Using the Oracle Bulk Loader -2

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Overview

To use the Oracle bulk loader, you need a control file, which specifies how data should be loaded into the database; and a data file, which specifies what data should be loaded. You will learn how to create these files in turn.

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Creating the Control File

A simple control file has the following form:

LOAD DATA
INFILE <datafile>
APPEND INTO TABLE <tablename>
FIELDS TERMINATED BY '<separator>'
(<list load="" to="" names="" attribute="" all="" of="">)</list></separator></tablename></datafile>

• <datafile></datafile> is the name of the data file. If you did not give a file name extension for <datafile></datafile>, Oracle will assume the default extension ".dat". Therefore, it is a good idea to name every data file with an extension, and specify the complete file name with the extension.
• <tablename> </tablename> is the name of the table to which data will be loaded. Of course, it should have been created already before the bulk load operation.
• The optional keyword APPEND says that data will be appended to <tablename> </tablename> . If APPEND is omitted, the table must be empty before the bulk load operation or else an error will occur.
• <separator></separator> specifies the field separator for your data file. This can be any string. It is a good idea to use a string that you know will never appear in the data, so the separator will not be confused with data fields.
• Finally, list the names of attributes of <tablename> </tablename> that are set by your data file, separated by commas and enclosed in parentheses. This list need not be the complete list of attributes in the actual schema of the table, nor must it be arranged in the same order as the attributes when the table was created -- sqlldr will match attributes to by their names in the table schema. Any attributes unspecified in the list of attributes will be set to NULL.

As a concrete example, here are the contents of a control file test.ctl:

LOAD DATA
INFILE test.dat
INTO TABLE test
FIELDS TERMINATED BY '|'
(i, s)

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Creating the Data File

Each line in the data file specifies one tuple to be loaded into <tablename> </tablename> . It lists, in order, values for the attributes in the list specified in the control file, separated by <separator></separator>. As a concrete example, test.dat might look like:

1|foo
2|bar
3| baz

Recall that the attribute list of test specified in test.ctl is (i, s), where i has the type int, and s has the type char(10). As the result of loading test.dat, the following tuples are inserted into test:

(1, 'foo')
(2, 'bar')
(3, ' baz')

Some Notes of Warning

• Note that the third line of test.dat has a blank after "|". This blank is not ignored by the loader. The value to be loaded for attribute s is ' baz', a four-character string with a leading blank. It is a common mistake to assume that 'baz', a three-character string with no leading blank, will be loaded instead. This can lead to some very frustrating problems that you will not notice until you try to query your loaded data, because ' baz' and 'baz' are different strings.

• Oracle literally considers every single line to be one tuple, even an empty line! When it tries to load data from an empty line, however, an error would occur and the tuple will be rejected. Some text editors love to add multiple newlines to the end of a file; if you see any strange errors in your .log file about tuples with all NULL columns, this may be the cause. It shouldn't affect other tuples loaded.

• If you are using a Microsoft text editor, such as MSWord, you will find that Bill Gates believes in ending lines with the sequence <cr> (carriage return) <lf> (line feed). The UNIX world uses only <lf>, so each <cr> becomes ^M, the last character of strings in your load file. That makes it impossible for you ever to match a stored string in an SQL query. Here's how you remove ^M symbols from your file. Let's say the file with ^M symbols is bad_myRel.dat. Then the following command will create myRel.dat without ^M symbols: </cr></lf></lf></cr>

               cat bad_myRel.dat | tr -d '\015' > myRel.dat
  

  If you're an emacs fan, type in the following sequence to modify your current buffer:

                  ESC-x replace-string CTRL-q CTRL-m ENTER ENTER
  

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  Loading Your Data

  The Oracle bulk loader is called sqlldr. It is a UNIX-level command, i.e., it should be issued directly from your UNIX shell, rather than within sqlplus. A bulk load command has the following form:

  sqlldr <yourname> control=<ctlfile> log=<logfile> bad=<badfile></badfile></logfile></ctlfile></yourname>

  Everything but sqlldr is optional -- you will be prompted for your username, password, and control file. <ctlfile></ctlfile> is the name of the control file. If no file name extension is provided, sqlldr will assume the default extension ".ctl". The name of the data file is not needed on the command line because it is specified within the control file. You may designate <logfile></logfile> as the log file. If no file name extension is provided, ".log" will be assumed. sqlldr will fill the log file with relevant information about the bulk load operation, such as the number of tuples loaded, and a description of errors that may have occurred. Finally, you may designate <badfile></badfile> as the file where bad tuples (any tuples for which an error occurs on an attempt to load them) are recorded (if they occur). Again, if no file extension is specified, Oracle uses ".bad". If no log file or bad file are specified, sqlldr will use the name of the control file with the .log and .bad extensions, respectively.

  As a concrete example, if sally wishes to run the control file test.ctl and have the log output stored in test.log, then she should type

  sqlldr sally control=test.ctl log=test.log

  Reminder: Before you run any Oracle commands such as sqlldr and sqlplus, make sure you have already set up the correct environment by sourcing /afs/ir/class/cs145/all.env (see Getting Started With Oracle).

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  Loading Without a Separate Data File

  It is possible to use just the control file to load data, instead of using a separate data file. Here is an example:

  LOAD DATA
  INFILE *
  INTO TABLE test
  FIELDS TERMINATED BY '|'
  (i, s)
  BEGINDATA
  1|foo
  2|bar
  3| baz

  The trick is to specify "*" as the name of the data file, and use BEGINDATA to start the data section in the control file.

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  Loading DATE Data

  The DATE datatype can have its data loaded in a format you specify with considerable flexibility. First, suppose that you have created a relation with an attribute of type DATE:

  CREATE TABLE foo (
      i int,
      d date
  );

  In the control file, when you describe the attributes of foo being loaded, you follow the attribute d by its type DATE and a date mask. A date mask specifies the format your date data will use. It is a quoted string with the following conventions:
  • Sequences of d, m, or y, denote fields in your data that will be interpreted as days, months, years, respectively. As with almost all of SQL, capitals are equally acceptable, e.g., MM is a month field.
  • The lengths of these fields specify the maximum lengths for the corresponding values in your data. However, the data can be shorter.
  • Other characters, such as dash, are treated literally, and must appear in your data if you put them in the mask.
  Here is an example control file:

  LOAD DATA
  INFILE *
  INTO TABLE foo
  FIELDS TERMINATED BY '|'
  (i, d DATE 'dd-mm-yyyy')
  BEGINDATA
  1|01-01-1990
  2|4-1-1998

  Notice that, as illustrated by the second tuple above, a field can be shorter than the corresponding field in the date mask. The punctuation "-" tells the loader that the day and month fields of the second tuple terminate early.

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  Loading Long Strings

  String fields that may be longer than 255 characters, such as for data types CHAR(2000) or VARCHAR(4000), require a special CHAR(n) declaration in the control file. For example, if table foo was created as

  CREATE TABLE foo (x VARCHAR(4000));

  Then a sample control file should look like:

  LOAD DATA
  INFILE <datafile>
  INTO TABLE foo
  FIELDS TERMINATED BY '|'
  (x CHAR(4000))</datafile>

  Note that the declaration takes the form CHAR(n) regardless of whether the field type was declared as CHAR or VARCHAR.

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  Entering NULL Values

  You may specify NULL values simply by entering fields in your data file without content. For example, if we were entering integer values into a table with schema (a, b, c) specified in the .ctl file, the following lines in the data file:

  3||5
  |2|4
  1||6
  ||7

  would result in inserting the following tuples in the relation:

  (3, NULL, 5)
  (NULL, 2, 4)
  (1, NULL, 6)
  (NULL, NULL, 7)

  Keep in mind that any primary keys or other constraints requiring that values be non-NULL will reject tuples for which those attributes are unspecified.

  Note:If the final field in a given row of your data file will be unspecified (NULL), you have to include the line TRAILING NULLCOLS after the FIELDS TERMINATED BY line in your control file, otherwise sqlldr will reject that tuple. sqlldr will also reject a tuple whose columns are all set to NULL in the data file.

  If you do not wish to enter values for any row of a given column, you can, as mentioned above, leave that column out of the attribute list altogether.