SQL:如何获取一列句子行中所有字符串的总和

SELECT SUM(LENGTH(word)) AS total_length
FROM (
  SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(sentence, ' ', n), ' ', -1) AS word
  FROM sentences
  CROSS JOIN (
    SELECT 1 + units.i + tens.i * 10 AS n
    FROM (
      SELECT 0 AS i UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL
      SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
    ) units
    CROSS JOIN (
      SELECT 0 AS i UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL
      SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
    ) tens
  ) numbers
  WHERE word <> ''
) words;