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Editor to share with you how Python uses txt files to add, delete, modify and check Mysql. I believe most people don't know much about it, so share this article for your reference. I hope you will get a lot after reading this article. Let's learn about it together.

1. Relational database 1. Data model

There are three types of relationships between entities:

1 *) one-to-one model

One to one (one-to-one)

The relational model uses two-dimensional tables to represent data and data connections, which is the most widely used data model. At present, all kinds of commonly used databases, such as Microsoft SQL Server, Microsoft Access, Microsoft FoxPro, Oracle, MySQL, SQLite and so on, belong to the relational model database management system.

2 *) one-to-many model

One to many (one-to-many)

The hierarchical model uses a tree structure to represent the relationship between data. the nodes of the tree are called records, and there is only a simple hierarchical relationship between records. One and only one node does not have a parent node, which is called the root node; the other nodes have one and only one parent node.

3 *) many-to-many model

Many to many (many-to-many)

You can have any number of nodes without a parent. A node allows multiple parent nodes. There can be two or more connections between two nodes.

two。 Face object model

1 *) object model concept

Object-oriented model is a kind of data model developed on the basis of object-oriented technology. It uses object-oriented method to design database.

2 *) characteristics of object model

The database of the object-oriented model stores objects in units of objects, each object contains the properties and methods of the object, and has the characteristics of class and inheritance.

Second, understand the concept and characteristics of relational database

The concept and characteristics of Relational Database

1. Basic concept

I *) relationship

The relationship between data and data is called a relationship.

Ii*) 2D table

Relational databases use two-dimensional tables to represent and store relationships, and a relationship is a two-dimensional table. The rows in the table are called records and the columns are called fields. A database can contain multiple tables

Iii*) records and fields

A row in a table is called a record. The data items in the columns in the table are called fields. A field is also called a property or column. Each record can contain multiple fields, and different records contain the same field (with different values for the field). For example, each record in the user table contains fields such as user name, login password, and so on.

A relational database does not allow duplicate records in a table.

VI*) keyword

Fields or combinations of fields that can uniquely identify a record are called keywords. A table can have multiple keywords, in which the keyword used to identify the record is called the primary keyword, and the other keywords can be called candidate keywords. Only one primary keyword is allowed for a table. For example, the user name in the user table can be defined as the primary keyword, which is not allowed to be repeated when adding records.

VII*) external keyword

If a field or combination of fields in one table is the primary key of another table, such a field or combination of fields is called an external key.

two。 Basic characteristics

The table in the relational database is a two-dimensional table, and the fields in the table must be inseparable, that is, tables in the table are not allowed.

Duplicate records are not allowed in the same table.

Duplicate fields are not allowed in the same record.

The order of records in the table does not affect the nature of the data, and the order of records can be exchanged.

The order of the fields in the record does not affect the data, and the order of the fields can be exchanged.

Third, commonly used field data types

Data table

Fourth, call the contents of the file TXT into the program in spyder

First step, first we need to write the contents of the file into spyder

When our file is successfully written into spyder, we can write a program!

The second step is to write menu programs

1. Make the home page menu

Def query_record (): print ('query student record') def modify_record (): print ('modify student record') def delete_record (): print ('delete student record') def add_record (): print ('add student record') def exit_record (): print ('exit the system') def login (): while True: Print ('main menu') print ('='* 2) print ('1. Query record') print ('2. Modify record') print ('3. Delete record') print ('4. Add record') print ('5. Exit the system') print ('='* 2) mc2 = int (input ('enter menu number:') if mc2 = = 1: query_record () elif mc2 = = 2: modify_record () Elif mc2 = = 3: delete_record () elif mc2 = = 4: add_record () elif mc2 = = 5: exit_record () else: break

When we finish writing the menu program, we can write the corresponding program for the menu program.

Write the corresponding program menu, such as the program after entering the query record menu.

two。 Make program menu

While True: print ('='* 2) print ('1. Query student record') print ('2. Modify student record') print ('3. Delete student record') print ('4. Add student record') print ('5. Exit system') print ('='* 2)

When we are finished, the overall architecture is in place, so that the code corresponding to each menu number can be implemented step by step!

First of all, write a program to query the student number.

3. Write a program to query the student number.

Mc1 = int (input ('Please enter menu number:') if mc1 = = 1: id=input ("Please enter the student number you want to query:") for student in students: found=False if (student [0] = = id): found=True print ("Congratulations on successful record query!") Print () for i in range (len (student)): print (student [I], end= "") print () break if not found: print ("the student whose name is {} cannot be found!" .format (id))

After querying the student number you want to modify, enter the revised new student number

4. Write a program to modify the student number

Elif mc1==2: id=input ("Please enter the student number you want to modify:") for student in students: found=False if (student [0] = = id): found=True student=list (student) Student [7] = int (input ("enter a new phone number:") student [3] = int (input ("enter a new age:") print ("Congratulations on successful record modification!") For i in range (len (student)): print (student [I], end= "") print () break if not found: print ("the student whose name is {} cannot be found!" .format (id))

After the query record program is compiled, you can modify the record program.

5. Write the program of student number

Elif mc1==2: id=input ("Please enter the student number you want to modify:") for student in students: found=False if (student [0] = = id): found=True student=list (student) Student [7] = int (input ("enter a new phone number:") student [3] = int (input ("enter a new age:") print ("Congratulations on successful record modification!") For i in range (len (student)): print (student [I], end= "") print () break if not found: print ("the student whose name is {} cannot be found!" .format (id))

After modifying the record program, you can write the delete record program.

6. Write a program to delete student records

Elif mc1==3: id=input ("Please enter the student ID you want to delete:") found=False for student in students: if (student [0] = = id): found=True students.remove (student) print ("Congratulations on successful record deletion!") Print () break if not found: print ("classmate whose name is {} not found!" .format (id)) else: for student in students: for i in range (len (student)): print (student [I] End= "") print ()

After the deletion record program is finished, you can add the record program to write!

7. Write a program to increase student records

The third step is to exit the system.

The above is all the contents of this article "how to add, delete, modify and query Python using txt files". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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