A single script often requires two schemas, one each for the source and target. It is also possible to use multiple schemas for the source data if all rows are UNION-compatible. Two schemas are UNION-compatible if their corresponding columns have exactly the same data type attributes (type, length, precision and scale); that is, other than their column names, the schemas are identical. If the schemas are UNION-compatible Teradata PT combines data from the sources, each being extracted by a different producer operator using a different schema, into a single output data stream using its UNION ALL feature. For information, see UNION ALL: Combining Data from Multiple Sources.