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| |
| # 概览 |
| |
| ## 1. 语法概览 |
| |
| ```SQL |
| SELECT ⟨select_list⟩ |
| FROM ⟨tables⟩ |
| [WHERE ⟨condition⟩] |
| [GROUP BY ⟨groups⟩] |
| [HAVING ⟨group_filter⟩] |
| [FILL ⟨fill_methods⟩] |
| [ORDER BY ⟨order_expression⟩] |
| [OFFSET ⟨n⟩] |
| [LIMIT ⟨n⟩]; |
| ``` |
| |
| IoTDB 查询语法提供以下子句： |
| |
| - SELECT 子句：查询结果应包含的列。详细语法见：[SELECT子句](../SQL-Manual/Select-Clause.md) |
| - FROM 子句：指出查询的数据源，可以是单个表、多个通过 `JOIN` 子句连接的表，或者是一个子查询。详细语法见：[FROM & JOIN 子句](../SQL-Manual/From-Join-Clause.md) |
| - WHERE 子句：用于过滤数据，只选择满足特定条件的数据行。这个子句在逻辑上紧跟在 FROM 子句之后执行。详细语法见：[WHERE 子句](../SQL-Manual/Where-Clause.md) |
| - GROUP BY 子句：当需要对数据进行聚合时使用，指定了用于分组的列。详细语法见：[GROUP BY 子句](../SQL-Manual/GroupBy-Clause.md) |
| - HAVING 子句：在 GROUP BY 子句之后使用，用于对已经分组的数据进行过滤。与 WHERE 子句类似，但 HAVING 子句在分组后执行。详细语法见：[HAVING 子句](../SQL-Manual/Having-Clause.md) |
| - FILL 子句：用于处理查询结果中的空值，用户可以使用 FILL 子句来指定数据缺失时的填充模式（如前一个非空值或线性插值）来填充 null 值，以便于数据可视化和分析。 详细语法见：[FILL 子句](../SQL-Manual/Fill-Clause.md) |
| - ORDER BY 子句：对查询结果进行排序，可以指定升序（ASC）或降序（DESC），以及 NULL 值的处理方式（NULLS FIRST 或 NULLS LAST）。详细语法见：[ORDER BY 子句](../SQL-Manual/OrderBy-Clause.md) |
| - OFFSET 子句：用于指定查询结果的起始位置，即跳过前 OFFSET 行。与 LIMIT 子句配合使用。详细语法见：[LIMIT 和 OFFSET 子句](../SQL-Manual/Limit-Offset-Clause.md) |
| - LIMIT 子句：限制查询结果的行数，通常与 OFFSET 子句一起使用以实现分页功能。详细语法见：[LIMIT 和 OFFSET 子句](../SQL-Manual/Limit-Offset-Clause.md) |
| |
| ## 2. 子句执行顺序 |
| |
| |
|  |
