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From traflm <...@git.apache.org>
Subject [GitHub] incubator-trafodion pull request #895: [TRAFODION-2412]update sql reference ...
Date Mon, 26 Dec 2016 16:02:39 GMT
Github user traflm commented on a diff in the pull request:

    https://github.com/apache/incubator-trafodion/pull/895#discussion_r93874161
  
    --- Diff: docs/sql_reference/src/asciidoc/_chapters/sql_language_elements.adoc ---
    @@ -137,6 +137,74 @@ You can define specific default settings for columns when the table
is created.
     default settings for columns within tables. The default setting for a column is the value
inserted in a row when an INSERT
     statement omits a value for a particular column.
     
    +<<<
    +[[identity_columns]]
    +== Identity Columns
    +
    +Trafodion introduces the ability defining an identity clause against a table column defined
using a numeric type. The syntax is shown below.
    +
    +```
    +GENERATED
    +[ALWAYS | BY DEFAULT]
    +AS IDENTITY [(identity_options)]
    +```
    +
    +Ignoring the identity_options, which match those of the <<create_sequence_statement,CREATE_SEQUENCE_Statement>>,
this syntax allows us to use three variations on the identity functionality.
    +
    +[[syntax_description_of_identity_columns]]
    +=== Syntax Description of Identity Columns
    +* `ALWAYS`
    ++
    +Using ALWAYS forces the use of the identity. If an insert statement references the identity
column, even to specify a NULL value, an error is produced.
    +
    +* `BY DEFAULT`
    ++
    +Using BY DEFAULT allows you to use the identity if the column isn't referenced in the
insert statement, but if the column is referenced, the specified value will be used in place
of the identity. Attempting to specify the value NULL in this case results in an error, since
identity columns are always NOT NULL.
    --- End diff --
    
    line is too long, need to limit each line's length, to generate a better HTML displaying.

    This is a general comment, please consider to change all 'long lines' below into fixed
width line.


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