Shulou(Shulou.com)06/01 Report--

Transaction (Transaction): organize multiple operations as a whole, either all or none at all

"Roll back", rollback

Whether a storage system supports transactions, test criteria:

ACID:

A: atomicity

C: consistency

I: isolation

D: persistence

Databases: data collection

Table: to meet the requirements of paradigm design, split a dataset into multiple

Constraints: constraint, restrictions to follow when inserting data into a data table

Primary key: a combination of one or more fields in which the data in the primary key must be different from the existing data; it cannot be empty.

Foreign key: data that can be inserted in a field in a table, depending on the data in the primary key of another table

Unique key: a combination of one or more fields in which the data in the unique key must be different from the existing data; it can be empty.

Checking constraints: depending on the requirements of the expression

Index: extract one or more fields from a table and organize them into a unique data structure.

Commonly used index types:

Tree type:

Hash:

Note: it helps to read the request, but not to write the request

Relational operation:

Select: pick out rows that meet the criteria

Projection: pick the columns that meet your needs

Join: associating multiple tables

Data abstraction:

Physical layer: determines the storage format of the data, that is, how to organize the data into physical files

Logic layer: describes what data DB stores and what relationships exist between the data

View layer: describing part of the data in DB

Classification of relational models:

Relation model

Entity-relation model

Object-based relational model

Semi-structured relation model

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