Kinh Nghiệm Hướng dẫn What are the differences between character data type and string data type with example? Mới Nhất
Lê Minh Long đang tìm kiếm từ khóa What are the differences between character data type and string data type with example? được Cập Nhật vào lúc : 2022-11-04 06:06:04 . Với phương châm chia sẻ Thủ Thuật về trong nội dung bài viết một cách Chi Tiết Mới Nhất. Nếu sau khi Read Post vẫn ko hiểu thì hoàn toàn có thể lại phản hồi ở cuối bài để Mình lý giải và hướng dẫn lại nha.Character Data Types
Nội dung chính Show- Can I just use VARCHAR for everything?What’s the difference between CHAR and VARCHAR?When should I use CHAR instead of VARCHAR?Further ReadingWhat is character data type with example?What is the difference between char and string?What is a string data type example?What is difference between char and varchar with example?
Character data types are strings of characters. Upper and lower case alphabetic characters are accepted literally. There is one fixed-length character data type: char, and two variable-length character data types: varchar and long varchar.
The maximum length of a character column cannot exceed 32,000 bytes for a non-UTF-8 installation and 16,000 bytes for a UTF-8 installation.
Char Data Types
Fixed-length char strings can contain any printing or non-printing character, and the null character ('�'). Char strings are padded with blanks to the declared length.
Leading and embedded blanks are significant when comparing char strings. For example, the following char strings are considered different:
'A B C'
'ABC'
Length is not significant when comparing char strings; the shorter string is (logically) padded to the length of the longer. For example, the following char strings are considered equal:
'ABC'
'ABC '
Varchar Data Types
Varchar strings are variable-length strings. The varchar data type can contain any character, including non-printing characters and the ASCII null character ('�').
Except when comparing with char data, blanks are significant in the varchar data type. For example, the following two varchar strings are not considered equal:
'the store is closed'
and
'thestoreisclosed'
If the strings being compared are unequal in length, the shorter string is padded with trailing blanks until it equals the length of the longer string.
For example, consider the following two strings:
'abcd�01'
where:
'�01' represents one ASCII character (ControlA)
and
'abcd'
If they are compared as varchar data types, then
'abcd' > 'abcd�01'
because the blank character added to 'abcd' to make the strings the same length has a higher value than ControlA ('�40' is greater than '�01').
Long Varchar Data Types
The intrinsic Ingres DBMS longvarchar data type is supported in OpenROAD through the LongVarcharObject system class. For more information, see LongVcharObject Class.
Your database is made of data; data is defined by data types. Data types are so fundamental that they’re often overlooked, but here are a few very common questions, and their answers.
Can I just use VARCHAR for everything?
The short answer is: No.
Sure, VARCHAR is very flexible and will accept most kinds of data. But using VARCHAR for everything robs your database of critical functionality, data consistency, and performance.
Let’s take the
example of storing date data in a VARCHAR column. We’ve instantly lost functionality, because we can’t easily add, subtract, or compare our date data. If we use one of the date data types (e.g., DATETIME, SMALLDATE, etc.) then we have a host of system functions like DATEADD and DATEPART.
Another problem with storing date data in a VARCHAR is that we have no built-in format control. Our system will now readily accept all of the following as “valid” date data:
- February
1, 2010eFbruary 1, 2010Feb 1 2010Star date 002.1.2010.3042-1-20102-1-2010 3:03pm02012010020110February 31, 2010
We want to unify and enforce the date format in the database, so we can easily seek out date errors (like February 31) and compare date, for example: SELECT columns FROM table1 WHERE myDate > ‘1/1/2010’.
We run into the same issues no matter what non-string type we try to store in VARCHAR.
What’s the difference between CHAR and VARCHAR?
The short answer is: VARCHAR is variable length, while CHAR is fixed length.
CHAR is a fixed length string data type, so any remaining space in the field is padded with blanks. CHAR takes up 1 byte per character. So, a CHAR(100) field (or variable) takes up 100 bytes on disk, regardless of the string it holds.
VARCHAR is a variable length string data type, so it holds only the characters you assign to it. VARCHAR takes up 1 byte per character, + 2 bytes to hold length information. For example, if you set a VARCHAR(100) data type = ‘Jen’, then it would take up 3 bytes (for J, E, and N) plus 2 bytes, or 5 bytes in all.
You can see how the use of VARCHAR in most cases is preferred, to save space. Let’s take a look a script; it declares a CHAR and a VARCHAR variable, sets each equal to the string ‘SQL’, and then SELECTs each variable to display what is actually stored:
DECLARE @myChar CHAR(100) , @myVarchar VARCHAR(100)
SET @myChar = 'SQL'
SET @myVarchar = 'SQL'
SELECT '[BEGIN]' + @myChar + '[END]' AS CHAR_Data
SELECT '[BEGIN]' + @myVarchar + '[END]' AS VARCHAR_Data
Here is the result when you run the script:
Char_Data
[BEGIN]SQL[END]
Varchar_Data
[BEGIN]SQL[END]
This demo just makes a nice visual of all the extra padding (and space wasted) CHAR uses.
When should I use CHAR instead of VARCHAR?
The short answer is: Almost never.
VARCHAR only costs two “extra” bytes, when compared to CHAR. It’s only in rare cases where using CHAR will actually save you space and effort. Examples of those cases:
- CHAR(2) for state abbreviation. If your business rules say that the State column will ALWAYS be two characters long, then use CHAR(2).Fixed length product codes (e.g., CHAR(8) for product codes like ‘004-3228’). Just like the state; if you have a field, like product code, that is ALWAYS (now and forevermore) a set length, then CHAR is preferred.A single letter
string. For example, we should use CHAR(1) for a middle initial column.
Your developers, users, and your database will be much happier if you use proper data types.
Further Reading
- Microsoft: Char and VarcharMicrosoft: CAST and CONVERTMicrosoft:
Data Types
What is character data type with example?
The CHAR data type stores character data in a fixed-length field. Data can be a string of single-byte or multibyte letters, numbers, and other characters that are supported by the code set of your database locale.What is the difference between char and string?
char is a primitive data type whereas String is a class in java. char represents a single character whereas String can have zero or more characters. So String is an array of chars. We define char in java program using single quote (') whereas we can define String in Java using double quotes (").What is a string data type example?
The string data types are CHAR , VARCHAR , BINARY , VARBINARY , BLOB , TEXT , ENUM , and SET .What is difference between char and varchar with example?
The short answer is: VARCHAR is variable length, while CHAR is fixed length. CHAR is a fixed length string data type, so any remaining space in the field is padded with blanks. CHAR takes up 1 byte per character. So, a CHAR(100) field (or variable) takes up 100 bytes on disk, regardless of the string it holds. Tải thêm tài liệu liên quan đến nội dung bài viết What are the differences between character data type and string data type with example?