Question

我正在尝试将MySQL列从varchar（9000）NULL更改为MySQL 5.7中的新JSON数据类型。该列包含有效的JSON字符串，但某些值为null。当我尝试以下内容时：

alter table log modify request json

失败并出现以下错误：

Invalid JSON text: "The document is empty." at position 0 in value for column '#sql-2f36_168a6.request'

但是，当我创建一个新列时：

alter table log add request_json json

然后插入相同的数据：

update log set request_json=json where request != ''

更新新的request_json列。如何将现有列修改为JSON数据类型并保留JSON数据而不创建新列？

Answer 1

12.6 The JSON Data Type

...


自动验证存储在JSON列中的JSON文档。无效的文档会产生错误。


...

mysql> SHOW CREATE TABLE `log`\G
*************************** 1. row ***************************
       Table: log
Create Table: CREATE TABLE `log` (
  `request` json DEFAULT NULL
) ENGINE=InnoDB
1 row in set (0,00 sec)

mysql> SELECT `request`, JSON_VALID(`request`)
    -> FROM `log`;
+-----------------+-----------------------+
| request         | JSON_VALID(`request`) |
+-----------------+-----------------------+
| {"type": "bug"} |                     1 |
| NULL            |                  NULL |
| NULL            |                  NULL |
+-----------------+-----------------------+
3 rows in set (0,00 sec)

mysql> UPDATE `log`
    -> SET `request` = ''
    -> WHERE `request` IS NULL;
ERROR 3140 (22032): Invalid JSON text: "The document is empty." at position 0 in value for column 'log.request'.

尝试：

mysql> DROP TABLE IF EXISTS `log`;
Query OK, 0 rows affected (0,00 sec)

mysql> CREATE TABLE IF NOT EXISTS `log` (
    ->   `request` VARCHAR(9000) NULL
    -> );
Query OK, 0 rows affected (0,01 sec)

mysql> INSERT INTO `log`
    ->   (`request`)
    -> VALUES
    ->   ('{"type": "bug"}'),
    ->   (NULL),
    ->   ('');
Query OK, 3 rows affected (0,00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT `request`, JSON_VALID(`request`)
    -> FROM `log`;
+-----------------+-----------------------+
| request         | JSON_VALID(`request`) |
+-----------------+-----------------------+
| {"type": "bug"} |                     1 |
| NULL            |                  NULL |
|                 |                     0 |
+-----------------+-----------------------+
3 rows in set (0,00 sec)

mysql> ALTER TABLE `log` MODIFY `request` JSON;
ERROR 3140 (22032): Invalid JSON text: "The document is empty." at position 0 in value for column '#sql-1bab_4.request'.

mysql> UPDATE `log`
    -> SET `request` = NULL
    -> WHERE `request` = '';
Query OK, 1 row affected (0,00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> ALTER TABLE `log` MODIFY `request` JSON;
Query OK, 3 rows affected (0,00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT `request`, JSON_VALID(`request`)
    -> FROM `log`;
+-----------------+-----------------------+
| request         | JSON_VALID(`request`) |
+-----------------+-----------------------+
| {"type": "bug"} |                     1 |
| NULL            |                  NULL |
| NULL            |                  NULL |
+-----------------+-----------------------+
3 rows in set (0,00 sec)

mysql> SHOW CREATE TABLE `log`\G
*************************** 1. row ***************************
       Table: log
Create Table: CREATE TABLE `log` (
  `request` json DEFAULT NULL
) ENGINE=InnoDB
1 row in set (0,00 sec)

将现有的mysql列更改为JSON数据类型

1 个答案: