Updated on 2024-07-19 GMT+08:00

Constraints and Limitations

The restrictions on using DSC to migrate data from TD are as follows:

  • DSC is used only for syntax migration and not for data migration.
  • If the SELECT clause of a subquery contains an aggregate function when the IN or NOT IN operator is converted to EXISTS or NOT EXISTS, the migration may fail.

Teradata

  • If a case statement containing FORMAT is not enclosed in parentheses, this statement will not be processed.
    Examples are as follows:
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    case when column1='0' then column1='value' end (FORMAT 'YYYYMMDD')as alias1
    

    In this example, case when column1='0' then column1='value' end is not enclosed in parentheses and it will not be processed.

  • If SELECT * and QUALIFY clauses are both used in an input query, the migrated query returns an additional column for the QUALIFY clause.

    An example is as follows:

    Teradata query

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    SELECT * FROM dwQErrDtl_mc.C03_CORP_TIME_DPSIT_ACCT
    WHERE 1 = 1
    AND Data_Dt = CAST( '20150801' AS DATE FORMAT 'YYYYMMDD' )
    QUALIFY ROW_NUMBER( ) OVER( PARTITION BY Agt_Num, Agt_Modif_Num ORDER BY NULL ) = 1;
    

    Query after migration

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    SELECT * FROM (
    SELECT *, ROW_NUMBER( ) OVER( PARTITION BY Agt_Num, Agt_Modif_Num ORDER BY NULL ) AS ROW_NUM1
    FROM dwQErrDtl_mc.C03_CORP_TIME_DPSIT_ACCT
    WHERE 1 = 1
    AND Data_Dt = CAST( '20150801' AS DATE )
    ) Q1
    WHERE Q1.ROW_NUM1 = 1;
    

    In the migrated query, the ROW_NUMBER( ) OVER( PARTITION BY Agt_Num ,Agt_Modif_Num ORDER BY NULL ) AS ROW_NUM1 column is returned additionally.

  • Named references to a table in a query cannot be migrated from subqueries or functions.
    For example, if the input query contains a table named foo, DSC will not migrate any named references to the table from a subquery (foo.fooid) or when called from a function (getfoo(foo.fooid)).
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    SELECT * FROM foo
     WHERE foosubid IN (
                         SELECT foosubid
                           FROM getfoo(foo.fooid) z
                          WHERE z.fooid = foo.fooid
                          );
    
  • The database with the schema name should be changed to SET SESSION CURRENT_SCHEMA.

    TD Syntax

    Syntax After Migration

    DATABASE SCHTERA 
    SET SESSION CURRENT_SCHEMA TO SCHTERA
  • The table-specific keyword MULTISET VOLATILE is provided in the input file, but the keyword is not supported by GaussDB(DWS). Therefore, the tool replaces it with the LOCAL TEMPORARY/UNLOGGED keyword during the migration process. Use the session_mode configuration parameter to set the default table type (SET/MULTISET) for CREATE TABLE.