将现有的mysql列更改为JSON数据类型

Question

我试图将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

它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 != ''

新的request_json列已更新.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 JSON数据类型

...

• 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)