docs: improve data management (#2146)

Signed-off-by: Dennis Zhuang <[email protected]>

Author: killme2008

docs/reference/sql/create.md

@@ -261,7 +261,7 @@ create table if not exists metrics(
 with('merge_mode'='last_non_null');
 ```
 
-Under `last_non_null` mode, the table merges rows with the same primary key and timestamp by keeping the latest value of each field.
+Under `last_non_null` mode, the table merges rows with the same primary key and timestamp by keeping the latest non-null value of each field.
 ```sql
 INSERT INTO metrics VALUES ('host1', 0, 0, NULL), ('host2', 1, NULL, 1);
 INSERT INTO metrics VALUES ('host1', 0, NULL, 10), ('host2', 1, 11, NULL);

docs/user-guide/manage-data/overview.md

@@ -177,7 +177,7 @@ That will not update anything:
 +-----------+---------------------+------+--------+
 ```
 
-For more information about the `merge_mode` option, please refer to the [CREATE TABLE](/reference/sql/create.md##create-a-table-with-merge-mode) statement.
+For more information about the `merge_mode` option, please refer to the [CREATE TABLE](/reference/sql/create.md#create-a-table-with-merge-mode) statement.
 
 ### Avoid updating data by creating table with `append_mode` option
 
@@ -294,7 +294,7 @@ You can use Time to Live (TTL) policies to automatically remove stale data from
 - Decrease storage costs by cleaning out obsolete data.
 - Reduce the number of rows the database has to scan for some queries, potentially increasing query performance.
 
-> Please note that the expired data due to TTL policy may not be deleted right after the expiration time. Instead, they are deleted during the compaction, which is a background job ran asynchronously.
+> Please note that the expired data due to TTL policy may not be deleted right after the expiration time. Instead, they are deleted during the compaction, which is a background job run asynchronously.
 > If you are testing the TTL policy, be sure to trigger data flush and compaction before querying the data.
 > You can use our "[ADMIN](/reference/sql/admin.md)" functions to manually run them.
 
@@ -323,6 +323,15 @@ Otherwise, the database TTL policy will be applied to the table.
 
 The value of `'ttl'` can be one of duration (like `1hour 12min 5s`), `instant` or `forever`. See details in [CREATE](/reference/sql/create.md#create-a-table-with-ttl) statement.
 
+Use [`ALTER`](/reference/sql/alter.md#alter-table-options) to modify the TTL of an existing table or database:
+
+```sql
+-- for table
+ALTER TABLE monitor SET 'ttl'='1 month';
+-- for database
+ALTER DATABASE test SET 'ttl'='1 month';
+```
+
 If you want to remove the TTL policy, you can use the following SQL
 
 ```sql

i18n/zh/docusaurus-plugin-content-docs/current/reference/sql/create.md

@@ -265,7 +265,7 @@ create table if not exists metrics(
 with('merge_mode'='last_non_null');
 ```
 
-在 `last_non_null` 模式下，表会通过保留每个字段的最新值来合并具有相同主键和时间戳的行。
+在 `last_non_null` 模式下，表会通过保留每个字段的最新非 NULL 值来合并具有相同主键和时间戳的行。
 
 ```sql
 INSERT INTO metrics VALUES ('host1', 0, 0, NULL), ('host2', 1, NULL, 1);

i18n/zh/docusaurus-plugin-content-docs/current/user-guide/manage-data/overview.md

@@ -174,7 +174,7 @@ VALUES ("127.0.0.1", "2024-07-11 20:00:01", NULL);
 +-----------+---------------------+------+--------+
 ```
 
-有关 `merge_mode` 选项的更多信息，请参阅 [CREATE TABLE](/reference/sql/create.md##创建带有-merge-模式的表) 语句。
+有关 `merge_mode` 选项的更多信息，请参阅 [CREATE TABLE](/reference/sql/create.md#创建带有-merge-模式的表) 语句。
 
 ### 通过创建带有 `append_mode` 选项的表来避免更新数据
 
@@ -319,7 +319,16 @@ CREATE DATABASE test WITH ('ttl'='7d');
 如果 table 有自己的 TTL 策略，则该策略将优先于 database 的 TTL 策略，
 否则 database 的 TTL 策略将被应用于 table。
 
-`'ttl'` 参数的值可以是持续时间（例如 `1hour 12min 5s`）、`instant` 或 `forever`。有关详细信息，请参阅 [CREATE](/reference/sql/create.md#create-a-table-with-ttl) 语句的文档。
+`'ttl'` 参数的值可以是持续时间（例如 `1hour 12min 5s`）、`instant` 或 `forever`。有关详细信息，请参阅 [CREATE](/reference/sql/create.md#创建指定-ttl-的表) 语句的文档。
+
+使用 [`ALTER`](/reference/sql/alter.md#修改表的参数) 来修改现有表或数据库的 TTL：
+
+```sql
+-- 针对表
+ALTER TABLE monitor SET 'ttl'='1 month';
+-- 针对数据库
+ALTER DATABASE test SET 'ttl'='1 month';
+```
 
 如果你想移除 TTL 策略，可以使用如下 SQL 语句：
 

i18n/zh/docusaurus-plugin-content-docs/version-0.17/reference/sql/create.md

@@ -265,7 +265,7 @@ create table if not exists metrics(
 with('merge_mode'='last_non_null');
 ```
 
-在 `last_non_null` 模式下，表会通过保留每个字段的最新值来合并具有相同主键和时间戳的行。
+在 `last_non_null` 模式下，表会通过保留每个字段的最新非 NULL 值来合并具有相同主键和时间戳的行。
 
 ```sql
 INSERT INTO metrics VALUES ('host1', 0, 0, NULL), ('host2', 1, NULL, 1);

i18n/zh/docusaurus-plugin-content-docs/version-0.17/user-guide/manage-data/overview.md

@@ -174,7 +174,7 @@ VALUES ("127.0.0.1", "2024-07-11 20:00:01", NULL);
 +-----------+---------------------+------+--------+
 ```
 
-有关 `merge_mode` 选项的更多信息，请参阅 [CREATE TABLE](/reference/sql/create.md##创建带有-merge-模式的表) 语句。
+有关 `merge_mode` 选项的更多信息，请参阅 [CREATE TABLE](/reference/sql/create.md#创建带有-merge-模式的表) 语句。
 
 ### 通过创建带有 `append_mode` 选项的表来避免更新数据
 
@@ -291,6 +291,10 @@ Time to Live (TTL) 允许你设置定期删除表中数据的策略，
 - 通过清理过期数据来降低存储成本。
 - 减少数据库在某些查询中需要扫描的行数，从而提高查询性能。
 
+> 请注意，因 TTL 策略而过期的数据，并不是在 TTL 到期时立刻删除的，而是发生在 compaction 时。compaction 是一个后台任务。
+> 如果你在测试 TTL 策略，查询过期数据之前请确保 flush 和 compaction 都已触发过了。
+> 你可以使用我们的 ”[ADMIN](/reference/sql/admin.md)“ 函数来手动触发。
+
 你可以在创建每个表时设置 TTL。
 例如，以下 SQL 语句创建了一个名为 `monitor` 的表，并设置了 7 天的 TTL 策略：
 
@@ -315,7 +319,16 @@ CREATE DATABASE test WITH ('ttl'='7d');
 如果 table 有自己的 TTL 策略，则该策略将优先于 database 的 TTL 策略，
 否则 database 的 TTL 策略将被应用于 table。
 
-`'ttl'` 参数的值可以是持续时间（例如 `1hour 12min 5s`）、`instant` 或 `forever`。有关详细信息，请参阅 [CREATE](/reference/sql/create.md#create-a-table-with-ttl) 语句的文档。
+`'ttl'` 参数的值可以是持续时间（例如 `1hour 12min 5s`）、`instant` 或 `forever`。有关详细信息，请参阅 [CREATE](/reference/sql/create.md#创建指定-ttl-的表) 语句的文档。
+
+使用 [`ALTER`](/reference/sql/alter.md#修改表的参数) 来修改现有表或数据库的 TTL：
+
+```sql
+-- 针对表
+ALTER TABLE monitor SET 'ttl'='1 month';
+-- 针对数据库
+ALTER DATABASE test SET 'ttl'='1 month';
+```
 
 如果你想移除 TTL 策略，可以使用如下 SQL 语句：
 

versioned_docs/version-0.17/reference/sql/create.md

@@ -261,7 +261,7 @@ create table if not exists metrics(
 with('merge_mode'='last_non_null');
 ```
 
-Under `last_non_null` mode, the table merges rows with the same primary key and timestamp by keeping the latest value of each field.
+Under `last_non_null` mode, the table merges rows with the same primary key and timestamp by keeping the latest non-null value of each field.
 ```sql
 INSERT INTO metrics VALUES ('host1', 0, 0, NULL), ('host2', 1, NULL, 1);
 INSERT INTO metrics VALUES ('host1', 0, NULL, 10), ('host2', 1, 11, NULL);

versioned_docs/version-0.17/user-guide/manage-data/overview.md

@@ -177,7 +177,7 @@ That will not update anything:
 +-----------+---------------------+------+--------+
 ```
 
-For more information about the `merge_mode` option, please refer to the [CREATE TABLE](/reference/sql/create.md##create-a-table-with-merge-mode) statement.
+For more information about the `merge_mode` option, please refer to the [CREATE TABLE](/reference/sql/create.md#create-a-table-with-merge-mode) statement.
 
 ### Avoid updating data by creating table with `append_mode` option
 
@@ -294,6 +294,10 @@ You can use Time to Live (TTL) policies to automatically remove stale data from
 - Decrease storage costs by cleaning out obsolete data.
 - Reduce the number of rows the database has to scan for some queries, potentially increasing query performance.
 
+> Please note that the expired data due to TTL policy may not be deleted right after the expiration time. Instead, they are deleted during the compaction, which is a background job run asynchronously.
+> If you are testing the TTL policy, be sure to trigger data flush and compaction before querying the data.
+> You can use our "[ADMIN](/reference/sql/admin.md)" functions to manually run them.
+
 You can set TTL for every table when creating it. For example, the following SQL statement creates a table named `monitor` with a TTL policy of 7 days:
 
 ```sql
@@ -319,6 +323,15 @@ Otherwise, the database TTL policy will be applied to the table.
 
 The value of `'ttl'` can be one of duration (like `1hour 12min 5s`), `instant` or `forever`. See details in [CREATE](/reference/sql/create.md#create-a-table-with-ttl) statement.
 
+Use [`ALTER`](/reference/sql/alter.md#alter-table-options) to modify the TTL of an existing table or database:
+
+```sql
+-- for table
+ALTER TABLE monitor SET 'ttl'='1 month';
+-- for database
+ALTER DATABASE test SET 'ttl'='1 month';
+```
+
 If you want to remove the TTL policy, you can use the following SQL
 
 ```sql