集合运算符

    所有集合运算符的优先级相同，如果一个nGQL语句中有多个集合运算符，Nebula Graph会从左到右进行计算，除非用括号指定顺序。

    集合运算符仅适用于原生nGQL。

    • 运算符UNION DISTINCT（或使用缩写UNION）返回两个集合A和B的并集，不包含重复的元素。

    • 运算符UNION ALL返回两个集合A和B的并集，包含重复的元素。

    1. # 返回两个查询结果的并集，不包含重复的元素。
    2. nebula> GO FROM "player102" OVER follow \
    3.         UNION \
    4.         GO FROM "player100" OVER follow;
    5. +-------------+
    6. | follow._dst |
    7. +-------------+
    8. | "player101" |
    9. +-------------+
    10. | "player102" |
    11. +-------------+
    13. # 返回两个查询结果的并集，包含重复的元素。
    14. nebula> GO FROM "player102" OVER follow \
    15.         GO FROM "player100" OVER follow;
    16. +-------------+
    17. | follow._dst |
    18. +-------------+
    19. | "player101" |
    21. | "player101" |
    22. +-------------+
    23. | "player102" |
    24. +-------------+
    26. # UNION也可以和YIELD语句一起使用，去重时会检查每一行的所有列，每列都相同时才会去重。
    27. nebula> GO FROM "player102" OVER follow \
    28.         YIELD follow._dst AS id, follow.degree AS Degree, $$.player.age AS Age \
    29.         UNION /* DISTINCT */ \
    30.         GO FROM "player100" OVER follow \
    31.         YIELD follow._dst AS id, follow.degree AS Degree, $$.player.age AS Age;
    32. +-------------+--------+-----+
    33. | id          | Degree | Age |
    34. +-------------+--------+-----+
    35. | "player101" | 75     | 36  |     
    36. +-------------+--------+-----+
    37. | "player101" | 96     | 36  |       
    38. +-------------+--------+-----+
    39. | "player102" | 90     | 33  |     
    40. +-------------+--------+-----+

    • left和right必须有相同数量的列和数据类型。如果需要转换数据类型，请参见类型转换。

    1. nebula> GO FROM "player102" OVER follow \
    2.         YIELD follow._dst AS id, follow.degree AS Degree, $$.player.age AS Age \
    3.         INTERSECT \
    4.         GO FROM "player100" OVER follow \
    5.         YIELD follow._dst AS id, follow.degree AS Degree, $$.player.age AS Age;

    运算符MINUS返回两个集合A和B的差异，即A-B。请注意left和right的顺序，A-B表示在集合A中，但是不在集合B中的元素。

    1. nebula> GO FROM "player100" OVER follow \
    2.         MINUS \
    3.         GO FROM "player102" OVER follow;
    4. +-------------+
    5. | follow._dst |
    6. +-------------+
    7. | "player102" |
    8. +-------------+
    10. nebula> GO FROM "player102" OVER follow \
    11.         MINUS \
    12.         GO FROM "player100" OVER follow;
    13. Empty set (time spent 2243/3259 us)

    当查询包含集合运算符和管道符（|）时，的优先级高。例如GO FROM 1 UNION GO FROM 2 | GO FROM 3相当于GO FROM 1 UNION (GO FROM 2 | GO FROM 3)。

    该查询会先执行红框内的语句，然后执行绿框的UNION操作。

    圆括号可以修改执行的优先级，例如：

    1. nebula> (GO FROM "player102" OVER follow \
    2.         YIELD follow._dst AS play_dst  \
    3.         UNION \
    4.         GO FROM "team200" OVER serve REVERSELY \
    5.         YIELD serve._dst AS play_dst) \
    6.         | GO FROM $-.play_dst OVER follow YIELD follow._dst AS play_dst;

    该查询中，圆括号包裹的部分先执行，即先执行UNION操作，再将结果结合管道符进行下一步操作。