ydb/yql/essentials/docs/en/_includes/cast_examples.md

SELECT
    CAST("12345" AS Double),                -- 12345.0
    CAST(1.2345 AS Uint8),                  -- 1
    CAST(12345 AS String),                  -- "12345"
    CAST("1.2345" AS Decimal(5, 2)),        -- 1.23
    CAST("xyz" AS Uint64) IS NULL,          -- true, because it failed
    CAST(-1 AS Uint16) IS NULL, -- true, a negative integer cast to an unsigned integer
    CAST([-1, 0, 1] AS List<Uint8?>),             -- [null, 0, 1]
        --The item type is optional: the failed item is cast to null.
    CAST(["3.14", "bad", "42"] AS List<Float>),   -- [3.14, 42]
        --The item type is not optional: the failed item has been deleted.
    CAST(255 AS Uint8),                     -- 255
    CAST(256 AS Uint8) IS NULL -- true, out of range