CREATE TAG Syntax¶
CREATE TAG [IF NOT EXISTS] <tag_name> ([<create_definition>, ...]) [tag_options] <create_definition> ::= <prop_name> <data_type> <tag_options> ::= <option> [, <option> ...] <option> ::= TTL_DURATION [=] <ttl_duration> | TTL_COL [=] <prop_name> | DEFAULT <default_value>
Nebula Graph's schema is composed of tags and edges, either of which may have properties.
CREATE TAG statement defines a tag with the given name.
The features of this syntax are described in the following sections:
IF NOT EXISTS¶
You can use the
If NOT EXISTS keywords when creating tags. This keyword automatically detects if the corresponding tag exists. If it does not exist, a new one is created. Otherwise, no tag is created.
NOTE: The tag existence detection here only compares the tag name (excluding properties).
The name of tags must be unique within the space. Once the name is defined, it can not be altered. The rules of tag names are the same as those for names of spaces. See Schema Object Name for detail.
Property Name and Data Type¶
prop_name indicates the name of properties. It must be unique for each tag.
data_type represents the data type of each property. For more information about data types that Nebula Graph supports, see data-type section.
NULL and NOT NULL constrain are not supported yet when creating tags (comparing with relational databases).
- Default Constraint
You can set the default value of a property when creating a tag with the
DEFAULTconstraint. The default value will be added to all new vertices if no other value is specified. The default value can be any of the data type supported by Nebula Graph or expressions. Also you can write a user-specified value if you don't want to use the default one.
Alterto change the default value is not supported.
Time-to-Live (TTL) Syntax¶
ttl_duration specifies the life cycle of vertices (or edges). Data that exceeds the specified TTL will expire. The expiration threshold is the specified TTL_COL value plus the TTL_DURATION.
If the value for ttl_duration is zero, the vertices or edges will not expire.
The data type of prop_name must be either int64 or timestamp.
- single TTL definition
Only a single TTL_COL field can be specified.
Details about TTL refer to the TTL Doc.
nebula> CREATE TAG course(name string, credits int); nebula> CREATE TAG notag(); -- empty properties nebula> CREATE TAG player_with_default(name string, age int DEFAULT 20); -- age is set to 20 by default
nebula> CREATE TAG woman(name string, age int, married bool, salary double, create_time timestamp) TTL_DURATION = 100, TTL_COL = "create_time"; -- time interval is 100s, starting from the create_time filed nebula> CREATE TAG icecream(made timestamp, temperature int) TTL_DURATION = 100, TTL_COL = "made", -- Data expires after TTL_DURATION