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FROM

Access rows from datasets.

Syntax​

FROM fromClause [, fromClause]* [,]?

Parameters​

  • fromClause - Either a dataset identifier or an alias assignment (alias = dataset)

Description​

The FROM command pulls rows from datasets. When you specify multiple datasets, Hamelin combines all rows from all datasets.

Multiple datasets use automatic type expansion. Fields with identical names are aligned, while unique fields appear with NULL values for rows from datasets that don't contain them.

When you use aliases with the assignment syntax (alias = dataset), the alias becomes a struct containing all fields from that dataset. This lets you organize field access and track data lineage.