YIELDGraph

YIELD定义 nGQL 查询的输出结果。

YIELD可以引导子句或语句：

• YIELD子句可以用于原生 nGQL 语句中，例如GO、FETCH或LOOKUP。

• YIELD语句可以在独立查询或复合查询中使用。

openCypher 兼容性Graph

本文操作仅适用于原生 nGQL。关于 openCypher 方式如何定义输出结果，请参见 Graph。

YIELD在 nGQL 和 openCypher 中有不同的函数：

• 在 openCypher 中，YIELD用于在CALL[…YIELD]子句中指定过程调用的输出。

  Note

  nGQL 不支持CALL[…YIELD]。

• 在 nGQL 中，YIELD和 openCypher 中的RETURN类似。

YIELD 子句Graph

语法Graph

YIELD [DISTINCT] <col> [AS <alias>] [, <col> [AS <alias>] ...];

使用 YIELD 子句Graph

• GO语句中使用YIELD：

  nebula> GO FROM "player100" OVER follow \
          YIELD properties($$).name AS Friend, properties($$).age AS Age;
  +-----------------+-----+
  | Friend          | Age |
  +-----------------+-----+
  | "Tony Parker"   | 36  |
  | "Manu Ginobili" | 41  |
  +-----------------+-----+
  

• FETCH语句中使用YIELD：

  nebula> FETCH PROP ON player "player100" \
          YIELD properties(vertex).name;
  +-------------+-------------------------+
  | VertexID    | properties(VERTEX).name |
  +-------------+-------------------------+
  | "player100" | "Tim Duncan"            |
  +-------------+-------------------------+
  

• LOOKUP语句中使用YIELD：

  nebula> LOOKUP ON player WHERE player.name == "Tony Parker" \
          YIELD properties(vertex).name, properties(vertex).age;
  +-------------+-------------------------+------------------------+
  | VertexID    | properties(VERTEX).name | properties(VERTEX).age |
  +-------------+-------------------------+------------------------+
  | "player101" | "Tony Parker"           | 36                     |
  +-------------+-------------------------+------------------------+
  

YIELD 语句Graph

语法Graph

YIELD [DISTINCT] <col> [AS <alias>] [, <col> [AS <alias>] ...]
[WHERE <conditions>];

复合查询中使用 YIELD 语句Graph

在Graph中，YIELD语句可以接收、过滤、修改之前语句的结果集，然后输出。

# 查找 player100 关注的 player，并计算他们的平均年龄。
nebula> GO FROM "player100" OVER follow \
        YIELD dst(edge) AS ID \
        | FETCH PROP ON player $-.ID \
        YIELD properties(vertex).age AS Age \
        | YIELD AVG($-.Age) as Avg_age, count(*)as Num_friends;
+---------+-------------+
| Avg_age | Num_friends |
+---------+-------------+
| 38.5    | 2           |
+---------+-------------+

# 查找 player101 关注的 player，返回 degree 大于 90 的 player。
nebula> $var1 = GO FROM "player101" OVER follow \
        YIELD properties(edge).degree AS Degree, dst(edge) as ID; \
        YIELD $var1.ID AS ID WHERE $var1.Degree > 90;
+-------------+
| ID          |
+-------------+
| "player100" |
| "player125" |
+-------------+

独立使用 YIELD 语句Graph

YIELD可以计算表达式并返回结果。

nebula> YIELD rand32(1, 6);
+-------------+
| rand32(1,6) |
+-------------+
| 3           |
+-------------+

nebula> YIELD "Hel" + "\tlo" AS string1, ", World!" AS string2;
+-------------+------------+
| string1     | string2    |
+-------------+------------+
| "Hel    lo" | ", World!" |
+-------------+------------+

nebula> YIELD hash("Tim") % 100;
+-------------------+
| (hash("Tim")%100) |
+-------------------+
| 42                |
+-------------------+

nebula> YIELD \
      CASE 2+3 \
      WHEN 4 THEN 0 \
      WHEN 5 THEN 1 \
      ELSE -1 \
      END \
      AS result;
+--------+
| result |
+--------+
| 1      |
+--------+