Specifying Data Formats for Compatibility by Using bcp
When you bulk export Microsoft SQL Server data for bulk import into another program, such as another database program, the default data formats (native, character, or Unicode) in the source table might be incompatible with the data layout expected by the other program. If an incompatibility exists, when you export the data, you must describe the data layout.
If you are unfamiliar with data formats for importing or exporting data, see Data Formats for Importing or Exporting Data.
The bcp command allows you to specify the structure of each field in a data file in terms of the following data-format attributes:
- File storage type
The file storage type describes how data is stored in the data file. Data can be exported to a data file as its database table type (native format), in its character representation (character format), or as any data type where implicit conversion is supported; for example, copying a smallint as an int. User-defined data types are exported as their base types. For more information, see Specifying File Storage Type by Using bcp.
- Prefix length
To provide the most compact file storage for the bulk export of data in native format to a data file, the bcp command precedes each field with one or more characters that indicates the length of the field. These characters are called length prefix characters. For more information, see Specifying Prefix Length in Data Files.
- Field length
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 more information, see Specifying Field Length by Using bcp.
- Field terminator
For character data fields, optional terminating characters allow you to mark the end of each field in a data file (using a field terminator) and the end of each row (using a row terminator). Terminating characters are one way to indicate to programs reading the data file where one field or row ends and another begins. For more information, see Specifying Field and Row Terminators.
Overview of the Field-Specific Prompts
If an interactive bcp command contains the in or out option but does not also contain either the format file switch (-f) or a data-format switch (-n, -c, -w, or -N), each column in the source or target table, the command prompts for each of the preceding attributes, in turn. In each prompt, the bcp command provides a default value based on the SQL Server data type of the table column. Accepting the default value for all of the prompts produces the same result as specifying native format (-n) on the command line. Each prompt displays a default value in brackets: [default]. Pressing ENTER accepts the displayed default. To specify a value other than the default, enter the new value at the prompt.
The following example uses the bcp command to bulk export data from the
HumanResources.myTeam table interactively to the
myTeam.txt file. Before you can run the example, you must create this table. For information about the table and how to create it, see Creating the HumanResources.myTeam Table.
The command specifies neither a format file nor a data type, causing bcp to prompt for data-format information. At the Microsoft Windows command prompt, enter:
bcp AdventureWorks.HumanResources.myTeam out myTeam.txt -T
For each column, bcp prompts for field-specific values. The following example shows the field-specific prompts for the
Name columns of the table, and suggests the default file storage type (the native format) for each column. The prefix lengths of the
Name column are 0 and 2, respectively. The user specifies a comma (
,) as the terminator of each field.
Enter the file storage type of field EmployeeID [smallint]:
Enter prefix-length of field EmployeeID :
Enter field terminator [none]:,
Enter the file storage type of field Name [nvarchar]:
Enter prefix length of field Name :
Enter field terminator [none]:,
Equivalent prompts (as needed) are displayed for each of the table columns in order.
Storing Field-by-Field Data in a Non-XML Format File
After all of the table columns are specified, the bcp command prompts you to optionally generate a non-XML format file that stores the field-by-field information just supplied (see the preceding example). If you choose to generate a format file, you can whenever you export data out of that table or import like-structured data into SQL Server.
You can use the format file to bulk import data from the data file into an instance of SQL Server or to bulk export data from the table, without needing to respecify the format. For more information, see Format Files for Importing or Exporting Data.
The following example creates a non-XML format file named
Do you want to save this format information in a file? [Y/n] y
Host filename: [bcp.fmt]myFormatFile.fmt
The default name for the format file is bcp.fmt, but you can specify a different file name if you choose.
For a data file that uses a single data format for its file-storage type, such as character or native format, you can quickly create a format file without exporting or importing data by using the format option. This approach has the advantages of being easy and of allowing you to create either an XML format file or a non-XML format file. For more information, see Creating a Format File.
In This Section
This section contains the following topics.
Contains information about specifying the file storage type in a bcp command.
Contains information about specifying the prefix length in a bcp command.
Contains information about specifying the field length in a bcp command.
Contains information about specifying field and row terminators in a bcp command.
Contains information about how character-formatted data is stored in an exported data file.