DBC.COLUMNS¶
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.
Note
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.
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).
Note
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.
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
;