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Constants (Transact-SQL)

  • Artykuł

A constant, also known as a literal or a scalar value, is a symbol that represents a specific data value. The format of a constant depends on the data type of the value it represents.

  • Character string constants
    Character string constants are enclosed in single quotation marks and include alphanumeric characters (a-z, A-Z, and 0-9) and special characters, such as exclamation point (!), at sign (@), and number sign (#). Character string constants are assigned the default collation of the current database, unless the COLLATE clause is used to specify a collation. Character strings typed by users are evaluated through the code page of the computer and are translated to the database default code page if it is required.

    If the QUOTED_IDENTIFIER option has been set OFF for a connection, character strings can also be enclosed in double quotation marks, but the Microsoft SQL Server Native Client Provider and ODBC driver automatically use SET QUOTED_IDENTIFIER ON. We recommend using single quotation marks.

    If a character string enclosed in single quotation marks contains an embedded quotation mark, represent the embedded single quotation mark with two single quotation marks. This is not required in strings embedded in double quotation marks.

    The following are examples of character strings:

    'Cincinnati'
'O''Brien'
'Process X is 50% complete.'
'The level for job_id: %d should be between %d and %d.'
"O'Brien"

    Empty strings are represented as two single quotation marks with nothing in between. In 6.x compatibility mode, an empty string is treated as a single space.

    Character string constants support enhanced collations.

    [!UWAGA]

    Character constants greater than 8000 bytes are typed as varchar(max) data.

  • Unicode strings
    Unicode strings have a format similar to character strings but are preceded by an N identifier (N stands for National Language in the SQL-92 standard). The N prefix must be uppercase. For example, 'Michél' is a character constant while N'Michél' is a Unicode constant. Unicode constants are interpreted as Unicode data, and are not evaluated by using a code page. Unicode constants do have a collation. This collation primarily controls comparisons and case sensitivity. Unicode constants are assigned the default collation of the current database, unless the COLLATE clause is used to specify a collation. Unicode data is stored by using 2 bytes per character instead of 1 byte per character for character data. For more information, see Collation and Unicode Support.

    Unicode string constants support enhanced collations.

    [!UWAGA]

    Unicode constants greater than 8000 bytes are typed as nvarchar(max) data.

  • Binary constants
    Binary constants have the prefix 0x and are a string of hexadecimal numbers. They are not enclosed in quotation marks.

    The following are examples of binary strings are:

    0xAE
0x12Ef
0x69048AEFDD010E
0x  (empty binary string)

    [!UWAGA]

    Binary constants greater than 8000 bytes are typed as varbinary(max) data.

  • bit constants
    bit constants are represented by the numbers 0 or 1, and are not enclosed in quotation marks. If a number larger than one is used, it is converted to one.

  • datetime constants
    datetime constants are represented by using character date values in specific formats, enclosed in single quotation marks.

    The following are examples of datetime constants:

    'December 5, 1985'
'5 December, 1985'
'851205'
'12/5/98'

    Examples of time constants are:

    '14:30:24'
'04:24 PM'

  • integer constants
    integer constants are represented by a string of numbers that are not enclosed in quotation marks and do not contain decimal points. integer constants must be whole numbers; they cannot contain decimals.

    The following are examples of integer constants:

    1894
2

  • decimal constants
    decimal constants are represented by a string of numbers that are not enclosed in quotation marks and contain a decimal point.

    The following are examples of decimal constants:

    1894.1204
2.0

  • float and real constants
    float and real constants are represented by using scientific notation.

    The following are examples of float or real values:

    101.5E5
0.5E-2

  • money constants
    money constants are represented as string of numbers with an optional decimal point and an optional currency symbol as a prefix. money constantsare not enclosed in quotation marks.

    SQL Server does not enforce any kind of grouping rules such as inserting a comma (,) every three digits in strings that represent money.

    [!UWAGA]

    Commas are ignored anywhere in the specified money literal.

    The following are examples of money constants:

    $12
$542023.14

  • uniqueidentifier constants
    uniqueidentifier constants are a string representing a GUID. They can be specified in either a character or binary string format.

    The following examples both specify the same GUID:

    '6F9619FF-8B86-D011-B42D-00C04FC964FF'
0xff19966f868b11d0b42d00c04fc964ff

Specifying Negative and Positive Numbers

To indicate whether a number is positive or negative, apply the + or - unary operators to a numeric constant. This creates a numeric expression that represents the signed numeric value. Numeric constants use positive when the + or - unary operators are not applied.

  • Signed integer expressions:

    +145345234
-2147483648

  • Signed decimal expressions:

    +145345234.2234
-2147483648.10

  • Signed float expressions:

    +123E-3
-12E5

  • Signed money expressions:

    -$45.56
+$423456.99

Enhanced Collations

SQL Server supports character and Unicode string constants that support enhanced collations. For more information, see the COLLATE (Transact-SQL) clause.

Zobacz także

Odwołanie

Data Types (Transact-SQL)

Expressions (Transact-SQL)

Operators (Transact-SQL)