Updating mysql tables from external file
If a conversion error occurs, then the datafile may not contain all the rows that were processed up to that point and the datafile will not be readable.
To avoid problems with conversion errors causing the operation to fail, the datatype of the column in the external table should match the datatype of the column in the database.
You are not given direct access to those files outside of the Oracle database unless you have the appropriate operating system privileges.
Similarly, the Oracle database requires permission from the operating system to read and write files in the directories.
An unload operation also creates a metadata stream that describes the contents of the data stream.
The information in the metadata stream is required for loading the data stream.
In the context of external tables, loading data refers to the act of reading data from an external table and loading it into a table in the database.
Unloading data refers to the act of reading data from a table in the database and inserting it into an external table.
The following file, record, and data characteristics make it impossible for a file to be processed in parallel: clause should specify as many files as there are degrees of parallelism.
statement generates a flow of data from the external data source to the Oracle SQL engine, where data is processed.
As data from the external source is parsed by the access driver and provided to the external table interface, it is converted from its external representation to its Oracle internal datatype. The data stream that is unloaded is in a proprietary format and contains all the column data for every row being unloaded.
You must also know enough about SQL to be able to create an external table and perform queries against it.
This chapter discusses the following topics: CREATE TABLE emp_load 2 (employee_number CHAR(5), 3 employee_dob CHAR(20), 4 employee_last_name CHAR(20), 5 employee_first_name CHAR(15), 6 employee_middle_name CHAR(15), 7 employee_hire_date DATE) 8 ORGANIZATION EXTERNAL 9 (TYPE ORACLE_LOADER 10 DEFAULT DIRECTORY def_dir1 11 ACCESS PARAMETERS 12 (RECORDS DELIMITED BY NEWLINE 13 FIELDS (employee_number CHAR(2), 14 employee_dob CHAR(20), 15 employee_last_name CHAR(18), 16 employee_first_name CHAR(11), 17 employee_middle_name CHAR(11), 18 employee_hire_date CHAR(10) date_format DATE mask "mm/dd/yyyy" 19 ) 20 ) 21 LOCATION ('info.dat') 22 ); Table created.
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A directory object maps a name to a directory name on the file system.