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CREATE TAG

CREATE TAG creates a tag with the given name in a graph space.

OpenCypher compatibility

Tags in nGQL are similar to labels in openCypher. But they are also quite different. For example, the ways to create them are different.

  • In openCypher, labels are created together with vertices in CREATE statements.
  • In nGQL, tags are created separately using CREATE TAG statements. Tags in nGQL are more like tables in MySQL.

Prerequisites

Running the CREATE TAG statement requires some privileges for the graph space. Otherwise, Nebula Graph throws an error.

Syntax

To create a tag in a specific graph space, you must specify the current working space with the USE statement.

CREATE TAG [IF NOT EXISTS] <tag_name>
    (
      <prop_name> <data_type> [NULL | NOT NULL] [DEFAULT <default_value>] [COMMENT '<comment>']
      [{, <prop_name> <data_type> [NULL | NOT NULL] [DEFAULT <default_value>] [COMMENT '<comment>']} ...] 
    )
    [TTL_DURATION = <ttl_duration>]
    [TTL_COL = <prop_name>]
    [COMMENT = '<comment>'];
Parameter Description
IF NOT EXISTS Detects if the tag that you want to create exists. If it does not exist, a new one will be created. The tag existence detection here only compares the tag names (excluding properties).
<tag_name> The tag name must be unique in a graph space. Once the tag name is set, it can not be altered. The rules for permitted tag names are the same as those for graph space names. For prohibited names, see Keywords and reserved words.
<prop_name> The name of the property. It must be unique for each tag. The rules for permitted property names are the same as those for tag names.
<data_type> Shows the data type of each property. For a full description of the property data types, see Data types and Boolean.
NULL \| NOT NULL Specifies if the property supports NULL | NOT NULL. The default value is NULL.
DEFAULT Specifies a default value for a property. The default value can be a literal value or an expression supported by Nebula Graph. If no value is specified, the default value is used when inserting a new vertex.
COMMENT The remarks of a certain property or the tag itself. The maximum length is 256 bytes. By default, there will be no comments on a tag.
TTL_DURATION Specifies the life cycle for the property. The property that exceeds the specified TTL expires. The expiration threshold is the TTL_COL value plus the TTL_DURATION. The default value of TTL_DURATION is 0. It means the data never expires.
TTL_COL Specifies the property to set a timeout on. The data type of the property must be int or timestamp. A tag can only specify one field as TTL_COL. For more information on TTL, see TTL options.

Examples

nebula> CREATE TAG IF NOT EXISTS player(name string, age int);

# The following example creates a tag with no properties.
nebula> CREATE TAG IF NOT EXISTS no_property(); 

# The following example creates a tag with a default value.
nebula> CREATE TAG IF NOT EXISTS player_with_default(name string, age int DEFAULT 20);

# In the following example, the TTL of the create_time field is set to be 100 seconds.
nebula> CREATE TAG IF NOT EXISTS woman(name string, age int, \
        married bool, salary double, create_time timestamp) \
        TTL_DURATION = 100, TTL_COL = "create_time";

Implementation of the operation

Trying to use a newly created tag may fail because the creation of the tag is implemented asynchronously.

Nebula Graph implements the creation of the tag in the next heartbeat cycle. To make sure the creation is successful, take one of the following approaches:

  • Find the new tag in the result of SHOW TAGS. If you cannot, wait a few seconds and try again.
  • Wait for two heartbeat cycles, i.e., 20 seconds.

To change the heartbeat interval, modify the heartbeat_interval_secs parameter in the configuration files for all services.


Last update: November 10, 2021
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