Constraints and Limitations

Updated on 2025-01-09 GMT+08:00

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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:

       
          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

     
        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

     
        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)).

      
         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.