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Lambda Expressions

Applies to: ✅ Data 360 SQL ✅ Tableau Hyper API

Lambda expressions are anonymous functions you pass as arguments to higher-order functions such as ARRAY_TRANSFORM and ARRAY_FILTER. They enable element-wise operations on arrays without writing separate function definitions.

Syntax

lambda <param1>[, <param2>, ...]: <expression>

Arguments

  • <param1>, <param2>, ...: One or more parameter names that represent the elements from the input arrays. The number of parameters must match the number of array arguments passed to the function.
  • <expression>: Any valid SQL expression that uses the parameters. The expression is evaluated once for each element (or tuple of elements) in the input arrays.

Considerations

  • Lambda expressions can only be used as arguments to functions that accept them, such as ARRAY_TRANSFORM and ARRAY_FILTER.
  • The parameter names are local to the lambda and don't conflict with column names in the outer query.
  • Lambda expressions can't reference columns or variables from the outer query scope.
  • The return type of the lambda expression is inferred from the expression. If the expression returns only NULL, you must cast it to a specific type.
  • Data 360 uses the Python / DuckDB-style lambda syntax (lambda x: expr), not the Spark / Snowflake-style arrow syntax (x -> expr).

Examples

Single Parameter Lambda

Use a single parameter when operating on one array.

SELECT array_transform(ARRAY[1, 2, 3], lambda x: x * 2) AS doubled;

Returns [2, 4, 6].

Multiple Parameter Lambda

Use multiple parameters when operating on multiple arrays in parallel.

SELECT array_transform(ARRAY[1, 2, 3], ARRAY[10, 20, 30], lambda x, y: x + y) AS sums;

Returns [11, 22, 33].

Lambda with Conditional Logic

Use CASE expressions within lambdas for conditional transformations.

SELECT array_transform(ARRAY[1, 5, 3], ARRAY[4, 2, 6], lambda x, y:
  CASE WHEN x > y THEN x ELSE y END
) AS maximums;

Returns [4, 5, 6].

Lambda for Filtering

Return a boolean expression to filter array elements.

SELECT array_filter(ARRAY[1, 2, 3, 4, 5, 6], lambda x: x % 2 = 0) AS evens;

Returns [2, 4, 6].

Lambda with String Operations

Lambdas work with any data type.

SELECT array_transform(
  ARRAY['hello', 'world'],
  ARRAY['!', '?'],
  lambda x, y: upper(x) || y
) AS result;

Returns ["HELLO!", "WORLD?"].

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