Karteikarten
Normalisation
Karten in diesem Stapel (10)
- 1how to design a relational database? basicessentially you need to look at the database and look at the fields (columns)
decide which first field will result in repetition of data in following fields and data
make that a foreign key and build second table with that field as primary key - 2what is normalisationthe concept of gradually splitting tables in a database and arranging it from 1st through to 3rd normal form
- 3rules for first normal form1. all field names (column headings, titles) must be unique (avoid confusion)
2. values in field should be from same
domain (same type), split field if not into appropriate fields
3. there should only be a SINGLE value in each element of the field
4. records cant be completely identical
5. each table needs primary key - 4what is a composite key and when to use it.A composite key is a combination of two or more fields that uniquely identify a record
- 5what are the rules for second normal form?make sure data is already in 1NF
remove any partial dependencies are removed: Meaning, any one of the primary key (composite key) fields where other fields can be fetched using it
fix any Many to Many relationships formed - 6trick for splitting tablefind whatever field you feel you can use to infer another bit of information. E.g, classroom and teacher. from whatever classroom, you can guess or infer what the teacher will be
- 7how to fix a many to many relationshipassign a new table using a COMPOSITE Key made up of BOTH PRIMARY KEYS from the original tables.
place that new table in the middle as a linking table, linking the two other tables using two ONE TO MANY links - 8third normal form rules1. data must be in 2nd normal form
2. where not all fields are dependant on the key the whole key and nothing but the key"
3. remove any none primary key key dependencies - 9what are the definitions of the different normal forms?1st normal: a table where there are no repeating fields or attributes
2nd normal. A table that's, already in 1st normal and where there are no attributes that are dependant on any one of the composite key. no partial dependencies
3rd normal. a table that's in the 2nd normal and contains NO, NON-KEY DEPENDANCIES, meaning there are no keys that depend on any other non primary key - 10what to do if theres no specific id or primary keymake a composite key with 2 ideal fields
MAKE SURE TO LOOK AT RELATIONSHIP BETWEEN TABLE NAMES
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- Highers computing (semester 2) Karteikarten am Normalisation, erstellt von Daniel Nnajiuba am 12/03/2022.
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- Daniel Nnajiuba
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