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Specify Field Length by Using bcp (SQL Server)

  • Článek

The field length indicates the maximum number of characters that are required to represent data in character format. The field length is already known if the data is stored in the native format; for example, the int data type takes 4 bytes. If you have indicated 0 for the prefix length, the bcp command prompts you for field length, the default field lengths, and the impact of field-length on data storage in data files that contain char data.

The bcp Prompt for Field Length

If an interactive bcp command contains the in or out option without either the format file switch (-f) or a data-format switch (-n, -c, -w, or -N), the command prompts for the field length of each data field, as follows:

Enter length of field <field_name> [<default>]:

For an example that shows this prompt in context, see Specify Data Formats for Compatibility when Using bcp (SQL Server).

Note

After you interactively specify all of the fields in a bcp command, the command prompts you save your responses for each field in a non-XML format file. For more information on non-XML format files, see Non-XML Format Files (SQL Server).

Whether a bcp command prompts for field length depends on several factors, as follows:

  • When you copy data types that are not of fixed length and you specify a prefix length of 0, bcp prompts for a field length.

  • When converting noncharacter data to character data, bcp suggests a default field length large enough to store the data.

  • If the file storage type is noncharacter, the bcp command does not prompt for a field length. The data is stored in the Microsoft SQL Server native data representation (native format).

Using Default Field Lengths

Generally, Microsoft recommends that you accept the bcp-suggested default values for the field length. When a character mode data file is created, using the default field length ensures that data is not truncated and that numeric overflow errors do not occur.

If you specify a field length that is incorrect, problems can occur. For instance, if you copy numeric data and you specify a field length that is too short for the data, the bcp utility prints an overflow message and does not copy the data. Also, if you export datetime data and specify a field length of less than 26 bytes for the character string, the bcp utility truncates the data without an error message.

Important

When the default size option is used, SQL Server expects to read an entire string. In some situations, use of a default field length can lead to an "unexpected end of file" error. Typically, this error occurs with the money and datetime data types when only part of the expected field occurs in the data file; for example, when a datetime value of mm/dd/yy is specified without the time component and is, therefore, shorter than the expected 24 character length of a datetime value in char format. To avoid this type of error, use field terminators or fixed-length data fields, or change the default field length by specifying another value.

Default Field Lengths for Character File Storage

The following table lists the default field lengths for data to be stored as a character-file storage type. Nullable data is the same length as nonnull data.

Data type Default length (characters)
char Length defined for the column
varchar Length defined for the column
nchar Twice the length defined for the column
nvarchar Twice the length defined for the column
Text 0
ntext 0
bit 1
binary Twice the length defined for the column + 1
varbinary Twice the length defined for the column + 1
image 0
datetime 24
smalldatetime 24
float 30
real 30
int 12
bigint 19
smallint 7
tinyint 5
money 30
smallmoney 30
decimal 41*
numeric 41*
uniqueidentifier 37
timestamp 17
varchar(max) 0
varbinary(max) 0
nvarchar(max) 0
UDT Length of the user-defined term (UDT) column
XML 0

*For more information about the decimal and numeric data types, see decimal and numeric (Transact-SQL).

Note

A column of type tinyint can have values from 0 through 255; the maximum number of characters that are needed to represent any number in that range is three (representing values 100 through 255).

Default Field Lengths for Native File Storage

The following table lists the default field lengths for data to be stored as native file storage type. Nullable data is the same length as nonnull data, and character data is always stored in character format.

Data type Default length (characters)
bit 1
binary Length defined for the column
varbinary Length defined for the column
image 0
datetime 8
smalldatetime 4
float 8
real 4
int 4
bigint 8
smallint 2
tinyint 1
money 8
smallmoney 4
decimal 1 *
numeric 1 *
uniqueidentifier 16
timestamp 8

1 For more information about the decimal and numeric data types, see decimal and numeric (Transact-SQL).

In all of the preceding cases, to create a data file for later reloading into SQL Server that keeps the storage space to a minimum, use a length prefix with the default file storage type and the default field length.

See Also

bcp Utility
Data Types (Transact-SQL)
Specify Field and Row Terminators (SQL Server)
Specify Prefix Length in Data Files by Using bcp (SQL Server)
Specify File Storage Type by Using bcp (SQL Server)
Keep Nulls or Use Default Values During Bulk Import (SQL Server)