DBC.COLUMNS view is a table containing information about table and view columns, stored procedures, or macro parameters. The view includes the following column names: DatabaseName, TableName, ColumnName, ColumnFormat, ColumnTitle, ColumnType, and DefaultValue. In GaussDB(DWS), this table is equivalent to the information_schema.columns table.

This feature requires one time execution of the custom script file DSC/scripts/teradata/db_scripts/mig_fn_get_datatype_short_name.sql.

For more information about the steps to execute the file, refer to Operating Environment and Prerequisites respectively.

The DSC migrates the following dbc.columns to their corresponding information_schema columns.

**Table 1** Migration of dbc.columns to information_schema columns
dbc.columns	information_schema.columns
ColumnName	Column_Name
ColumnType	mig_fn_get_datatype_short_name (data_Type)
ColumnLength	character_maximum_length
DecimalTotalDigits	numeric_precision
DecimalFractionalDigits	numeric_scale
databasename	table_schema
tablename	table_name
ColumnId	ordinal_position

The following assumptions are made when migrating dbc.columns:

The FROM clause will contain only the dbc.columns TABLE NAME
COLUMN NAME can be in the form of column_name or schema_name.table_name.column_name.

Migration of dbc.columns is not supported for the following cases:

If the FROM clause has an ALIAS for dbc.columns table name (dbc.columns alias).
If dbc.columns is combined with other tables (FROM dbc.columns alias1, table1 alias2 OR dbc.columns alias1 join table1 alias2).

If the input SELECT statement includes dbc.column COLUMN NAMES directly, then the tool will migrate the input column names as an ALIAS. For example, the input column name DecimalFractionalDigits is migrated to numeric_scale with an ALIAS DecimalFractionalDigits.

Example:

Input:

SEL
       columnid
       ,DecimalFractionalDigits
     FROM
       dbc.columns
;

Output:

SELECT
       ordinal_position columnid
       ,numeric_scale DecimalFractionalDigits
     FROM
       information_schema.columns
;

For table names and schema names, the DSC will convert all string values to lowercase. To maintain case-sensitivity, the table/schema names should be within double quotes. In the following input example, "Test" will not be converted to lower case.
1 2 3 4 5 6
SELECT TableName FROM dbc . columns WHERE dbc.columns.databasename = '"Test"';

Input: dbc.columns table with all supported columns

SELECT
'$AUTO_DB_IP'
,objectdatabasename
,objecttablename
,'$TX_DATE_10'
,''
,'0' 
,FirstStepTime
,FirstRespTime
,RowCount
,cast(RowCount*sum(case when T2.ColumnType ='CV' then T2.ColumnLength/3 else  T2.ColumnLength end) as decimal(38,0))
,'3' 
,''
,'BAK_CLR_DATA'
,'2'
,''
FROM TMP_clr_information T1
inner join dbc.columns T2
on T1.objectdatabasename =T2.DatabaseName
and T1.objecttablename =T2.TableName
where  T2.DatabaseName not in (
sel child from dbc.children 
where parent='$FCRM_DB'
)
group by 1,2,3,4,5,6,7,8,9,11,12,13,14,15;

Output

SELECT
          '$AUTO_DB_IP'
          ,objectdatabasename
          ,objecttablename
          ,'$TX_DATE_10'
          ,''
          ,'0'                                
          ,FirstStepTime
          ,FirstRespTime
          ,RowCount
          ,CAST( RowCount * SUM ( CASE WHEN mig_fn_get_datatype_short_name ( T2.data_Type ) = 'CV' THEN T2.character_maximum_length / 3 ELSE T2.character_maximum_length END ) AS DECIMAL( 38 ,0 ) )                        
          ,'3'                                
          ,''
          ,'BAK_CLR_DATA'
          ,'2'
          ,''
     FROM
          TMP_clr_information T1 INNER JOIN information_schema.columns T2
               ON T1.objectdatabasename = T2.table_schema
          AND T1.objecttablename = T2.table_name
     WHERE
          NOT EXISTS (
               SELECT
                         child
                    FROM
                         dbc.children
                    WHERE
                         child = T2.table_schema
                         AND( parent = '$FCRM_DB' )
          )
     GROUP BY
          1 ,2 ,3 ,4 ,5 ,6 ,7 ,8 ,9 ,11 ,12 ,13 ,14 ,15
;

Input: dbc.columns table with TABLE NAME

SELECT
          TRIM( ColumnName )
          ,UPPER( dbc.columns.ColumnType )
     FROM
          dbc . columns
     WHERE
          dbc.columns.databasename = '"Test"'
     ORDER BY
          dbc.columns.ColumnId
;

Output

SELECT
          TRIM( Column_Name )
          ,UPPER( mig_fn_get_datatype_short_name ( information_schema.columns.data_Type ) )
     FROM
          information_schema.columns
     WHERE
          information_schema.columns.table_schema = CASE
               WHEN TRIM( '"Test"' ) LIKE '"%'
               THEN REPLACE( SUBSTR( '"Test"' ,2 ,LENGTH( '"Test"' ) - 2 ) ,'""' ,'"' )
               ELSE LOWER( '"Test"' )
          END
     ORDER BY
          information_schema.columns.ordinal_position
;