CopyStageTransformer

Overview

Transforms DataStage COPY stages to SQL SELECT statements. Handles both dataset inputs (mapped to Snowflake tables) and stage inputs (CTE references).

Stage Type: COPY Output: SQL SELECT with column filtering and renaming

Capabilities

• Maps DataStage datasets to Snowflake tables
• Reads from upstream stages via schema_registry
• Applies keep clause column filtering
• Handles column type definitions from modify section
• Deduplicates columns for stages with multiple outputs

DataStage Stage Example

Input (.dsx format)

#### STAGE: CopyDimension
## Operator
copy
## General options
[ident('CopyDimension')]
## Inputs
0< [ds] '[&"$PathDataSetWarehouse"]/DimLookup.ds'
## Outputs
0> [-pp; modify (
  SOURCE_KEY:nullable decimal[38,10]=SOURCE_KEY;
  DIMENSION_KEY:nullable decimal[15,0]=DIMENSION_KEY;
keep
  SOURCE_KEY,DIMENSION_KEY;
)] 'CopyDimension:Out_Process.v'

Dataset Mapping Configuration

dataset_table_mapping = {
    'DimLookup.ds': 'PUBLIC.DIM_LOOKUP_TABLE'
}

Generated SQL Output

SELECT
    SOURCE_KEY,
    DIMENSION_KEY
FROM PUBLIC.DIM_LOOKUP_TABLE

Output Schema

[
  {
    "name": "SOURCE_KEY",
    "type": "number"
  },
  {
    "name": "DIMENSION_KEY",
    "type": "number"
  }
]

How It Works

1. Reads dataset path from inputs: [ds] '[&"$PathDataSetWarehouse"]/DimLookup.ds'
2. Maps dataset to Snowflake table using dataset_table_mapping
3. Extracts column types from modify section:
   • decimal[38,10] → number
   • decimal[15,0] → number
   • string[max=N] → string
4. Applies keep filter to select only specified columns: SOURCE_KEY, DIMENSION_KEY
5. Generates SELECT with filtered column list from mapped table

Type Mapping

DataStage types are converted to Snowflake types:

Column Filtering

The transformer supports three filtering modes:

1. Keep clause - Only specified columns are selected

   keep
     SOURCE_KEY,DIMENSION_KEY;

2. Drop clause - All columns except specified ones

   drop
     TEMP_COLUMN;

3. No filter - All columns from source

Reading from Stages vs Datasets

Dataset Input

## Inputs
0< [ds] '[&"$PathDataSetDwfatos"]/MyDataset.ds'

Requires mapping in dataset_table_mapping.

Stage Input

## Inputs
0< [] 'PreviousStage:output.v'

Reads schema from schema_registry and references upstream CTE.

Limitations

• Requires dataset_table_mapping for dataset inputs (no automatic table discovery)
• Column type inference depends on modify section or schema_registry being populated
• Multiple output links result in deduplicated column list
• View mappings not supported (column renames in COPY should use downstream MODIFY stage)

Related Transformers

• ModifyStageTransformer - For column renames and filters without reading datasets
• ImportStageTransformer - For file inputs (CSV, sequential files)
• InputStageTransformer - For Oracle table/SQL inputs