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# 10.Select DISTINCT

可以使用DISTINCT关键字来消除重复文档的输出。

Query：

```sql
SELECT DISTINCT orderlines[0].productId
    FROM orders
```

结果

```javascript
{
  "results": [
    {
      "productId": "coffee01"
    },
    {
      "productId": "tea111"
    }
  ]
}
```

对比查询

```sql
SELECT  orderlines[0].productId
    FROM orders
```

结果：

```javascript
{
  "results": [
    {
      "productId": "coffee01"
    },
    {
      "productId": "coffee01"
    },
    {
      "productId": "tea111"
    },
    {
      "productId": "coffee01"
    }
  ]
}
```