COMMENT (Comment-Retrieving Form) - Teradata Database

SQL Data Manipulation Language

Product
Teradata Database
Release Number
15.10
Language
English (United States)
Last Update
2018-10-06
dita:id
B035-1146
lifecycle
previous
Product Category
Teradata® Database

Retrieves a previously placed comment on a database object or definition.

where:

 

Syntax Element …

Specifies …

object_kind_1

a mandatory database object kind specification.

The valid specifications for object_kind_1 are not all database objects. Triggers and views, for example, are definitions of actions or conceptual groups rather than database objects.

You must specify the following database object kinds to retrieve a comment for the kind of object they represent.

  • COLUMN
  • FUNCTION
  • GLOP SET
  • GROUP
  • MACRO
  • METHOD
  • PROCEDURE
  • PROFILE
  • ROLE
  • TRIGGER
  • TYPE
  • VIEW
  • object_kind_2

    an optional database object kind specification.

    You can specify the following database object kinds to retrieve a comment for the kind of object they represent, but they are optional.

  • DATABASE
  • TABLE
  • USER
  • FILE
  • The semantics of the COMMENT statement require that if you specify an object kind, you must specify the keyword TABLE for any hash or join index whose comment you want to retrieve; however, because TABLE is not a mandatory object kind specification, you are not required to specify it.

    If you omit the object_kind when you retrieve a comment for a file, the object_name must contain the whole path to the file, for example, dbname.uifname.

    database_name | user_name

    the containing database or user for object_name if it is not contained by the current database or user.

    You cannot specify a database name or user name if object_kind is GROUP.

    For the rules to use in naming database objects, see SQL Fundamentals.

    object_name

    the name of the object for which a comment is to be retrieved, including:

  • Parameter in a macro, stored procedure, or user­‑defined function.
  • Column in a user base table, error table, hash index, join index, or view.
  • Specific function, macro, profile, role, stored procedure, base table, error table, hash index, join index, trigger, or view name contained by a database or user.
  • Database or user.
  • UDT. You can retrieve a comment on a particular attribute of a structured UDT by specifying database_name.udt_name.attribute_name.
  • A method. You must use the specific method name.
  • A GLOP set.
  • If you do not precede the object name with an object kind keyword, the system attempts to deduce the object from the level of qualification in the name. Use the fully‑qualified name to avoid ambiguity.

    Let x.y.z indicate the qualification hierarchy, with x being the highest, or coarsest grained, level and z the lowest, or most finely grained.

    object_name

    (continued)

    If you specify a hierarchy level of x, the specified object is implied to be one of the following:

  • Database
  • User
  • If you specify a hierarchy level of x.y, the specified object is implied to be one of the following:

  • Base table
  • Error table
  • GLOP set
  • Hash index
  • Join index
  • Macro
  • Profile
  • Role
  • Stored procedure
  • Trigger
  • User‑defined function
  • View within database or user x.
  • If you specify a hierarchy level of x.y.z, the specified object is implied to be one of the following:

  • Macro parameter
  • Stored procedure parameter
  • Structured UDT attribute
  • Table column
  • UDF parameter
  • View column within GLOP set, UDF, UDT, macro, stored procedure, profile, role, base table, trigger, or view y contained in database or user x.
  • COMMENT is a Teradata extension to the ANSI SQL:2011 standard.

    None.

    None.

    These rules apply to using the comment‑retrieving form of the COMMENT statement:

  • COMMENT (Comment‑Retrieving Form) is treated as a DML statement for transaction processing, so it can be used in 2PC session mode. For a brief description of the two‑phase commit protocol, see Introduction to Teradata.
  • You can specify a COMMENT (Comment‑Retrieving Form) request at any point within the boundaries of an explicit transaction in Teradata session mode.

  • To retrieve a comment, do not specify a comment string following the specification of the object name.
  •  

    IF you …

    THEN the system …

    specify a comment string

    does one of the following things:

  • If the specified object has no existing comment, then Teradata Database places the specified comment string for the object in the data dictionary.
  • If the specified object has an existing comment, then Teradata Database replaces the existing comment in the data dictionary with the newly specified string.
  • do not specify a comment string

    does one of the following things:

  • If the specified object has no existing comment, then Teradata Database returns a null.
  • If the specified object has an existing comment, then Teradata Database returns the text of that comment as it is stored in the data dictionary.
  • You cannot specify a containing database or user name if the object kind you specify is GROUP.