Difference Between Byte and Char in Column Datatypes

Difference between BYTE and CHAR in column datatypes

Let us assume the database character set is UTF-8, which is the recommended setting in recent versions of Oracle. In this case, some characters take more than 1 byte to store in the database.

If you define the field as VARCHAR2(11 BYTE), Oracle can use up to 11 bytes for storage, but you may not actually be able to store 11 characters in the field, because some of them take more than one byte to store, e.g. non-English characters.

By defining the field as VARCHAR2(11 CHAR) you tell Oracle it can use enough space to store 11 characters, no matter how many bytes it takes to store each one. A single character may require up to 4 bytes.

Difference between varchar2(10), varchar2(10 byte) and varchar2(10 char)

VARCHAR2(10 byte) will support up to 10 bytes of data, which could be as few as two characters in a multi-byte character sets.

VARCHAR2(10 char) could support as much as 40 bytes of information and will support to up 10 characters of data.

Varchar2(10) uses the current value of NLS_LENGTH_SEMANTICS to determine the limit for the string.

incase of byte, then it's 10 bytes.

incase of char, then it's 10 characters.

In multibyte character sets these can be different! So if NLS_LENGTH_SEMANTICS = byte, you may only be able to store 5 characters in your varchar2.
So varchar2(10 char) is explicit. This can store up to 10 characters. Varchar2(10) is implicit. It may store 10 bytes or 10 characters, depending on the DB configuration.

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What is the major difference between Varchar2 and char

Simple example to show the difference:

SELECT 
    '"'||CAST('abc' AS VARCHAR2(10))||'"', 
    '"'||CAST('abc' AS CHAR(10))||'"' 
FROM dual;


'"'||CAST('ABC'ASVARCHAR2(10))||'"' '"'||CAST('ABC'ASCHAR(10))||'"'
----------------------------------- -------------------------------
"abc"                               "abc       "                   
1 row selected.

The CHAR is usefull for expressions where the length of charaters is always fix, e.g. postal code for US states, for example CA, NY, FL, TX

varchar2(n BYTE|CHAR) default - CHAR or BYTE

The default will be whatever your NLS_LENGTH_SEMANTICS parameter is set to. By default, that is BYTE to be consistent with older versions of Oracle where there was no option to use character length semantics. If you are defining your own schema and you are using a variable width character set (like AL32UTF8), I'd strongly recommend setting NLS_LENGTH_SEMANTICS to CHAR because you almost always intended to specify lengths in characters not in bytes.

What does it mean when the size of a VARCHAR2 in Oracle is declared as 1 byte?

You can declare columns/variables as varchar2(n CHAR) and varchar2(n byte).

n CHAR means the variable will hold n characters. In multi byte character sets you don't always know how many bytes you want to store, but you do want to garantee the storage of a certain amount of characters.

n bytes means simply the number of bytes you want to store.

varchar is deprecated. Do not use it.
What is the difference between varchar and varchar2?

What's the difference between VARCHAR and CHAR?

VARCHAR is variable-length.

CHAR is fixed length.

If your content is a fixed size, you'll get better performance with CHAR.

See the MySQL page on CHAR and VARCHAR Types for a detailed explanation (be sure to also read the comments).

WHAT is the meaning of Leading Length?

The CHAR() datatype pads the string with characters. So, for 'ORATABLE', it looks like:

'ORATABLE            '
 12345678901234567890

The "leading length" are two bytes at the beginning that specify the length of the string. Two bytes are needed because one byte is not enough. Two bytes allow lengths up to 65,535 units; one byte would only allow lengths up to 255.

The important point both CHAR() and VARCHAR2() use the same internal format, so there is little reason to sue CHAR(). Personally, I would only use it for fixed-length codes, such as ISO country codes or US social security numbers.

SQL: What is better a Bit or a char(1)

For SQL Server: up to 8 columns of type BIT can be stored inside a single byte, while each column of type CHAR(1) will take up one byte.

On the other hand: a BIT column can have two values (0 = false, 1 = true) or no value at all (NULL) - while a CHAR(1) can have any character value (much more possibilities)

So really, it comes down to:

• do you really need a true/false (yes/no) field? If so: use BIT
• do you need something with more than just two possible values - use CHAR(1)

I don't think it makes any significant difference, from a performance point of view - unless you have tens of thousands of columns. Then of course, using BIT which can store up to 8 columns in a single byte would be beneficial. But again: for your "normal" database case, where you have a few, a dozen of those columns, it really doesn't make a big difference. Pick the column type that suits your needs - don't over-worry about performance.....

What is difference between char and varchar

As you said varchar is variable-length and char is fixed. But the main difference is the byte it uses.

Example.

column: username
type: char(10)

if you have data on column username which is 'test', it will use 10 bytes. and it will have space.

'test______'

Hence the varchar column will only uses the byte you use. for 'test' it will only use 4 bytes. and your data will be

'test'

THanks.

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