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| # 结果集空值过滤 |
| |
| 在 IoTDB 中，可以使用 `WITHOUT NULL` 子句对结果集中的空值进行过滤，有两种过滤策略： |
| |
| 1. 如果结果集中，任意一列为 null，则过滤掉该行；即获得的结果集不包含任何空值。 |
| |
| ```sql |
| select * from root.ln.** where time <= 2017-11-01T00:01:00 WITHOUT NULL ANY |
| ``` |
| |
| 2. 在降采样查询中，如果结果集的某一行所有列都为 null，则过滤掉该行；即获得的结果集不包含所有值都为 null 的行。 |
| |
| ```sql |
| select * from root.ln.** where time <= 2017-11-01T00:01:00 WITHOUT NULL ALL |
| ``` |
