Using a SELECT alias inside HAVING

asked 8 hours ago by @qa-l59utglddsh2xxljzdix 0 rep · 62 views

I'm using Apache IoTDB 2.0.8 in table model. I need to filter grouped aggregate results, so I tried to define AVG(voltage) once with the alias avg_v and reuse that alias in HAVING.

Schema and original data:

CREATE TABLE voltage_log (device_id STRING TAG, region STRING TAG, voltage DOUBLE FIELD);
INSERT INTO voltage_log(`time`, device_id, region, voltage) VALUES (1000, 'D1', 'north', 220.0);
INSERT INTO voltage_log(`time`, device_id, region, voltage) VALUES (2000, 'D2', 'north', 225.0);
INSERT INTO voltage_log(`time`, device_id, region, voltage) VALUES (3000, 'D3', 'south', 198.0);
INSERT INTO voltage_log(`time`, device_id, region, voltage) VALUES (4000, 'D4', 'south', 202.0);

Failed attempt: reference the SELECT alias inside HAVING:

SELECT region, AVG(voltage) AS avg_v 
FROM voltage_log 
`GROUP BY` region 
HAVING avg_v > 210;

Actual result:

Msg: org.apache.iotdb.jdbc.IoTDBSQLException: 616: Column 'avg_v' cannot be resolved

What I have already tried: repeat the aggregate expression inside HAVING:

SELECT region, AVG(voltage) AS avg_v 
FROM voltage_log 
`GROUP BY` region 
HAVING AVG(voltage) > 210;

Comparison result:

  +------+-----+
  |region|avg_v|
  +------+-----+
  | north|222.5|
  +------+-----+

My question:

In IoTDB table model, are SELECT aliases intentionally unavailable inside HAVING, and is repeating the aggregate expression the expected way to write this?

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The logical order of execution of the different clauses of the SELECT statement is not the same as the order in which the clauses were written.

+-------------+-------------------------------+
| SQL CLAUSE  | WRITTEN ORDER | LOGICAL ORDER |
+---------------------------------------------+
| SELECT      | 1             | 6             |
+---------------------------------------------+
| FROM        | 2             | 1             |
+---------------------------------------------+
| WHERE       | 3             | 2             |
+------------------------------------_--------+
| GROUP BY    | 4             | 3             |
+---------------------------------------------+
| HAVING      | 5             | 4             |
+---------------------------------------------+
| WINDOW      | 6             | 5             |
+---------------------------------------------+
| ORDER BY    | 7             | 7             |
+---------------------------------------------+

Thus, an alias defined at the SELECT level can only be visible to the ORDER BY clause and no other...

Avery Hayes · 0 rep · 8 hours ago

Using a SELECT alias inside HAVING

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