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 an external table in a database.

An external table is a key feature in a database management system. Generally, a table in a database stores data in the storage space of the database, while an external table stores data in an external storage service.

When you create an external table, you must 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. An external table is read-only. You can use it in a query statement, but you cannot perform DML operations on it. You cannot define constraints or create indexes on an external table.

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 mapped to the definition columns of the external table in order.
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 this parameter.
AS	Manually specifies column mappings. 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 specify manual column mappings, automatic mappings become invalid, and you must define mappings for all columns manually.
LOCATION	The path where the external table files are stored. Generally, external table data files are stored in a single directory, which can contain subdirectories. When you create an external table, the table automatically collects all files in the directory. The local `LOCATION` parameter 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. `secure_file_priv` specifies the file path that OBServer nodes have the permission to access. `local_file_path` must be a subpath of `secure_file_priv`. The remote `LOCATION` parameter 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 object storage paths, separate the parameters in the object storage path with `&`. Make sure that the characters in the parameter value you entered are uppercase or lowercase letters, digits, and characters from the `/-_$+=` set or the wildcard character. If you enter characters other than the aforesaid ones, the setting may fail.
FORMAT	The format of external files. `TYPE`: the type of external files. Currently, only CSV files are supported. `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 MySQL mode, see Character sets. If this parameter is not specified, the default value is UTF8MB4, which is supported in MySQL mode. `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 specifies 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 in the file. The default value is `FALSE`, which specifies not to remove leading and trailing spaces from fields in the file. `EMPTY_FIELD_AS_NULL`: specifies whether to treat an empty string as `NULL`. The default value is `FALSE`, which specifies not to treat an empty string as `NULL`.
PATTERN	A regular expression pattern that is used to filter files in the directory specified by the `LOCATION` parameter. For each file in the directory specified by the `LOCATION` parameter, if the file path matches the pattern, the external table accesses the file. Otherwise, the external table skips the file. If this parameter is not specified, the external table, by default, accesses all files in the directory specified by the `LOCATION` parameter. The external table stores the list of files that match the `PATTERN` in the system tables of the database. When the external table is scanned, the list is used to access external files.

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 missing 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 conflicts with a query on the external table, the result of the query may be unexpected. Therefore, avoid modifying the external file while it is being queried.
If a new file is added to an external directory, the external table does not access the new file. If you want 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 to be imported, in the /home/admin/test directory on the local OBServer node that is connected.

The following example shows how to set 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