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SELECT

Define output fields by completely replacing the current field set.

Syntax​

SELECT assignmentClause [, assignmentClause]* [,]?

Parameters​

  • assignmentClause - Either a simple expression or an assignment (identifier = expression)

Description​

The SELECT command completely redefines the field structure of the dataset, replacing all existing fields with only those you explicitly specify. Unlike SET, which adds or modifies fields while preserving others, SELECT gives you complete control over the output schema.

Each assignmentClause can be either a simple expression (which preserves the original field name when referencing a field) or an assignment that creates a new field with a specified name. When you use assignment syntax, the identifier becomes the field name and the expression provides the value. When you don't use assignment syntax, Hamelin automatically generates field names based on the expression (see Automatic Field Names for details).

The SELECT command evaluates expressions against the current row context. You can reference any fields available at that point in the pipeline, including original dataset fields, fields created by previous SET commands, and fields from joined datasets.

  • SET - Add or modify fields while preserving others