HAVING Clause

1. Syntax Overview

HAVING booleanExpression

1.1 HAVING Clause

The HAVING clause is used to filter aggregated results after a GROUP BY operation has been applied.

Notes

In terms of syntax, the HAVING clause is similar to the WHERE clause. However, while WHERE filters rows before grouping and aggregation, HAVING filters the results after grouping and aggregation.

2. Sample Data and Usage Examples

The Example Data pagepage provides SQL statements to construct table schemas and insert data. By downloading and executing these statements in the IoTDB CLI, you can import the data into IoTDB. This data can be used to test and run the example SQL queries included in this documentation, allowing you to reproduce the described results.

Example 1: Filtering Devices with Entry Counts Below a Certain Threshold

This query calculates the number of entries (COUNT(*)) for each device_id in the table1 table and filters out devices with a count less than 5.

SELECT device_id, COUNT(*)
  FROM table1
  GROUP BY device_id
  HAVING COUNT(*) >= 5;

Result:

+---------+-----+
|device_id|_col1|
+---------+-----+
|      100|    8|
|      101|   10|
+---------+-----+
Total line number = 2
It costs 0.063s

Example 2: Calculating Hourly Average Temperatures and Filtering Results

This query calculates the hourly average temperature (AVG(temperature)) for each device in the table1 table and filters out those with an average temperature below 85.0.

SELECT date_bin(1h, time) as hour_time, device_id, AVG(temperature) as avg_temp
  FROM table1
  GROUP BY date_bin(1h, time), device_id
  HAVING AVG(temperature) >= 85.0;

Result:

+-----------------------------+---------+--------+
|                    hour_time|device_id|avg_temp|
+-----------------------------+---------+--------+
|2024-11-29T18:00:00.000+08:00|      100|    90.0|
|2024-11-28T08:00:00.000+08:00|      100|    85.0|
|2024-11-28T10:00:00.000+08:00|      100|    85.0|
|2024-11-28T11:00:00.000+08:00|      100|    88.0|
|2024-11-26T13:00:00.000+08:00|      100|    90.0|
|2024-11-30T09:00:00.000+08:00|      101|    90.0|
|2024-11-30T14:00:00.000+08:00|      101|    90.0|
|2024-11-29T10:00:00.000+08:00|      101|    85.0|
|2024-11-27T16:00:00.000+08:00|      101|    85.0|
+-----------------------------+---------+--------+
Total line number = 9
It costs 0.079s