* 用例1：查询特定日期区间内的主力合约信息
```
import dai
df = dai.query("""
SELECT
date, dominant, instrument, product_code
FROM cn_future_dominant
ORDER BY date""",
filters={"date": ["2023-01-01", "2023-01-31"]}
).df()
```
* 用例2：查询指定期间内的品种代码对应的主力合约变化
```
import dai
df = dai.query("""
SELECT
date, product_code, dominant
FROM cn_future_dominant
WHERE product_code = 'AP'
ORDER BY date""",
filters={"date": ["2023-01-01", "2023-12-31"]}
).df()
```
* 用例3：联结期货日行情数据表，以获取主力合约的交易量信息
```
import dai
df = dai.query("""
SELECT
a.date, a.instrument, a.dominant, b.volume
FROM cn_future_dominant AS a
JOIN cn_future_bar1d AS b
USING(instrument, date)
WHERE a.product_code = 'AP'
ORDER BY date""",
filters={"date": ["2023-01-01", "2023-12-31"]}
).df()
```