druid sql part-1
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> [!WARNING]
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> Apache Druid支持两种查询语言: Druid SQL和 [原生查询](makeNativeQueries.md)。本文档讲述SQL查询。
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Druid SQL是一个内置的SQL层,是Druid基于JSON的本地查询语言的替代品,它由基于 [Apache Calcite](https://calcite.apache.org/) 的解析器和规划器提供支持。Druid SQL将SQL转换为查询Broker(查询的第一个进程)上的原生Druid查询,然后作为原生Druid查询传递给数据进程。除了在Broker上 [转换SQL](查询翻译) 的(轻微)开销之外,与原生查询相比,没有额外的性能损失。
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### 查询符号
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Druid SQL支持如下结构的SELECT查询:
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```
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[ EXPLAIN PLAN FOR ]
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[ WITH tableName [ ( column1, column2, ... ) ] AS ( query ) ]
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SELECT [ ALL | DISTINCT ] { * | exprs }
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FROM { <table> | (<subquery>) | <o1> [ INNER | LEFT ] JOIN <o2> ON condition }
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[ WHERE expr ]
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[ GROUP BY [ exprs | GROUPING SETS ( (exprs), ... ) | ROLLUP (exprs) | CUBE (exprs) ] ]
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[ HAVING expr ]
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[ ORDER BY expr [ ASC | DESC ], expr [ ASC | DESC ], ... ]
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[ LIMIT limit ]
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[ UNION ALL <another query> ]
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```
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#### FROM
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#### WHERE
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#### GROUP BY
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