MySQL Server 支持無模式的數(shù)據(jù)存儲(chǔ)菲茬，功能特性如下：

1. JSON 數(shù)據(jù)類型娱俺。JSON 值在新增 / 更新時(shí)會(huì)被分析、驗(yàn)證刷晋，然后儲(chǔ)存為優(yōu)化了的二進(jìn)制格式盖高。在讀取時(shí)不需任何分析或驗(yàn)證。
2. JSON 函數(shù)眼虱。有 20 多個(gè) SQL 函數(shù)用于搜索喻奥、操作、創(chuàng)建 JSON 值捏悬。
3. 生成列撞蚕。其工作方式很像函數(shù)索引，并能夠?qū)?JSON 的一部分進(jìn)行提取或索引过牙。

優(yōu)化器在查詢 JSON 數(shù)據(jù)時(shí)甥厦，會(huì)自動(dòng)通過生成列尋找匹配的索引。
在例子35中寇钉，“用戶設(shè)置” 被儲(chǔ)存在了JSON列中刀疙，查詢 “更新時(shí)通知我” 的用戶，會(huì)使用全表掃描扫倡。通過增加一個(gè)虛擬生成列谦秧，EXPLAIN 展示出能使用到索引了：

例子35：“用戶設(shè)置” 的無模式表示法

CREATE TABLE users (
  id INT NOT NULL auto_increment,
  username VARCHAR(32) NOT NULL,
  preferences JSON NOT NULL,      -- “用戶設(shè)置” 使用了 JSON 類型
  PRIMARY KEY (id),
  UNIQUE (username)
);

INSERT INTO users
 (id,username,preferences)
VALUES
 (NULL, 'morgan', '{"layout": "horizontal", "warn_before_delete": false, "notify_on_updates": true}'),
 (NULL, 'wes', '{"layout": "horizontal", "warn_before_delete": false, "notify_on_updates": false}'),
 (NULL, 'jasper', '{"layout": "horizontal", "warn_before_delete": false, "notify_on_updates": false}'),
 (NULL, 'gus', '{"layout": "horizontal", "warn_before_delete": false, "notify_on_updates": false}'),
 (NULL, 'olive', '{"layout": "horizontal", "warn_before_delete": false, "notify_on_updates": false}');

EXPLAIN FORMAT=JSON 
SELECT * FROM users WHERE preferences->"$.notify_on_updates" = true;

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.00"
    },
    "table": {
      "table_name": "users",          
      "access_type": "ALL",         # 查詢 “用戶設(shè)置” 時(shí)，使用了全表掃描
      "rows_examined_per_scan": 5,
      "rows_produced_per_join": 5,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "1.00",
        "eval_cost": "1.00",
        "prefix_cost": "2.00",
        "data_read_per_join": "280"
      },
      "used_columns": [
        "id",
        "username",
        "preferences"
      ],
      "attached_condition": "(json_extract(`test`.`users`.`preferences`,'$.notify_on_updates') = TRUE)"
    }
  }
}

例子36：添加虛擬生成列

-- 添加虛擬列。注意 JSON類型 訪問和修改的語法疚鲤。
ALTER TABLE users 
  ADD notify_on_updates TINYINT AS (preferences->"$.notify_on_updates"),
  ADD INDEX(notify_on_updates);

EXPLAIN FORMAT=JSON 
SELECT * FROM users WHERE preferences->"$.notify_on_updates" = true;

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.20"
    },
    "table": {
      "table_name": "users",    
      "access_type": "ref",         # 使用到了索引
      "possible_keys": [
        "notify_on_updates"
      ],
      "key": "notify_on_updates",
      "used_key_parts": [
        "notify_on_updates"
      ],
      "key_length": "2",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "1.00",
        "eval_cost": "0.20",
        "prefix_cost": "1.20",
        "data_read_per_join": "56"
      },
      "used_columns": [
        "id",
        "username",
        "preferences",
        "notify_on_updates"
      ]
    }
  }
}

譯自：
JSON and Generated Columns - The Unofficial MySQL 8.0 Optimizer Guide