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

  1. <left> UNION [DISTINCT | ALL] <right>

<left> 和 <right> 必须列数相同，且数据类型相同。

示例

  1. nebula> GO FROM 1 OVER e1 \
  2.         UNION \
  3.         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。

  1. nebula> GO FROM 1 OVER e1 \
  2.         UNION ALL\
  3.         GO FROM 2 OVER e1

以上语句返回点 1 和 2 关联的点，其中存在重复点。

UNION 亦可与 YIELD 同时使用，例如以下语句：

  1. nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS left_1, $$.tag.prop2 AS left_2 -- query 1
  2. ==========================
  3. | id  | left_1 | left_2  |
  4. ==========================
  5. | 104 |    1   |    2    |    -- line 1
  6. --------------------------
  7. | 215 |    4   |    3    |    -- line 3
  8. --------------------------
  10. nebula> GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2  -- query 2
  11. ===========================
  12. | id  | right_1 | right_2 |
  13. ===========================
  14. | 104 |    1    |    2    |    -- line 1
  15. ---------------------------
  16. | 104 |    2    |    2    |    -- line 2
  17. ---------------------------
  1. nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS left_1, $$.tag.prop2 AS left_2
  2. UNION /* DISTINCT */
  3. GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2

以上语句返回

  1. =========================
  2. | id  | left_1 | left_2 |    -- UNION or UNION DISTINCT. The column names come from query 1
  3. =========================
  4. | 104 |    1   |    2   |    -- line 1
  5. -------------------------
  6. | 104 |    2   |    2   |    -- line 2
  7. -------------------------
  8. | 215 |    4   |    3   |    -- line 3
  9. -------------------------

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

  1. nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS left_1, $$.tag.prop2 AS left_2   \
  2.         UNION ALL   \
  3.         GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2
  5. =========================
  6. | id  | left_1 | left_2 |    -- UNION ALL
  7. =========================
  8. | 104 |    1   |    2   |    -- line 1
  9. -------------------------
  10. | 104 |    1   |    2   |    -- line 1
  11. -------------------------
  12. | 104 |    2   |    2   |    -- line 2
  13. -------------------------
  14. | 215 |    4   |    3   |    -- line 3
  15. -------------------------

INTERSECT

INTERSECT 返回集合 A 和 B ( A ⋂ B)的交集。

  1. <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：

  1. nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS left_1, $$.tag.prop2 AS left_2
  2. INTERSECT
  3. GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2

返回

  1. =========================
  2. | id  | left_1 | left_2 |
  3. =========================
  4. | 104 |    1   |    2   |    -- line 1
  5. -------------------------

MINUS

返回 A - B 数据的差集，此处请注意运算顺序。例如：

  1. nebula> GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS left_1, $$.tag.prop2 AS left_2
  2. MINUS
  3. GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2

返回

  1. ==========================
  2. | id  | left_1 | left_2  |
  3. ==========================
  4. | 215 |    4   |    3    |     -- line 3
  5. --------------------------

如果更改 MINUS 顺序

  1. nebula> GO FROM 2,3 OVER e1 YIELD e1._dst AS id, e1.prop1 AS right_1, $$.tag.prop2 AS right_2
  2. MINUS
  3. GO FROM 1 OVER e1 YIELD e1._dst AS id, e1.prop1 AS left_1, $$.tag.prop2 AS left_2

则返回

  1. ===========================
  2. | id  | right_1 | right_2 |    -- column named from query 2
  3. ===========================
  4. | 104 |    2    |    2    |    -- line 2
  5. ---------------------------