1. Introduction
In MySQL databases, varchar and text are common data types that are used to store text data. Although they can all be used to store strings, they have some differences in storage capacity, performance impact, queries, and indexes. This article will explore the definition, characteristics, storage methods and applicable scenarios of varchar and text to help you better understand and use these two data types.
2. Data Type Overview
Data types play an important role in a database and are used to define the type and format of data stored in columns. MySQL provides a variety of data types, including integers, floating point numbers, date/time, strings, etc. In this section, we will briefly introduce the role of data types and list some common MySQL data types.
3. varchar data type
Definition and Features
varchar is a variable-length string type used to store variable-length character data. Its definition includes a maximum length parameter that represents the maximum number of characters that the column can store.
Storage method
The storage method of varchar is related to its length. When storing varchar values, MySQL allocates enough storage space according to the actual data length. For example, if a varchar column has a maximum length of 50, but the actual stored string has only 10 characters, only 10 characters of storage space will be allocated.
Applicable scenarios
varchar is suitable for storing variable-length strings, such as usernames, addresses, etc. It provides the advantages of flexibility and storage space saving.
4. text data type
Definition and Features
text is a data type used to store large amounts of text data. It can store very long strings, the maximum length depends on the configuration of the database.
Storage method
Unlike varchar, data of type text always takes up enough storage space to accommodate its maximum length. No matter how long the text data is actually stored, it will take up enough storage space.
Applicable scenarios
text is suitable for storing large segments of text data, such as article content, logging, etc. It provides the ability to store large amounts of text data, but in some cases it may take up more storage space.
5. Differences and comparisons
Storage capacity
The storage capacity of a varchar is allocated according to the actual data length, and the text always takes up enough storage space to accommodate its maximum length.
Performance impact
Since varchar is fixed length, it may be faster than text when storing and retrieving. Data of type text requires additional processing and storage.
Query and index
varchar can use indexes for quick query, while text-type data cannot use indexes directly. If you need to query text, you can use full text indexing or other special search techniques.
The impact of storage engines
Different storage engines may handle varchar and text types differently. Some storage engines may have specific optimizations for the storage of varchar and text.
6. Sample code
Create a table
CREATE TABLE example (
id INT PRIMARY KEY,
name VARCHAR(50),
description TEXT
);
Insert data
INSERT INTO example (id, name, description) VALUES (1, 'John', 'This is a varchar example'); INSERT INTO example (id, name, description) VALUES (2, 'Jane', 'This is a text example');
Query data
SELECT * FROM example;
7. Things to note
Character sets and collation rules
When using varchar and text types, be careful to select the appropriate character set and collation rules to ensure the correctness and consistency of the data.
Optimization of storage space
If you need to store a large amount of text data, you can consider using the text type. However, it is important to note that the text type may take up more storage space, so storage requirements and performance requirements need to be considered when designing a database.
Data migration and compatibility
When migrating data or interacting with other systems, be careful about the compatibility of varchar and text types. Different database systems may have different implementation methods and limitations.
8. Summary
In this article, we explore the difference between varchar and text in MySQL. varchar is suitable for storing variable-length strings, while text is suitable for storing large amounts of text data. We compared their differences in storage capacity, performance impact, query and indexing, and storage engines. Choosing the right data type is very important for database design and performance optimization.
Attached:
Attachment: Application scenarios of char, varchar, text
When storing strings, you can use char, varchar or text types. So what about the specific usage scenario?
1. The char length is fixed, that is, each piece of data occupies equal bytes of space; it is suitable for use in ID number, mobile phone number, etc.
2. Varchar variable length, can set the maximum length; suitable for use in properties with variable length.
3. Text does not set length. When you do not know the maximum length of the attribute, text is suitable.
According to the query speed: char is the fastest, varchar is the second, and text is the slowest.
1. char: n in char(n) represents the number of characters, with a maximum length of 255 characters; if it is utf8 encoding method, then the char type accounts for 255 * 3 bytes. (UTF8's next character takes up 1 to 3 bytes)
2. varchar: n in varchar(n) represents the number of characters, the maximum space is 65535 bytes, and the number of characters stored is related to the character set;
- n in varchar(n) before MySQL5.0.3 represents the number of bytes; n in varchar(n) after MySQL5.0.3 represents the number of characters;
- The actual range of varchar is 65532 or 65533, because the content header will occupy 1 or 2 bytes to save the length of the string; if the field default null (i.e. the default value is empty), the entire record needs 1 byte to save the default value null.
If it is utf8 encoding, then varchar can store up to 65532/3 = 21844 characters.
3. Text: Basically the same as varchar, theoretically, it can save up to 65,535 characters. In fact, the text takes up a maximum memory space of 65,535 bytes; considering the character encoding method, one character occupies multiple bytes, text cannot store so many characters; the difference from varchar is that text requires 2 bytes to record the total number of bytes in the field.
Since varchar query speed is faster, you don't need text when you can use varchar.
9. References
- MySQL official documentation: /doc/
- MySQL data type: /doc/refman/8.0/en/
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