LOAD, UNLOAD, and dbload

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LOAD, UNLOAD, and dbload

The LOAD statement is moderately fast and easy to use, but it can only accept specified data formats. You usually use LOAD with data that is prepared with an UNLOAD statement.

You can use the UNLOAD statement in DB–Access to unload selected rows from a table into a text file.

To load tables, use LOAD or dbload. To manipulate a data file that you are loading or to access a database while it is loading, use the dbload utility. The cost of the flexibility is the time you spend creating the dbload command file and slower execution. When possible, use the LOAD statement, which is faster than dbload.

Figure 2 summarizes questions to help you choose among these methods.

Figure 2. Choosing Among dbimport, dbload, and LOAD

begin figure description - To move an entire database, use dbimport. If you need to commit inserts during the load or skip some rows before starting to load, use dbload. Otherwise, use LOAD if the data format is acceptable to LOAD. - end figure description

The dbload utility gives you a great deal of flexibility, but it is not as fast as the other methods, and you must prepare a command file to control the input. You can use dbload with data in a variety of formats.

The dbload utility offers the following advantages over the LOAD statement:

You can use dbload to load data from input files that were created with a variety of format arrangements. The dbload command file can accommodate data from entirely different database management systems.
You can specify a starting point in the load by directing dbload to read but ignore x number of rows.
You can specify a batch size so that after every x number of rows are inserted, the insert is committed.
You can limit the number of bad rows read, beyond which dbload ends.

The cost of dbload flexibility is the time and effort spent creating the dbload command file, which is required for dbload operation. The input files are not specified as part of the dbload command line, and neither are the tables into which the data is inserted. This information is contained in the command file.