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集合操作 (UNION，INTERSECT， MINUS)

UNION，UNION DISTINCT，UNION ALL

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，将按照类型转换进行转换。

示例

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 left_1, $$.tag.prop2 AS left_2 -- query 1
==========================
| id  | left_1 | left_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 right_1, $$.tag.prop2 AS right_2  -- query 2
===========================
| id  | right_1 | right_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 left_1, $$.tag.prop2 AS left_2   \
        UNION /* DISTINCT */     \
        GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2

以上语句返回

=========================
| id  | left_1 | left_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 left_1, $$.tag.prop2 AS left_2   \
        UNION ALL   \
        GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2

=========================
| id  | left_1 | left_2 |    -- UNION ALL
=========================
| 104 |    1   |    2   |    -- line 1
-------------------------
| 104 |    1   |    2   |    -- line 1
-------------------------
| 104 |    2   |    2   |    -- line 2
-------------------------
| 215 |    4   |    3   |    -- line 3
-------------------------

INTERSECT

INTERSECT 返回集合 A 和 B ( A ⋂ B)的交集。

<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 left_1, $$.tag.prop2 AS left_2
INTERSECT
GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2

返回

=========================
| id  | left_1 | left_2 |
=========================
| 104 |    1   |    2   |    -- line 1
-------------------------

MINUS

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 left_1, $$.tag.prop2 AS left_2
MINUS
GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2

返回

==========================
| id  | left_1 | left_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 right_1, $$.tag.prop2 AS right_2
MINUS
GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS left_1, $$.tag.prop2 AS left_2

则返回

===========================
| id  | right_1 | right_2 |    -- column named from query 2
===========================
| 104 |    2    |    2    |    -- line 2
---------------------------