BULK INSERT Imports a data file into a database table or view in a user-specified format.
BULK INSERT
[ database_name . [ schema_name ] . | schema_name . ] [ table_name | view_name ]
FROM ‘data_file‘
[ WITH
(
[ [ , ] BATCHSIZE = batch_size ]
[ [ , ] CHECK_CONSTRAINTS ]
[ [ , ] CODEPAGE = { ‘ACP‘ | ‘OEM‘ | ‘RAW‘ | ‘code_page‘ } ]
[ [ , ] DATAFILETYPE =
{ ‘char‘ | ‘native‘| ‘widechar‘ | ‘widenative‘ } ]
[ [ , ] FIELDTERMINATOR = ‘field_terminator‘ ]
[ [ , ] FIRSTROW = first_row ]
[ [ , ] FIRE_TRIGGERS ]
[ [ , ] FORMATFILE = ‘format_file_path‘ ]
[ [ , ] KEEPIDENTITY ]
[ [ , ] KEEPNULLS ]
[ [ , ] KILOBYTES_PER_BATCH = kilobytes_per_batch ]
[ [ , ] LASTROW = last_row ]
[ [ , ] MAXERRORS = max_errors ]
[ [ , ] ORDER ( { column [ ASC | DESC ] } [ ,...n ] ) ]
[ [ , ] ROWS_PER_BATCH = rows_per_batch ]
[ [ , ] ROWTERMINATOR = ‘row_terminator‘ ]
[ [ , ] TABLOCK ]
[ [ , ] ERRORFILE = ‘file_name‘ ]
)]
Critical Arguments
‘data_file ‘
Is the full path of the data file that contains data to import into the specified table or view. BULK INSERT can import data from a disk (including network, floppy disk, hard disk, and so on).
data_file must specify a valid path from the server on which SQL Server is running. If data_file is a remote file, specify the Universal Naming Convention (UNC) name. A UNC name has the form \\Systemname\ShareName\Path\FileName.
For example, \\SystemX\DiskZ\Sales\update.txt.
BATCHSIZE =batch_size
Specifies the number of rows in a batch. Each batch is copied to the server as one transaction. If this fails, SQL Server commits or rolls back the transaction for every batch. By default, all data in the specified data file is one batch. For information about performance considerations, see "Remarks," later in this topic.
CHECK_CONSTRAINTS
Specifies that all constraints on the target table or view must be checked during the bulk-import operation. Without the CHECK_CONSTRAINTS option, any CHECK and FOREIGN KEY constraints are ignored, and after the operation, the constraint on the table is marked as not-trusted.
UNIQUE and PRIMARY KEY constraints are always enforced. When importing into a character column that is defined with a NOT NULL constraint, BULK INSERT inserts a blank string when there is no value in the text file.
At some point, you must examine the constraints on the whole table. If the table was non-empty before the bulk-import operation, the cost of revalidating the constraint may exceed the cost of applying CHECK constraints to the incremental data.
A situation in which you might want constraints disabled (the default behavior) is if the input data contains rows that violate constraints. With CHECK constraints disabled, you can import the data and then use Transact-SQL statements to remove the invalid data.
KEEPIDENTITY
Specifies that identity value or values in the imported data file are to be used for the identity column. If KEEPIDENTITY is not specified, the identity values for this column are verified but not imported and SQL Server automatically assigns unique values based on the seed and increment values specified during table creation. If the data file does not contain values for the identity column in the table or view, use a format file to specify that the identity column in the table or view is to be skipped when importing data; SQL Server automatically assigns unique values for the column. For more information, see DBCC CHECKIDENT (Transact-SQL).
For more information, see about keeping identify values see Keep Identity Values When Bulk Importing Data (SQL Server).
KEEPNULLS
Specifies that empty columns should retain a null value during the bulk-import operation, instead of having any default values for the columns inserted. For more information, see Keep Nulls or Use Default Values During Bulk Import (SQL Server).
Performance Considerations
If the number of pages to be flushed in a single batch exceeds an internal threshold, a full scan of the buffer pool might occur to identify which pages to flush when the batch commits. This full scan can hurt bulk-import performance. A likely case of exceeding the internal threshold occurs when a large buffer pool is combined with a slow I/O subsystem. To avoid buffer overflows on large machines, either do not use the TABLOCK hint (which will remove the bulk optimizations) or use a smaller batch size (which preserves the bulk optimizations).
Because computers vary, we recommend that you test various batch sizes with your data load to find out what works best for you.
参考文档：
MSDN BULK INSERT (Transact-SQL)