集合操作（UNION，INTERSECT， MINUS）Graph
您可以使用集合运算符 UNION、UNION ALL、INTERSECT 和 MINUS 进行多个组合查询。所有集合运算符具有相同的优先级。如果 nGQL 语句包含多个集合运算符，则 NebulaGraph 将对其进行从左到右处理，除非使用括号明确指定了顺序。
复合查询中，GO 语句返回的结果必须列数相同，且数据类型相同（比如均为数字类型或字符类型）。
UNION，UNION DISTINCT，UNION ALLGraph
UNION DISTINCT（简称 UNION）返回数据集 A 和 B 的并集（不包含重复元素）。
UNION ALL 返回数据集 A 和 B 的并集（包含重复元素）。UNION 语法为
<left> UNION [DISTINCT | ALL] <right> [ UNION [DISTINCT | ALL] <right> ...]
<left> 和 <right> 必须列数相同，且数据类型相同。如果数据类型不同，将按照Graph进行转换。
示例Graph
nebula> GO FROM 1 OVER e1 \
UNION \
GO FROM 2 OVER e1;
以上语句返回点 1 和 2（沿边 e1）关联的唯一的点。
nebula> GO FROM 1 OVER e1 \
UNION ALL\
GO FROM 2 OVER e1;
以上语句返回点 1 和 2 关联的所有点，其中存在重复点。
UNION 亦可与 YIELD 同时使用，例如以下语句：
nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2; -- query 1
=======================
| id | col_1| col_2 |
=======================
| 104 | 1 | 2 | -- line 1
-----------------------
| 215 | 4 | 3 | -- line 3
-----------------------
nebula> GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2; -- query 2
======================
| id | col_1| col_2 |
======================
| 104 | 1 | 2 | -- line 1
----------------------
| 104 | 2 | 2 | -- line 2
----------------------
nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2 \
UNION /* DISTINCT */ \
GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2;
以上语句返回
=======================
| id | col_1| col_2 | -- UNION or UNION DISTINCT. The column names come from query 1
=======================
| 104 | 1 | 2 | -- line 1
-----------------------
| 104 | 2 | 2 | -- line 2
-----------------------
| 215 | 4 | 3 | -- line 3
-----------------------
请注意第一行与第二行返回相同 id 的点，但是返回的值不同。DISTINCT 检查返回结果中的重复值。所以第一行与第二行的返回结果不同。
UNION ALL 返回结果为
nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2 \
UNION ALL \
GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2;
======================
| id | col_1| col_2 | -- UNION ALL
======================
| 104 | 1 | 2 | -- line 1
----------------------
| 104 | 1 | 2 | -- line 1
----------------------
| 104 | 2 | 2 | -- line 2
----------------------
| 215 | 4 | 3 | -- line 3
----------------------
INTERSECTGraph
INTERSECT 返回集合 A 和 B 的交集（A ⋂ B）。
<left> INTERSECT <right>
与 UNION 类似， <left> 和 <right> 必须列数相同，且数据类型相同。
此外，只返回 <left> 右 <right> 相同的行。例如：
nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2
INTERSECT
GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2;
返回
=======================
| id | col_1 | col_2 |
=======================
| 104 | 1 | 2 | -- line 1
-----------------------
MINUSGraph
返回 A - B 数据的差集，此处请注意运算顺序。例如：
nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2
MINUS
GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2;
返回
========================
| id | col_1 | col_2 |
========================
| 215 | 4 | 3 | -- line 3
------------------------
如果更改 MINUS 顺序
nebula> GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2
MINUS
GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS col_1, $$.tag.prop2 AS col_2;
则返回
=======================
| id | col_1 | col_2 | -- column named from query 2
=======================
| 104 | 2 | 2 | -- line 2
-----------------------
集合操作和管道的优先级Graph
请注意当一条查询同时包含管道 | 和集合操作时，管道的优先级高于集合操作。管道用法请参考Graph。语句 GO FROM 1 UNION GO FROM 2 | GO FROM 3 等价于语句 GO FROM 1 UNION (GO FROM 2 | GO FROM 3)。
例如：
nebula> GO FROM 100 OVER follow YIELD follow._dst AS play_dst \
UNION \
GO FROM 200 OVER serve REVERSELY YIELD serve._dst AS play_dst \
| GO FROM $-.play_dst OVER follow YIELD follow._dst AS play_dst;
红色框内的语句先执行，然后再执行绿色框内的语句。
nebula> (GO FROM 100 OVER follow YIELD follow._dst AS play_dst \
UNION \
GO FROM 200 OVER serve REVERSELY YIELD serve._dst AS play_dst) \
| GO FROM $-.play_dst OVER follow YIELD follow._dst AS play_dst;
以上语句中，括号改变了执行的优先级，括号内的语句先执行。