Question

创建示例数据库和表以供使用。

create database `test`;
use `test`;
create table `test` (`value` float(10,2) null);
insert into test (value) values (null);
select value  from test;
+-------+
| value |
+-------+
|  NULL |
+-------+
1 row in set (0.00 sec)

现在我想创建一个txt文件，当您加载它时，可以将空数据加载到测试表中。

delete from test;

这是我的名为test.txt的数据文件，显示在vim（：set list）中。

将文件加载到表中。

LOAD DATA LOCAL INFILE  "test.txt"
INTO TABLE test
FIELDS TERMINATED BY '\t'
LINES TERMINATED BY '\n' \w;
select value from test;
+-------+
| value |
+-------+
|  0.00 |
|  0.00 |
|  0.00 |
|  0.00 |
|  0.00 |
+-------+

在我的情况下，如何使用文件加载null字段的value数据？
如何创建这种数据文件，加载后其值字段为null？

运行时环境：win10 + mysql-5.7。

select version();
+-----------+
| version() |
+-----------+
| 5.7.22    |
+-----------+
1 row in set (0.03 sec)

使用set list在vim中显示test.txt文件。

\N$
\N^I$

case：未设置

不使用(value) SET value = (CASE WHEN @value IS NULL THEN NULL ELSE @value END)加载它。

LOAD DATA LOCAL INFILE  "f:/test.txt"
INTO TABLE test
FIELDS TERMINATED BY '\t'
LINES TERMINATED BY '\n' \W;

输出：

Warning (Code 1265): Data truncated for column 'value' at row 1
Warning (Code 1262): Row 2 was truncated; it contained more data than there were input columns

select * from  test;
+-------+
| value |
+-------+
|  0.00 |
|  NULL |
+-------+

case：with set
用(value) SET value = (CASE WHEN @value IS NULL THEN NULL ELSE @value END)加载它。

delete from test;
LOAD DATA LOCAL INFILE  "f:/test.txt"
INTO TABLE test
FIELDS TERMINATED BY '\t'
LINES TERMINATED BY '\n' 
(value)SET value = (CASE WHEN @value IS NULL THEN NULL ELSE @value END) \W;

输出：

Warning (Code 1265): Data truncated for column 'value' at row 1
Warning (Code 1262): Row 2 was truncated; it contained more data than there were input columns

 select * from test;
+-------+
| value |
+-------+
|  NULL |
|  NULL |
+-------+

谢谢@Schwern。

LOAD DATA LOCAL INFILE  "f:/test.txt"
INTO TABLE test
FIELDS TERMINATED BY '\t'
LINES TERMINATED BY '\r\n'  \W;

在没有警告的情况下，任何一种都可以正常工作。

Answer 1

您可以使用\N。

问题是您所有的输入行都有一个额外的空白字段。 Tab终止该字段，就像逗号一样。您已使用它，就像将其括在引号中一样。例如，您的第一行^Inull^I是三个字段。第一个是空的。第二个包含null。第三个是空的。

MySQL应该说过类似的话

Query OK, 5 rows affected, 8 warnings (0.01 sec)
Records: 5  Deleted: 0  Skipped: 0  Warnings: 8

您可以使用show warnings阅读这些警告。

+---------+------+---------------------------------------------------------------------------+
| Level   | Code | Message                                                                   |
+---------+------+---------------------------------------------------------------------------+
| Warning | 1265 | Data truncated for column 'value' at row 1                                |
| Warning | 1262 | Row 1 was truncated; it contained more data than there were input columns |
| Warning | 1265 | Data truncated for column 'value' at row 2                                |
| Warning | 1262 | Row 2 was truncated; it contained more data than there were input columns |
| Warning | 1265 | Data truncated for column 'value' at row 3                                |
| Warning | 1265 | Data truncated for column 'value' at row 4                                |
| Warning | 1262 | Row 4 was truncated; it contained more data than there were input columns |
| Warning | 1265 | Data truncated for column 'value' at row 5                                |
+---------+------+---------------------------------------------------------------------------+

您需要的是这个

\N$

请注意，lines terminated by对Unix和Windows换行符敏感。从文档中...

如果在Windows系统上生成了文本文件，则可能必须使用LINES TERMINATED BY '\r\n'来正确读取该文件，因为Windows程序通常使用两个字符作为行终止符。

这说明了您收到的警告。

如何用文件加载空数据？

1 个答案: