这将做您想要的。它将第四个字段读入局部变量，然后如果该局部变量最终包含空字符串，则将实际字段值设置为NULL：
LOAD DATA INFILE '/tmp/testdata.txt'
INTO TABLE moo
FIELDS TERMINATED BY ","
LINES TERMINATED BY "\n"
(one, two, three, @vfour, five)
SET four = NULLIF(@vfour,'')
;
如果它们都可能为空，则将它们全部读入变量并具有多个SET语句，如下所示：
LOAD DATA INFILE '/tmp/testdata.txt'
INTO TABLE moo
FIELDS TERMINATED BY ","
LINES TERMINATED BY "\n"
(@vone, @vtwo, @vthree, @vfour, @vfive)
SET
one = NULLIF(@vone,''),
two = NULLIF(@vtwo,''),
three = NULLIF(@vthree,''),
four = NULLIF(@vfour,'')
;
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