Source: https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/dql/composite-query/
Documentation version: v5.3.2

# Composite query statement

The composite query statement combines the result sets of multiple linear query statements.

## Limitations

The linear query statements to be combined must meet the following limitations:

- The result sets that are passed to linear query statements must be of the same data types.
- 

The result sets (for example, A and B) of the linear query statements must be column name-equal and column combinable, that is, the following conditions must be met:

  - The result sets A and B have the same number of columns.
  - For each column from the result set A, there is a column of the same name from the result set B, and vice versa.
  - The ordering of the columns from result sets A and B is the same.
  - For every pair of columns from result sets A and B, the data types of these columns are comparable. For more information, see [Comparison predicate](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/fe/predicates/comparison/).

## Syntax

diagramsource

 composite_query_statement query_conjunction  

````
composite_query_statement ::=
  linear_query_statement query_conjunction linear_query_statement ( query_conjunction linear_query_statement )*

query_conjunction ::=
  'UNION' ('DISTINCT' | 'ALL')? 
  | 'EXCEPT' ('DISTINCT' | 'ALL')? 
  | 'INTERSECT' ('DISTINCT' | 'ALL')? 

````

## Parameters

### `UNION | EXCEPT | INTERSECT`

Specifies the set operator to be used when combining the result sets of two queries.

- `UNION`: This operator combines all rows in the result sets of two queries into a single result set.
- `EXCEPT`: This operator returns only the rows from the first result set that are not in the second result set.
- `INTERSECT`: This operator returns only the rows that are in both result sets.

### `DISTINCT | ALL`

Specifies whether to remove duplicate rows from the result set.

- `DISTINCT`: Default value, removes duplicate rows from the result set.
- `ALL`: Retains all rows in the result set, including duplicates.

### `linear_query_statement`

Specifies a linear composition of simple query statements. For more information, see [Linear query statement](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/dql/linear-query/).

## Examples

### Combine two queries using the `UNION DISTINCT` operator

````
'''
FOR i IN LIST[4,1,2,3,3] RETURN i  
UNION DISTINCT 
FOR i IN LIST[11,2,2,22,33,33] RETURN i ORDER BY i OFFSET 1 LIMIT 2
'''

````

Return:

````
+----+
| i  |
+----+
| 4  |
| 1  |
| 2  |
| 3  |
| 11 |
+----+

````

### Combine two queries using the `UNION ALL` operator

````
'''
FOR i IN LIST[4,1,2,3,3] RETURN i 
UNION ALL 
FOR i IN LIST[11,2,2,22,33,33] RETURN i ORDER BY i OFFSET 1 LIMIT 2
'''

````

Return:

````
+----+
| i  |
+----+
| 4  |
| 1  |
| 2  |
| 3  |
| 3  |
| 2  |
| 11 |
+----+

````

### Combine two queries using the `EXCEPT DISTINCT` operator

````
'''
FOR i IN LIST[1,2,3,4] RETURN i AS num
EXCEPT DISTINCT 
FOR i IN LIST[2,4] RETURN i AS num
ORDER BY num
'''

````

Return:

````
+-----+
| num |
+-----+
| 1   |
| 3   |
+-----+

````

### Combine two queries using the `EXCEPT ALL` operator

````
'''
FOR i IN LIST[4,1,2,3,2,3] RETURN i 
EXCEPT ALL 
FOR i IN LIST[11,2,2,22,33,33] RETURN i ORDER BY i OFFSET 1 LIMIT 2
'''

````

Return:

````
+---+
| i |
+---+
| 4 |
| 1 |
| 3 |
| 3 |
+---+

````

### Combine two queries using the `INTERSECT DISTINCT` operator

````
'''
FOR i IN LIST[1,2,3,4] RETURN i AS num
INTERSECT DISTINCT 
FOR i IN LIST[3,4,5] RETURN i AS num
ORDER BY num
'''

````

Return:

````
+-----+
| num |
+-----+
| 3   |
| 4   |
+-----+

````

### Combine two queries using the `INTERSECT ALL` operator

````
'''
FOR i IN LIST[4,1,2,3,2,3] RETURN i 
INTERSECT ALL 
FOR i IN LIST[11,2,2,22,33,33] RETURN i ORDER BY i OFFSET 1 LIMIT 2
'''

````

Return:

````
+---+
| i |
+---+
| 2 |
| 2 |
+---+

````