Levenshtein在T-SQL中的距离

WITH LevenshteinCTE (s1, s2, s1len, s2len, distance) AS (
    SELECT s1, s2, LEN(s1) AS s1len, LEN(s2) AS s2len, 0 AS distance
    FROM (SELECT @s1 AS s1, @s2 AS s2) AS Source
    WHERE LEN(@s1) = 0 OR LEN(@s2) = 0

    UNION ALL

    SELECT s1, s2, s1len, s2len,
        CASE
            WHEN SUBSTRING(s1, s1len, 1) = SUBSTRING(s2, s2len, 1) THEN distance
            ELSE distance + 1
        END
    FROM LevenshteinCTE
    WHERE s1len > 0 AND s2len > 0
        AND SUBSTRING(s1, s1len, 1) <> SUBSTRING(s2, s2len, 1)
        AND s1len > LEN(s1) - s2len
)
SELECT distance AS LevenshteinDistance
FROM LevenshteinCTE
WHERE s1len = 0 OR s2len = 0