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集合运算符Graph

合并多个请求时，可以使用集合运算符，包括UNION、UNION ALL、INTERSECT和MINUS。

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，NebulaGraph会从左到右进行计算，除非用括号指定顺序。

openCypher兼容性Graph

集合运算符仅适用于nGQL扩展。

UNION、UNION DISTINCT、UNION ALLGraph

<left> UNION [DISTINCT | ALL] <right> [ UNION [DISTINCT | ALL] <right> ...]
  • 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。
  • 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Graph。

示例Graph

# 返回两个查询结果的并集，不包含重复的元素。
nebula> GO FROM "player102" OVER follow \
    UNION \
    GO FROM "player100" OVER follow;
+-------------+
| follow._dst |
+-------------+
| "player101" |
+-------------+
| "player102" |
+-------------+

# 返回两个查询结果的并集，包含重复的元素。
nebula> GO FROM "player102" OVER follow \
    UNION ALL \
    GO FROM "player100" OVER follow;
+-------------+
| follow._dst |
+-------------+
| "player101" |
+-------------+
| "player101" |
+-------------+
| "player102" |
+-------------+

# 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。
nebula> GO FROM "player102" OVER follow \
        YIELD follow._dst AS id, follow.degree AS Degree, $$.player.age AS Age \
        UNION /* DISTINCT */ \
        GO FROM "player100" OVER follow \
        YIELD follow._dst AS id, follow.degree AS Degree, $$.player.age AS Age;
+-------------+--------+-----+
| id          | Degree | Age |
+-------------+--------+-----+
| "player101" | 75     | 36  |     
+-------------+--------+-----+
| "player101" | 96     | 36  |       
+-------------+--------+-----+
| "player102" | 90     | 33  |     
+-------------+--------+-----+

INTERSECTGraph

<left> INTERSECT <right>
  • 运算符INTERSECT返回两个集合A和B的交集。
  • 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Graph。

示例Graph

nebula> GO FROM "player102" OVER follow \
        YIELD follow._dst AS id, follow.degree AS Degree, $$.player.age AS Age \
        INTERSECT \
        GO FROM "player100" OVER follow \
        YIELD follow._dst AS id, follow.degree AS Degree, $$.player.age AS Age;
Empty set (time spent 2990/3511 us)

MINUSGraph

<left> MINUS <right>

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。

示例Graph

nebula> GO FROM "player100" OVER follow \
        MINUS \
        GO FROM "player102" OVER follow;
+-------------+
| follow._dst |
+-------------+
| "player102" |
+-------------+

nebula> GO FROM "player102" OVER follow \
        MINUS \
        GO FROM "player100" OVER follow;
Empty set (time spent 2243/3259 us)

集合运算符和管道符的优先级Graph

当查询包含集合运算符和管道符（|）时，Graph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)。

示例Graph

nebula> GO FROM "player102" OVER follow \
        YIELD follow._dst AS play_dst  \
        UNION \
        GO FROM "team200" OVER serve REVERSELY \
        YIELD serve._dst AS play_dst \
        | GO FROM $-.play_dst OVER follow YIELD follow._dst AS play_dst;

+-------------+
| play_dst    |
+-------------+
| "player101" |
+-------------+
| "player102" |
+-------------+

image

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：

nebula> (GO FROM "player102" OVER follow \
        YIELD follow._dst AS play_dst  \
        UNION \
        GO FROM "team200" OVER serve REVERSELY \
        YIELD serve._dst AS play_dst) \
        | 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。

最后更新: March 24, 2021
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