eldenmoon commented on code in PR #3339:
URL: https://github.com/apache/doris-website/pull/3339#discussion_r2780394886
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i18n/zh-CN/docusaurus-plugin-content-docs/version-4.x/sql-manual/basic-element/sql-data-types/semi-structured/VARIANT.md:
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@@ -388,9 +464,71 @@ SELECT * FROM tbl WHERE v['str'] MATCH 'Doris';
| `VARCHAR` | ✔ | ✔ |
| `JSON` | ✔ | ✔ |
+### 基于 Schema Template 自动 CAST
+
+当 VARIANT 列定义了 schema template 时，且 `enable_variant_schema_auto_cast` 设为 true
时，语义分析阶段会为命中 schema template 的子列自动插入对应类型的 CAST，无需自行手写。
+
+- 覆盖 SELECT、WHERE、ORDER BY、GROUP BY、HAVING、JOIN KEY 或聚合参数等场景。
+- 若需关闭此行为，将 `enable_variant_schema_auto_cast` 设为 false。
+
+示例：
+```sql
+CREATE TABLE t (
+ id BIGINT,
+ data VARIANT<'num_*': BIGINT, 'str_*': STRING>
+);
+
+-- 1) 过滤 + 排序
+SELECT id
+FROM t
+WHERE data['num_a'] > 10
+ORDER BY data['num_a'];
+
+-- 2) 分组 + 聚合 + Alias
+SELECT data['str_name'] AS username, SUM(data['num_a']) AS total
+FROM t
+GROUP BY username
+HAVING data['num_a'] > 100;
+
+-- 3) JOIN ON
+SELECT *
+FROM t1 JOIN t2
+ON t1.data['num_id'] = t2.data['num_id'];
+```
+
+**注意**：自动 CAST 功能无法感知给定的 Path 是否为叶子，它只是对所有符合 schema template 规则的 Path 都加对应的
CAST。
+
+因此，对于下述这种情况需要额外注意，为保证结果正确，请设置 `enable_variant_schema_auto_cast` 设为 false，并手动添加
CAST。
+
+```sql
+-- Schema Template：所有 int_* 视为 INT
+CREATE TABLE t (
+ id INT,
+ data VARIANT<'int_*': INT>
+);
+
+INSERT INTO t VALUES
+(1, '{"int_1": 1, "int_nested": {"level1_num_1": 1011111, "level1_num_2":
102}}');
+
+-- 自动 CAST 开启
+SET enable_variant_schema_auto_cast = true;
+
+-- int_nested 匹配 int_*，错误自动 CAST 为 INT，查询结果返回 NULL
+SELECT
+ data['int_nested']
+FROM t;
+
+-- 自动 CAST 关闭
+SET enable_variant_schema_auto_cast = false;
Review Comment:
这个加上回归测试
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