Lambda functions

Limits

• Subqueries are not supported, such as x->2+(SELECT3).

• Aggregations are not supported, such as x -> max(y).

Syntax

The syntax is: parameter list -> expression or code block

• Parameter list: The parameters that the lambda function accepts. The list can be empty or contain one or more parameters.

• ->: Separates the parameter list from the expression or code block.

Examples

• Example 1: Calculate the square of values in an array column

  SELECT numbers,transform(numbers, n -> n * n) as squared_numbers
  FROM (
      VALUES (ARRAY(1, 2)),(ARRAY(3, 4)),(ARRAY(5, 6, 7))
  ) AS t(numbers);

  The following result is returned:

  +------------+-----------------+
  | numbers    | squared_numbers |
  +------------+-----------------+
  | [5,6,7]    | [25,36,49]      |
  | [3,4]      | [9,16]          |
  | [1,2]      | [1,4]           |
  +------------+-----------------+

• Example 2: Convert an array to a string

  SELECT transform(prices, n -> CAST(n AS STRING ) || '$') as price_tags
  FROM (
      VALUES
          (ARRAY(100, 200)),(ARRAY(30, 4))
  ) AS t(prices);

  The following result is returned:

  +------------+
  | price_tags |
  +------------+
  | ["30$","4$"] |
  | ["100$","200$"] |
  +------------+

• Example 3: Calculate the value of a linear function

  SELECT xvalues, a, b,
         transform(xvalues, x -> a * x + b) as linear_function_values
  FROM (
      VALUES (ARRAY(1, 2), 10, 5),(ARRAY(3, 4), 4, 2)
  ) AS t(xvalues, a, b);

  The following result is returned:

  +------------+------------+------------+------------------------+
  | xvalues    | a          | b          | linear_function_values |
  +------------+------------+------------+------------------------+
  | [3,4]      | 4          | 2          | [14,18]                |
  | [1,2]      | 10         | 5          | [15,25]                |
  +------------+------------+------------+------------------------+