creating a relational database management system. I think i came pretty far, but i seem to have hit a wall. This is my code: import csv import sqlite3 conn = sqlite3.connect('unfccc.db') c = conn.cursor() c.execute('''CREATE TABLE unfccc ( Country TEXT, CodeCountryFormat TEXT, NamePollutant TEXT, NameYearSector TEXT, NameParent TEXT, Sector TEXT, CodeSector TEXT, CNUEDSPD TEXT )''') def insert_row(Country, CodeCountryFormat,

问题 i am a student just starting out with python, and i was tasked with creating a relational database management system. I think i came pretty far, but i seem to have hit a wall. This is my code: import csv import sqlite3 conn = sqlite3.connect('unfccc.db') c = conn.cursor() c.execute('''CREATE TABLE unfccc ( Country TEXT, CodeCountryFormat TEXT, NamePollutant TEXT, NameYearSector TEXT, NameParent TEXT, Sector TEXT, CodeSector TEXT, CNUEDSPD TEXT )''') def insert_row(Country, CodeCountryFormat,

问题 Some while ago, I've been reading through the book SQL and Relational Theory by C. J. Date. The author is well-known for criticising SQL's three-valued logic (3VL). 1) The author makes some strong points about why 3VL should be avoided in SQL, however he doesn't outline how a database model would look like if nullable columns weren't allowed . I've thought on this for a bit and have come up with the following solutions. If I missed other design options, I would like to hear about them! 1)

问题 I am trying to understand solution on one exercise that translates ER model to functional dependencies. As you can see above, we only have relation names and nothing else besides that, and by solution, they somehow come up to conclusion that mother, daughter → father father, daughter → mother mother, son → father father, son → mother And that moreover we can infer additional f dependencies to represent real world more accurately: mother, son → father father, son → mother What I don't

问题 Address ( addressID , houseNumber, postcode, roadName, city, county) Reservation ( reservationID , roomNo, leadGuestID, guest2ID, guest3ID , arrivalDate, departureDate, addressID , amountOutstanding) Guest ( guestID , firstName, lastName, adultFlag, telephoneNo, addressID , emailAddress) Room ( roomNo , roomTypeName ) RoomType ( roomTypeName , floor, basePrice, extraAdultPrice, extraChildPrice) The above schema is supposed to be normalised 4NF. But I cannot see how leadGuestID, guest2ID &