Skip to main content

FROM & JOIN Clause

January 3, 2025About 8 min

FROM & JOIN Clause

1 Syntax Overview

FROM relation (',' relation)*

relation
    : relation joinType JOIN relation joinCriteria 
    | aliasedRelation
    ;

joinType
    : INNER?
    | FULL OUTER?
    ;

joinCriteria
    : ON booleanExpression
    | USING '(' identifier (',' identifier)* ')'
    ;

aliasedRelation
    : relationPrimary (AS? identifier columnAliases?)?
    ;

columnAliases
    : '(' identifier (',' identifier)* ')'
    ;

relationPrimary
    : qualifiedName                                              #tableName
    | '(' query ')'                                              #subqueryRelation
    | '(' relation ')'                                           #parenthesizedRelation
    ;

qualifiedName
    : identifier ('.' identifier)*
    ;

2 FROM Clause Syntax

The FROM clause specifies the data sources for the query. Logically, query execution begins with the FROM clause. It can include a single table, a combination of multiple tables joined using JOIN clauses, or a subquery containing another SELECT query.

3 JOIN Clause

The JOIN clause combines two tables based on specific conditions, typically predicates, but other implicit rules can also apply.

In the current version of IoTDB, the following joins are supported:

  1. Inner Join: Combines rows that meet the join condition, effectively returning the intersection of the two tables.
  2. Full Outer Join: Returns all records from both tables, inserting NULL values for unmatched rows.

Note: The join condition in IoTDB must be an equality condition on the time column. This restriction ensures that rows are joined based on the equality of their timestamps.

3.1 Inner Join

INNER JOIN can be written explicitly or implicitly by omitting the INNER keyword. It returns records where the join condition is satisfied.

3.1.1 Explicit Join (Recommended)

Explicit joins use the syntax JOIN + ON or JOIN + USING to specify join conditions.

The SQL syntax is as follows:

// Explicit join: Specify the join condition after the ON keyword or the join column(s) after the USING keyword.
SELECT selectExpr [, selectExpr] ... FROM <TABLE_NAME> [INNER] JOIN <TABLE_NAME> joinCriteria [WHERE whereCondition]

joinCriteria
    : ON booleanExpression
    | USING '(' identifier (',' identifier)* ')'
    ;

Note: Difference Between USING and ON

  • USING simplifies explicit join conditions by accepting a list of column names common to both tables. For example, USING (time) is equivalent to ON (t1.time = t2.time). When using USING, there is logically one time column in the result.
  • With ON, column names remain distinct (e.g., t1.time and t2.time).
  • The final query result depends on the fields specified in the SELECT statement.

3.1.2 Implicit Join

Implicit joins do not use JOIN, ON, or USING keywords. Instead, conditions are specified in the WHERE clause:

The SQL syntax is as follows:

// Implicit join: Specify the join condition in the WHERE clause.
SELECT selectExpr [, selectExpr] ... FROM <TABLE_NAME> [, <TABLE_NAME>] ... [WHERE whereCondition]

3.2 Outer Join

An outer join returns rows even when no matching records exist in the other table. Types include:

  • LEFT OUTER JOIN: Returns all rows from the left table.
  • RIGHT OUTER JOIN: Returns all rows from the right table.
  • FULL OUTER JOIN: Returns all rows from both tables.

IoTDB currently supports only FULL [OUTER] JOIN. This type returns all records from both tables. If a record in one table has no match in the other, NULL values are returned for the unmatched fields. FULL JOIN must use explicit join conditions.

4 Example Queries

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.corresponding results.

4.1 FROM Examples

4.1.1 Query from a Single Table

Example 1: This query retrieves all records from table1 and sorts them by time.

SELECT * FROM table1 ORDER BY time;

Query Results:

+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                arrival_time|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-26T13:37:00.000+08:00|  北京|    1001|      100|       A|        180|       90.0|    35.1|  true|2024-11-26T13:37:34.000+08:00|
|2024-11-26T13:38:00.000+08:00|  北京|    1001|      100|       A|        180|       90.0|    35.1|  true|2024-11-26T13:38:25.000+08:00|
|2024-11-27T16:38:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    35.1|  true|2024-11-27T16:37:01.000+08:00|
|2024-11-27T16:39:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    35.3|  null|                         null|
|2024-11-27T16:40:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-27T16:37:03.000+08:00|
|2024-11-27T16:41:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-27T16:37:04.000+08:00|
|2024-11-27T16:42:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    35.2| false|                         null|
|2024-11-27T16:43:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    null| false|                         null|
|2024-11-27T16:44:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    null| false|2024-11-27T16:37:08.000+08:00|
|2024-11-28T08:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    null|  null|2024-11-28T08:00:09.000+08:00|
|2024-11-28T09:00:00.000+08:00|  上海|    3001|      100|       C|         90|       null|    40.9|  true|                         null|
|2024-11-28T10:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    35.2|  null|2024-11-28T10:00:11.000+08:00|
|2024-11-28T11:00:00.000+08:00|  上海|    3001|      100|       C|         90|       88.0|    45.1|  true|2024-11-28T11:00:12.000+08:00|
|2024-11-29T10:00:00.000+08:00|  上海|    3001|      101|       D|        360|       85.0|    null|  null|2024-11-29T10:00:13.000+08:00|
|2024-11-29T11:00:00.000+08:00|  上海|    3002|      100|       E|        180|       null|    45.1|  true|                         null|
|2024-11-29T18:30:00.000+08:00|  上海|    3002|      100|       E|        180|       90.0|    35.4|  true|2024-11-29T18:30:15.000+08:00|
|2024-11-30T09:30:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-30T14:30:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 18
It costs 0.085s

Example 2: This query retrieves all records from table1 where the device is 101 and sorts them by time.

SELECT * FROM table1 t1 where t1.device_id='101' order by time;

Query Results:

+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                arrival_time|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-27T16:38:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    35.1|  true|2024-11-27T16:37:01.000+08:00|
|2024-11-27T16:39:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    35.3|  null|                         null|
|2024-11-27T16:40:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-27T16:37:03.000+08:00|
|2024-11-27T16:41:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-27T16:37:04.000+08:00|
|2024-11-27T16:42:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    35.2| false|                         null|
|2024-11-27T16:43:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    null| false|                         null|
|2024-11-27T16:44:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    null| false|2024-11-27T16:37:08.000+08:00|
|2024-11-29T10:00:00.000+08:00|  上海|    3001|      101|       D|        360|       85.0|    null|  null|2024-11-29T10:00:13.000+08:00|
|2024-11-30T09:30:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-30T14:30:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 10
It costs 0.061s

4.1.2 Querying from a Subquery

Example 1: This query retrieves the total number of records in table1.

SELECT COUNT(*) AS count FROM (SELECT * FROM table1);

Query Results:

+-----+
|count|
+-----+
|   18|
+-----+
Total line number = 1
It costs 0.072s

4.2 JOIN Examples

4.2.1 Inner Join

Example 1: Explicit Join using ON This query retrieves records where table1 and table2 share the same time values.

SELECT 
  t1.time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2 
FROM 
  table1 t1 JOIN table2 t2 
ON t1.time = t2.time

Query Results:

+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 3
It costs 0.076s

Example 2: Explicit Join using USING This query retrieves records from table1 and table2, joining on the time column.

SELECT time,
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2   
FROM 
  table1 t1 JOIN table2 t2
USING(time)

Query Results:

+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 3
It costs 0.081s

Example 3: Implicit Join using WHERE This query joins table1 and table2 by specifying the condition in the WHERE clause.

SELECT t1.time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2 
FROM 
table1 t1, table2 t2
WHERE
t1.time=t2.time

Query Results:

+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 3
It costs 0.082s

4.2.2 Outer Join

Example 1: Full Outer Join using ON This query retrieves all records from table1 and table2, including unmatched rows with NULL values.

SELECT 
  t1.time as time1, t2.time as time2, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2  
FROM 
  table1 t1 FULL JOIN table2 t2 
ON t1.time = t2.time

Query Results:

+-----------------------------+-----------------------------+-------+------------+-------+------------+
|                        time1|                        time2|device1|temperature1|device2|temperature2|
+-----------------------------+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-26T13:38:00.000+08:00|                         null|    100|        90.0|   null|        null|
|                         null|2024-11-27T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-27T16:38:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:39:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:40:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:41:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:42:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:43:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:44:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-28T08:00:00.000+08:00|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-28T09:00:00.000+08:00|                         null|    100|        null|   null|        null|
|2024-11-28T10:00:00.000+08:00|                         null|    100|        85.0|   null|        null|
|2024-11-28T11:00:00.000+08:00|                         null|    100|        88.0|   null|        null|
|                         null|2024-11-29T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-29T10:00:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-29T11:00:00.000+08:00|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
|2024-11-29T18:30:00.000+08:00|                         null|    100|        90.0|   null|        null|
|                         null|2024-11-30T00:00:00.000+08:00|   null|        null|    101|        90.0|
|2024-11-30T09:30:00.000+08:00|                         null|    101|        90.0|   null|        null|
|2024-11-30T14:30:00.000+08:00|                         null|    101|        90.0|   null|        null|
+-----------------------------+-----------------------------+-------+------------+-------+------------+
Total line number = 21
It costs 0.071s

Example 2: Explicit Join using USING

This query retrieves all records from table1 and table2, combining them based on the time column. Rows with no matches in one of the tables will include NULL values for the missing fields.

SELECT 
  time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2  
FROM 
  table1 t1 FULL JOIN table2 t2 
USING(time)

Query Results:

+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-26T13:38:00.000+08:00|    100|        90.0|   null|        null|
|2024-11-27T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-27T16:38:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:39:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:40:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:41:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:42:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:43:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:44:00.000+08:00|    101|        null|   null|        null|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-28T09:00:00.000+08:00|    100|        null|   null|        null|
|2024-11-28T10:00:00.000+08:00|    100|        85.0|   null|        null|
|2024-11-28T11:00:00.000+08:00|    100|        88.0|   null|        null|
|2024-11-29T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-29T10:00:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
|2024-11-29T18:30:00.000+08:00|    100|        90.0|   null|        null|
|2024-11-30T00:00:00.000+08:00|   null|        null|    101|        90.0|
|2024-11-30T09:30:00.000+08:00|    101|        90.0|   null|        null|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|   null|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 21
It costs 0.073s

Copyright © 2025 The Apache Software Foundation. Apache IoTDB, IoTDB, Apache, the Apache feather logo, and the Apache IoTDB project logo are either registered trademarks or trademarks of The Apache Software Foundation in all countries

Having questions? Connect with us on QQ, WeChat, or Slack. Join the community