演示示例。

必须导入的源 CSV 内容：

review_id,user,text
123,John,This is
multiline 1, which
contains a comma.
456,Jim,This is
miltiline 2, which contains
commas, 'quote' chars and "double quote" chars.

此数据必须导入到的表：

CREATE TABLE test (review_id INT, user VARCHAR(255), review_text TEXT);

将数据加载到表中的查询：

LOAD DATA INFILE 'C:/ProgramData/MySQL/MySQL Server 8.0/Uploads/test.csv'
INTO TABLE test
FIELDS TERMINATED BY '\0' ENCLOSED BY '' ESCAPED BY ''
LINES TERMINATED BY '\r\n'
IGNORE 1 LINES
(@line)
SET review_id = (@review_id := CASE WHEN @line REGEXP '^\\d'
                                    THEN SUBSTRING_INDEX(@line, ',', 1)
                                    ELSE @review_id
                                    END
                                    ),
    user =  (@user := CASE WHEN @line REGEXP '^\\d'
                           THEN SUBSTRING_INDEX(SUBSTRING_INDEX(@line, ',', 2), ',', -1)
                           ELSE @user
                           END
                           ),
    review_text = (@review_text := CASE WHEN @line REGEXP '^\\d'
                                        THEN SUBSTRING(@line FROM 2 + LENGTH(SUBSTRING_INDEX(@line, ',', 2)))
                                        ELSE CONCAT_WS(' ', @review_text, @line)
                                        END
                                        );

加载后表格数据状态：

DELETE t1
FROM test t1
JOIN test t2 USING (user)
WHERE t1.review_text < t2.review_text;