Chapter 2 Relational Database
1. Relations and related concepts:
Domain : A set of values with the same data type, such as {male, female} (the definition of a domain is a frequent visitor to multiple-choice questions)
The cardinality of the domain: the number of different values allowed in a domain
Cartesian product: D1XD2X……XDn
Example: D1={张,王,李} D2={cs,math} D3={T,S}
There are 3 2 2=12 combinations of
candidate codes : the value of a certain attribute group Can uniquely identify a tuple, but its subset cannot , then the attribute group is called the candidate code
main code : one of the candidate codes
Full code: candidate code = all attributes
Main attribute: the attribute of the candidate code is
not the main attribute/non-code Attribute: Not a candidate code
There are three types of relationships: basic relationships ( basic tables or base tables- actual tables ), query tables (tables corresponding to query results), and view tables ( virtual tables derived from basic tables or other view tables )
2. Relationship mode: description of the relationship R (U, D, DOM, F)
R: the name
of the relationship U: the set of attribute names that make up the relationship
D: the domain from which the attributes in U come from
DOM: the set of mapping attributes to the domain
F: Data dependency collection between attributes
3. The relationship model is static and stable , while the relationship is dynamic and constantly changing over time
4. Relational database: The type of relational database is also called the relational data model, which is a description of the relational database.
The value of a relational database is a collection of relations corresponding to these relational patterns at a certain moment, which is generally called a relational database.
5. The storage structure of the relational model: table storage
6. Relational operations: query (selection, projection,
union , difference, Cartesian product, connection, division, intersection), insert, delete, modify the objects and results of operations are all sets
7. Relationship integrity:
(1) Entity integrity : If attribute A is the primary attribute of basic relationship R, then A cannot take a null value .
Note: The concept of outer code : Let F be one or a group of attributes of basic relation R, but not the code of relation R, and Ks is the main code of basic relation S. If F corresponds to Ks, then F is the outer code of R, and the basic relationship R is called the reference relationship, and the basic relationship S is the referenced relationship.
R(Kr,F,…)->S(Ks,…)
(2) Referential integrity: If the attribute F is the outer code of R, which corresponds to the main code Ks of the basic relationship S, then the value of each tuple in R on F must be: either a null value; or equal to The main code value of a tuple in S
(3) User-defined completeness: for example age[0~65]
Chapter 3 Structured Query Language SQL
Functions: data query, data manipulation, data definition, data control
1. SQL features:
(1) Comprehensive and unified
integration of data query, data manipulation, data definition, and data control functions, which can independently complete all activities in the DB life cycle
(2) Highly non-procedural
What to do (√) How Do understand the storage path
(3) Set-oriented operation mode
(4) Provide multiple usage methods with the same grammatical structure
(5) Simple language, easy to learn and use
2. SQL verb
data query: SELECT
data definition: CREATE, DROP, ALTER
data manipulation: INSERT, UPDATE, DELETE
data control: GRANT, REVOKE
