Database-related knowledge

1, the database is a structured data set;

2, the Data Environment is the object, the relation is the object in the data environment;

3. In a structured approach, data flow diagrams are used (DFD) the software development phase as a description tool is: Demand Analysis

4, in the software life cycle, can accurately determine what the software system must do and what must have the function of the stage is: demand Analysis

5. in the table structure, the widths of logical, date, and Memo fields are fixed to: 1 , 8 , 4

6. the three-level mode of the database system is: concept level mode, internal level mode and external level mode respectively.

7, relational model data manipulation is based on the relationship of data manipulation, generally have to query , add, delete and modify four operations.

8, the function value of the following function is the character type is ___B___.

A,DATE () B,time () C,year () D,DATETIME ()

9, the index is similar to the book directory, mainly used to improve query efficiency, that is, by the condition of the query, the first query index, and then through the index to find the relevant data, the index is equivalent to a keyword, assigned to a different file, or the structure of different locations in the file;

Indexing reduces the efficiency of data updates and causes an update of the index structure when inserted, modified, and deleted.

10 . The cursor is used to locate the row of the result set. By judging the global variable @ @FETCH_STATUS You can tell if it's up to the end. Usually this variable does not equal 0 to indicate an error or to the last.

11. use an SQL statement to find out the names of students who have more than one class per course  

name Kecheng score
Zhang San Chinese bayi
Zhang San Mathematics
John Doe language
John Doe math
Harry Chinese bayi
Harry Math
Harry English

Answer : SELECT DISTINCT name

from score   

where name not in (select distinct name from score where s Core<=80)

12.

Database-related knowledge