MySQL从CSV数据加载NULL值

Question

我有一个文件,可以包含3到4列数字,用逗号分隔.当空字段位于行的末尾时,将定义空字段:

1,2,3,4,5
1,2,3,,5
1,2,3

下表是在MySQL中创建的:

+-------+--------+------+-----+---------+-------+
| Field | Type   | Null | Key | Default | Extra |
+-------+--------+------+-----+---------+-------+
| one   | int(1) | YES  |     | NULL    |       | 
| two   | int(1) | YES  |     | NULL    |       | 
| three | int(1) | YES  |     | NULL    |       | 
| four  | int(1) | YES  |     | NULL    |       | 
| five  | int(1) | YES  |     | NULL    |       | 
+-------+--------+------+-----+---------+-------+

我正在尝试使用MySQL LOAD命令加载数据:

LOAD DATA INFILE '/tmp/testdata.txt' INTO TABLE moo FIELDS 
TERMINATED BY "," LINES TERMINATED BY "\n";

结果表:

+------+------+-------+------+------+
| one  | two  | three | four | five |
+------+------+-------+------+------+
|    1 |    2 |     3 |    4 |    5 | 
|    1 |    2 |     3 |    0 |    5 | 
|    1 |    2 |     3 | NULL | NULL | 
+------+------+-------+------+------+

问题在于,当原始数据中的字段为空且未定义时,MySQL由于某种原因不使用列默认值(即NULL)并使用零.当字段完全丢失时,正确使用NULL.

不幸的是,我必须能够在这个阶段区分NULL和0,所以任何帮助都将受到赞赏.

谢谢S.

编辑

SHOW WARNINGS的输出:

+---------+------+--------------------------------------------------------+
| Level   | Code | Message                                                |
+---------+------+--------------------------------------------------------+
| Warning | 1366 | Incorrect integer value: '' for column 'four' at row 2 | 
| Warning | 1261 | Row 3 doesn't contain data for all columns             | 
| Warning | 1261 | Row 3 doesn't contain data for all columns             | 
+---------+------+--------------------------------------------------------+

Answer 1

这将做你想要的.它将第四个字段读入局部变量,然后将实际字段值设置为NULL,如果局部变量最终包含空字符串:

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,'')
;

如果它们都可能是空的,那么你将它们全部读入变量并有多个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,'')
;

Answer 2

MySQL手册说:

使用LOAD DATA INFILE读取数据时,使用''更新空列或缺少列.如果要在列中使用NULL值,则应在数据文件中使用\ N. 在某些情况下也可以使用文字"NULL".

所以你需要用\ N替换空白像这样:

1,2,3,4,5
1,2,3,\N,5
1,2,3

Answer 3

根据数据库配置,行为会有所不同.在严格模式下,这会抛出错误,否则会发出警告.以下查询可用于标识数据库配置.

mysql> show variables like 'sql_mode';

Answer 4

预处理您的输入 CSV 以用 \N 替换空白条目。

尝试使用正则表达式：s/,,/,\n,/g 和 s/,$/,\N/g

祝你好运。