char and varchar (Transact-SQL)
Character data types that are either fixed-size, char, or variable-size, varchar. Starting with SQL Server 2019 (15.x), when a UTF-8 enabled collation is used, these data types store the full range of Unicode character data and use the UTF-8 character encoding. If a non-UTF-8 collation is specified, then these data types store only a subset of characters supported by the corresponding code page of that collation.
char [ ( n ) ] Fixed-size string data. n defines the string size in bytes and must be a value from 1 through 8,000. For single-byte encoding character sets such as Latin, the storage size is n bytes and the number of characters that can be stored is also n. For multibyte encoding character sets, the storage size is still n bytes but the number of characters that can be stored may be smaller than n. The ISO synonym for char is character. For more information on character sets, see Single-Byte and Multibyte Character Sets.
varchar [ ( n | max ) ] Variable-size string data. Use n to define the string size in bytes and can be a value from 1 through 8,000 or use max to indicate a column constraint size up to a maximum storage of 2^31-1 bytes (2 GB). For single-byte encoding character sets such as Latin, the storage size is n bytes + 2 bytes and the number of characters that can be stored is also n. For multi-byte encoding character sets, the storage size is still n bytes + 2 bytes but the number of characters that can be stored may be smaller than n. The ISO synonyms for varchar are charvarying or charactervarying. For more information on character sets, see Single-Byte and Multibyte Character Sets.
A common misconception is to think that CHAR(n) and VARCHAR(n), the n defines the number of characters. But in CHAR(n) and VARCHAR(n) the n defines the string length in bytes (0-8,000). n never defines numbers of characters that can be stored. This is similar to the definition of NCHAR(n) and NVARCHAR(n). The misconception happens because when using single-byte encoding, the storage size of CHAR and VARCHAR is n bytes and the number of characters is also n. However, for multi-byte encoding such as UTF-8, higher Unicode ranges (128-1,114,111) result in one character using two or more bytes. For example, in a column defined as CHAR(10), the Database Engine can store 10 characters that use single-byte encoding (Unicode range 0-127), but less than 10 characters when using multi-byte encoding (Unicode range 128-1,114,111). For more information about Unicode storage and character ranges, see Storage differences between UTF-8 and UTF-16.
When n isn't specified in a data definition or variable declaration statement, the default length is 1. If n isn't specified when using the CAST and CONVERT functions, the default length is 30.
Objects that use char or varchar are assigned the default collation of the database, unless a specific collation is assigned using the COLLATE clause. The collation controls the code page that is used to store the character data.
Multibyte encodings in SQL Server include:
- Double-byte character sets (DBCS) for some East Asian languages using code pages 936 and 950 (Chinese), 932 (Japanese), or 949 (Korean).
- UTF-8 with code page 65001. Applies to: SQL Server (Starting with SQL Server 2019 (15.x)))
If you have sites that support multiple languages:
- Starting with SQL Server 2019 (15.x), consider using a UTF-8 enabled collation to support Unicode and minimize character conversion issues.
- If using a lower version of the SQL Server Database Engine, consider using the Unicode nchar or nvarchar data types to minimize character conversion issues.
If you use char or varchar, we recommend to:
- Use char when the sizes of the column data entries are consistent.
- Use varchar when the sizes of the column data entries vary considerably.
- Use varchar(max) when the sizes of the column data entries vary considerably, and the string length might exceed 8,000 bytes.
If SET ANSI_PADDING is OFF when either CREATE TABLE or ALTER TABLE is executed, a char column that is defined as NULL is handled as varchar.
Each non-null varchar(max) or nvarchar(max) column requires 24 bytes of additional fixed allocation which counts against the 8,060 byte row limit during a sort operation. This can create an implicit limit to the number of non-null varchar(max) or nvarchar(max) columns that can be created in a table. No special error is provided when the table is created (beyond the usual warning that the maximum row size exceeds the allowed maximum of 8,060 bytes) or at the time of data insertion. This large row size can cause errors (such as error 512) during some normal operations, such as a clustered index key update, or sorts of the full column set, which will only occur while performing an operation.
Converting Character Data
When character expressions are converted to a character data type of a different size, values that are too long for the new data type are truncated. The uniqueidentifier type is considered a character type for the purposes of conversion from a character expression, and so is subject to the truncation rules for converting to a character type. See the Examples section that follows.
When a character expression is converted to a character expression of a different data type or size, such as from char(5) to varchar(5), or char(20) to char(15), the collation of the input value is assigned to the converted value. If a noncharacter expression is converted to a character data type, the default collation of the current database is assigned to the converted value. In either case, you can assign a specific collation by using the COLLATE clause.
Code page translations are supported for char and varchar data types, but not for text data type. As with earlier versions of SQL Server, data loss during code page translations isn't reported.
Character expressions that are being converted to an approximate numeric data type can include optional exponential notation. This notation is a lowercase e or uppercase E followed by an optional plus (+) or minus (-) sign and then a number.
Character expressions that are being converted to an exact numeric data type must consist of digits, a decimal point, and an optional plus (+) or minus (-). Leading blanks are ignored. Comma separators, such as the thousands separator in 123,456.00, aren't allowed in the string.
Character expressions being converted to money or smallmoney data types can also include an optional decimal point and dollar sign ($). Comma separators, as in $123,456.00, are allowed.
When an empty string get converted to an int, its value becomes
0. When an empty string gets converted to a date, its value becomes the default value for date - which is
A. Showing the default value of n when used in variable declaration
The following example shows the default value of n is 1 for the
varchar data types when they are used in variable declaration.
DECLARE @myVariable AS VARCHAR = 'abc'; DECLARE @myNextVariable AS CHAR = 'abc'; --The following returns 1 SELECT DATALENGTH(@myVariable), DATALENGTH(@myNextVariable); GO
B. Showing the default value of n when varchar is used with CAST and CONVERT
The following example shows that the default value of n is 30 when the
varchar data types are used with the
DECLARE @myVariable AS VARCHAR(40); SET @myVariable = 'This string is longer than thirty characters'; SELECT CAST(@myVariable AS VARCHAR); SELECT DATALENGTH(CAST(@myVariable AS VARCHAR)) AS 'VarcharDefaultLength'; SELECT CONVERT(CHAR, @myVariable); SELECT DATALENGTH(CONVERT(CHAR, @myVariable)) AS 'VarcharDefaultLength';
C. Converting Data for Display Purposes
The following example converts two columns to character types and applies a style that applies a specific format to the displayed data. A money type is converted to character data and style 1 is applied, which displays the values with commas every three digits to the left of the decimal point, and two digits to the right of the decimal point. A datetime type is converted to character data and style 3 is applied, which displays the data in the format dd/mm/yy. In the WHERE clause, a money type is cast to a character type to perform a string comparison operation.
USE AdventureWorks2012; GO SELECT BusinessEntityID, SalesYTD, CONVERT (VARCHAR(12),SalesYTD,1) AS MoneyDisplayStyle1, GETDATE() AS CurrentDate, CONVERT(VARCHAR(12), GETDATE(), 3) AS DateDisplayStyle3 FROM Sales.SalesPerson WHERE CAST(SalesYTD AS VARCHAR(20) ) LIKE '1%';
Here is the result set.
BusinessEntityID SalesYTD DisplayFormat CurrentDate DisplayDateFormat ---------------- --------------------- ------------- ----------------------- ----------------- 278 1453719.4653 1,453,719.47 2011-05-07 14:29:01.193 07/05/11 280 1352577.1325 1,352,577.13 2011-05-07 14:29:01.193 07/05/11 283 1573012.9383 1,573,012.94 2011-05-07 14:29:01.193 07/05/11 284 1576562.1966 1,576,562.20 2011-05-07 14:29:01.193 07/05/11 285 172524.4512 172,524.45 2011-05-07 14:29:01.193 07/05/11 286 1421810.9242 1,421,810.92 2011-05-07 14:29:01.193 07/05/11 288 1827066.7118 1,827,066.71 2011-05-07 14:29:01.193 07/05/11
D. Converting Uniqueidentifer Data
The following example converts a
uniqueidentifier value to a
char data type.
DECLARE @myid uniqueidentifier = NEWID(); SELECT CONVERT(CHAR(255), @myid) AS 'char';
The following example demonstrates the truncation of data when the value is too long for the data type being converted to. Because the uniqueidentifier type is limited to 36 characters, the characters that exceed that length are truncated.
DECLARE @ID NVARCHAR(max) = N'0E984725-C51C-4BF4-9960-E1C80E27ABA0wrong'; SELECT @ID, CONVERT(uniqueidentifier, @ID) AS TruncatedValue;
Here is the result set.
String TruncatedValue -------------------------------------------- ------------------------------------ 0E984725-C51C-4BF4-9960-E1C80E27ABA0wrong 0E984725-C51C-4BF4-9960-E1C80E27ABA0 (1 row(s) affected)