Relational Database Terms and Definitions

Relational Database Terms and Definitions

1. Key: it is an important concept in a relational model. It is used to identify one or more columns of a row in a relational model.

2. Candidate Key: it is an attribute set that uniquely identifies a row in a table and does not contain any redundant attributes. That is, in the same table, A combination of more than one column may uniquely identify a row of data. The combination of any of these columns is the candidate keyword. 3. primary key ): it is a candidate keyword selected and used as the unique identifier of a table row. A table has only one primary key, which is also called a primary key. 4. common key ): in relational databases, links are expressed by compatible or identical attributes or attribute groups. If the two links have compatible or identical attributes or attribute groups, this attribute or attribute group is called the Public Keywords of these two relationships; 5. Foreign keywords (foreign key ): if a public keyword is a primary keyword in a link, this public keyword is called an external keyword of another link. It can be seen that the external keyword represents the relationship between two relations, and the external keyword is also called the foreign key; 6. Database relationship diagram: the relational object in the database is used to describe the correspondence between tables in the database. In the field of database technology, relational graph is also called E-R graph, ERD graph, ear graph and so on. 7. Table: similar to a commonly used table, a column is composed of rows and columns. A column is composed of similar information. A row of data is called a record. Each table usually has a primary key. 8. Index: The index is created based on the specified database table column. It provides a fast way to access data and can monitor the table data, make the data in the column to which the index points do not repeat; 9. View: The view looks like a table and has a group of named columns and data items, but it is actually a virtual table, it does not actually exist in the database. A view is generated by querying database tables. It limits the data that you can view and modify. 10. Chart: it is actually the relationship between database tables. You can use it to edit the relationship between tables. 11. Default Value: When a column is created or data is inserted in a table, a pre-set value is assigned to a column or column data item without a specific value. 12. Type: includes the system data type, user-defined data type, XML Schema set, and other object types. 13. Rule: it is a command that limits data information in database tables and limits columns in tables. 14. Trigger: it is a user-defined SQL transaction command set. When a table is inserted, changed, or deleted, these commands are automatically executed. 15. Stored Procedure: A stored procedure is a set of SQL statements that are aggregated to complete specific functions. It is compiled and stored in the database for users to call. Program 16. entity: an object is a data object. It can be a specific or abstract object. 17. attribute: it is a feature of an object. 18. identifier: entity instances all have identifiers, which are used to specify and distinguish different entities; 19. Field: The value range of the column data in the table;