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1. Database three paradigms
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1NF: Atomicity, the column can not be divided
2NF:
a second first-dependent paradigm paradigm, the second paradigm must meet the first and second Paradigm ensure that the database table and each column associated primary key
3NF:
At basis paradigm one step further, the goal is to ensure that each column and is directly related to the primary key column, rather than indirectly (additional non-primary key column must be directly dependent on the primary key, can not rely on the presence of transfer).
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2. The four ACID properties of transaction management
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transaction atomicity (Atomicity) :
refers to a transaction either all executed or not executed, that is to say a transaction can not be executed only half stopped. For example, you withdraw money from a cash machine, the transaction can be divided into two steps: 1 draw card, 2 money. Impossible to draw a card, but the money did not come out. These two steps must be completed at the same time, or it does not complete.
Transactional consistency (Consistency) :
refers to the operation of the transaction does not change the consistency of data in the database. For example, the integrity constraint a + b = 10, a transaction changing a, then b should be changed.
Independence (Isolation) :
Independence transaction may be called barrier properties, refers to two or more interleaved state of affairs will not be executed. As this may result in inconsistent data.
Persistent (Durability Rev) :
Persistence refers to transactions after the transaction is successful, the transaction changes made to the database is stored in the persistent database, not for no reason rollback.