情況

搜尋第一個評估為 true 的條件並返回其關聯值。如果沒有條件符合，則返回 null。

from employees
derive distance = case [
  city == "Calgary" => 0,
  city == "Edmonton" => 300,
]

SELECT
  *,
  CASE
    WHEN city = 'Calgary' THEN 0
    WHEN city = 'Edmonton' THEN 300
    ELSE NULL
  END AS distance
FROM
  employees

要設定預設值，可以使用 true 條件：

from employees
derive distance = case [
  city == "Calgary" => 0,
  city == "Edmonton" => 300,
  true => "Unknown",
]

SELECT
  *,
  CASE
    WHEN city = 'Calgary' THEN 0
    WHEN city = 'Edmonton' THEN 300
    ELSE 'Unknown'
  END AS distance
FROM
  employees