CREATE EXTERNAL TABLE|V4.2.0| docs|Distributed Database

CREATE EXTERNAL TABLE

Last Updated：2025-12-03 10:23:56 Updated

Description

This statement is used to create a new external table in the database.

External tables are a key feature in database management systems. Typically, tables in a database store data in the database's storage space, while external tables store data in external storage services.

When you create an external table, you need to specify the file path and file format of the data. After that, you can use the external table to read data from the external storage service. External tables are read-only. You can use them in query statements, but you cannot perform DML operations on them. You cannot define constraints or create indexes on external tables.

Syntax

CREATE EXTERNAL TABLE <table_name>
    ( [ <column_name> <column_type> [AS <expr>] ]
      [ , <column_name> <column_type> [AS <expr>] ]
      [ , ... ] )
    LOCATION = '<string>'
    FORMAT = (
      TYPE = 'CSV'
      LINE_DELIMITER = '<string>' | <expr>
      FIELD_DELIMITER = '<string>' | <expr>
      ESCAPE = '<character>' | <expr>
      FIELD_OPTIONALLY_ENCLOSED_BY = '<character>' | <expr>
      ENCODING = 'charset'
      NULL_IF = ('<string>' | <expr>, '<string>' | <expr> ...)
      SKIP_HEADER = <int>
      SKIP_BLANK_LINES = { TRUE | FALSE }
      TRIM_SPACE = { TRUE | FALSE }
      EMPTY_FIELD_AS_NULL = { TRUE | FALSE }
    )
    [ PATTERN = '<regex_pattern>' ]

Parameter description

Parameter	Description
table_name	The name of the external table to be created.
column_name	The name of a column in the external table. By default, the data columns in the file are automatically matched with the definition columns of the external table in sequence.
column_type	The type of a column in the external table. You cannot define constraints such as `DEFAULT`, `NOT NULL`, `UNIQUE`, `CHECK`, `PRIMARY KEY`, or `FOREIGN KEY` in the column type.
AS	Manually specifies the mappings between columns. When the order of columns in a file is different from that in the external table, you can specify the correspondence between a column in the external table and the Nth column in the file by using the pseudo-column `metadata$filecol{N}`. For example, `c2 INT AS (metadata$filecol4)` indicates that the `c2` column in the external table corresponds to the fourth column in the file. Note that if you manually specify the column mappings, the automatic mappings become invalid, and you must manually specify mappings for all columns.
LOCATION	The path where the external table is stored. Generally, the data file of an external table is stored in a separate directory, which can contain subdirectories. When you create an external table, the system automatically collects all files in the specified directory. The local `LOCATION` is specified in the `LOCATION = '[file://] local_file_path'` format, where `local_file_path` can be a relative path or an absolute path. If an absolute path is used, the current directory must be the installation directory of OceanBase Database. The `secure_file_priv` variable specifies the file path that the OBServer node has the permission to access. `local_file_path` can only be a subpath of `secure_file_priv`. The remote `LOCATION` is specified in the `LOCATION = '{oss\\|cos}://$ACCESS_ID:$ACCESS_KEY@$HOST/remote_file_path'` format, where `$ACCESS_ID`, `$ACCESS_KEY`, and `$HOST` are the access information required when you access OSS/COS. These sensitive access information are stored in encrypted form in the system tables of the database. Notice When you use an object storage path, separate the parameters in the object storage path with `&`. Make sure that the characters in the parameter values you entered are uppercase or lowercase letters, digits, or `/-_$+=`. If you enter characters other than the aforesaid ones, the setting may fail.
FORMAT	The format of the external file. `TYPE`: the type of the external file. Only the CSV format is supported at present. `LINE_DELIMITER`: the line delimiter for CSV files. The default value is `LINE_DELIMITER='\n'`. `FIELD_DELIMITER`: the field delimiter for CSV files. The default value is `FIELD_DELIMITER='\t'`. `ESCAPE`: the escape character for CSV files. It can be only 1 byte in length. The default value is `ESCAPE ='\'`. `FIELD_OPTIONALLY_ENCLOSED_BY`: the characters that enclose field values in CSV files. The default value is an empty string. `ENCODING`: the character set encoding format of the file. For the character sets supported in Oracle mode, see Character set. If you do not specify the encoding, UTF8MB4 is used by default. `NULL_IF`: the string that is treated as `NULL`. The default value is an empty string. `SKIP_HEADER`: specifies to skip the file header and indicates the number of lines to skip. `SKIP_BLANK_LINES`: specifies whether to skip blank lines. The default value is `FALSE`, which specifies not to skip blank lines. `TRIM_SPACE`: specifies whether to remove leading and trailing spaces from fields. The default value is `FALSE`, which specifies not to remove leading and trailing spaces from fields. `EMPTY_FIELD_AS_NULL`: specifies whether to treat empty strings as `NULL`. The default value is `FALSE`, which specifies not to treat empty strings as `NULL`.
PATTERN	A regular pattern string that is used to filter files in the `LOCATION` directory. For each file in the directory specified by `LOCATION`, if the file path matches the pattern string, the external table accesses the file. Otherwise, the external table skips the file. If you do not specify this parameter, the external table, by default, accesses all files in the directory specified by `LOCATION`. The external table stores the list of files that match the `LOCATION`-specified path and the `PATTERN`-specified pattern in the system tables of the database. When the external table scans files, it accesses external files based on this list. The file list can be automatically updated or manually updated.

Considerations

If an external file is deleted, the file no longer exists in the file list when you access the file list. In this case, the external table ignores the non-existent file.
If an external file is modified, the external table accesses the latest data of the external file. If the modification of the external file is concurrent with a query on the external table, the result of the query may be unexpected. Therefore, avoid modifying external files while they are being queried.
If a new file is added to an external directory, the external table accesses only the files in the file list. To add the new file to the file list of the external table, you must update the file list of the external table.

Examples

Set the secure_file_priv path to /home/admin/ and place the CSV file extdata.csv, which contains the data to be imported, in the /home/admin/test directory on the local OBServer node that is connected.

Here is an example of setting the global secure path.
```
obclient> SET GLOBAL secure_file_priv = ""
Query OK, 0 rows affected 
obclinet> \q
Bye
```
Note

After you set the secure_file_priv variable to a global variable, you must execute the \q statement to make the setting take effect.

The CSV file contains the following data:
```
1,'Dave','Smith','d******h@outlook.com','friend',32 
2,'Xena','Johnson','x******n@outlook.com','contact',45
3,'Fred','Jackon','f******n@outlook.com','co-worker',19
4,'Alma','Tyler','a******r@outlook.com','friend',53
```

obclient> CREATE EXTERNAL TABLE contacts ( 
    id    INT, 
    firstname  VARCHAR(100), 
    lastname   VARCHAR(100), 
    email      VARCHAR(255), 
    category   CHAR(30), 
    age        NUMBER )
   LOCATION = '/home/admin/test/'
   FORMAT = (
     TYPE = 'CSV'
     FIELD_DELIMITER = ','
     FIELD_OPTIONALLY_ENCLOSED_BY =''''
    )PATTERN ='extdata.csv';

Query data from the contacts table.

obclient> SELECT * FROM contacts;
+------+-----------+----------+----------------------+--------------------------------+------+
| ID   | FIRSTNAME | LASTNAME | EMAIL                | CATEGORY                       | AGE  |
+------+-----------+----------+----------------------+--------------------------------+------+
|    1 | Dave      | Smith    | d******h@outlook.com | friend                         |   32 |
|    2 | Xena      | Johnson  | x******n@outlook.com | contact                        |   45 |
|    3 | Fred      | Jackon   | f******n@outlook.com | co-worker                      |   19 |
|    4 | Alma      | Tyler    | a******r@outlook.com | friend                         |   53 |
+------+-----------+----------+----------------------+--------------------------------+------+
4 rows in set

References

Create an external table

Manage external files

Update the file list of an external table