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# 常见函数

## 1.`GROUP BY`分组查询

### 1.1分组前的筛选

where 语句放在group by 语句前

```sql
SELECT 
  AVG(id),
  orderid 
FROM
  `pmw_goodstype` 
GROUP BY orderid ;
```

### 1.2分组后的筛选

`HAVING`关键字