RETURN¶
RETURN
子句定义了 nGQL 查询的输出结果。如果需要返回多个字段,用英文逗号(,)分隔。
RETURN
可以引导子句或语句:
RETURN
子句可以用于 nGQL 中的 openCypher 方式语句中,例如MATCH
或UNWIND
。
RETURN
可以单独使用,输出表达式的结果。
openCypher 兼容性¶
本文操作仅适用于 nGQL 中的 openCypher 方式。关于原生 nGQL 如何定义输出结果,请参见 YIELD
。
RETURN
不支持如下 openCypher 功能:
-
使用不在英文字母表中的字符作为变量名。例如:
MATCH (`点 1`:player) \ RETURN `点 1`;
-
设置一个模式,并返回该模式匹配的所有元素。例如:
MATCH (v:player) \ RETURN (v)-[e]->(v2);
历史版本兼容性¶
- 在 nGQL 1.x 中,
RETURN
适用于原生 nGQL,语法为RETURN <var_ref> IF <var_ref> IS NOT NULL
。
- 从 nGQL 2.0 开始,
RETURN
不适用于原生 nGQL。
Map 顺序说明¶
RETURN
返回 Map 时,Key 的顺序是未定义的。
nebula> RETURN {age: 32, name: "Marco Belinelli"};
+------------------------------------+
| {age:32,name:"Marco Belinelli"} |
+------------------------------------+
| {age: 32, name: "Marco Belinelli"} |
+------------------------------------+
nebula> RETURN {zage: 32, name: "Marco Belinelli"};
+-------------------------------------+
| {zage:32,name:"Marco Belinelli"} |
+-------------------------------------+
| {name: "Marco Belinelli", zage: 32} |
+-------------------------------------+
返回点或边¶
使用RETURN {<vertex_name> | <edge_name>}
返回点或边的所有信息。
// 返回点
nebula> MATCH (v:player) \
RETURN v;
+---------------------------------------------------------------+
| v |
+---------------------------------------------------------------+
| ("player104" :player{age: 32, name: "Marco Belinelli"}) |
| ("player107" :player{age: 32, name: "Aron Baynes"}) |
| ("player116" :player{age: 34, name: "LeBron James"}) |
| ("player120" :player{age: 29, name: "James Harden"}) |
| ("player125" :player{age: 41, name: "Manu Ginobili"}) |
+---------------------------------------------------------------+
...
// 返回边
nebula> MATCH (v:player)-[e]->() \
RETURN e;
+------------------------------------------------------------------------------+
| e |
+------------------------------------------------------------------------------+
| [:follow "player104"->"player100" @0 {degree: 55}] |
| [:follow "player104"->"player101" @0 {degree: 50}] |
| [:follow "player104"->"player105" @0 {degree: 60}] |
| [:serve "player104"->"team200" @0 {end_year: 2009, start_year: 2007}] |
| [:serve "player104"->"team208" @0 {end_year: 2016, start_year: 2015}] |
+------------------------------------------------------------------------------+
...
返回点 ID¶
使用id()
函数返回点 ID。
nebula> MATCH (v:player{name:"Tim Duncan"}) \
RETURN id(v);
+-------------+
| id(v) |
+-------------+
| "player100" |
+-------------+
返回 Tag¶
使用labels()
函数返回点上的 Tag 列表。
nebula> MATCH (v:player{name:"Tim Duncan"}) \
RETURN labels(v);
+------------+
| labels(v) |
+------------+
| ["player"] |
+------------+
返回列表labels(v)
中的第 N 个元素,可以使用labels(v)[n-1]
。例如下面示例使用labels(v)[0]
检索第一个元素。
nebula> MATCH (v:player{name:"Tim Duncan"}) \
RETURN labels(v)[0];
+--------------+
| labels(v)[0] |
+--------------+
| "player" |
+--------------+
返回属性¶
使用语法<vertex_name>.<tag_name>.<property_name>
返回点的属性;使用语法<edge_name>.<property_name>
返回边的属性。
// 返回点的属性
nebula> MATCH (v:player) \
RETURN v.player.name, v.player.age \
LIMIT 3;
+------------------+--------------+
| v.player.name | v.player.age |
+------------------+--------------+
| "Danny Green" | 31 |
| "Tiago Splitter" | 34 |
| "David West" | 38 |
+------------------+--------------+
// 返回边的属性
nebula> MATCH (v:player{name:"Tim Duncan"})-[e]->() \
RETURN e.start_year, e.degree \
+--------------+----------+
| e.start_year | e.degree |
+--------------+----------+
| __NULL__ | 95 |
| __NULL__ | 95 |
| 1997 | __NULL__ |
+--------------+----------+
使用properties()
函数返回点或边的所有属性。
nebula> MATCH p=(v:player{name:"Tim Duncan"})-[]->(v2) \
RETURN properties(v2);
+----------------------------------+
| properties(v2) |
+----------------------------------+
| {name: "Spurs"} |
| {age: 36, name: "Tony Parker"} |
| {age: 41, name: "Manu Ginobili"} |
+----------------------------------+
返回 Edge type¶
使用type()
函数返回匹配的 Edge type。
nebula> MATCH p=(v:player{name:"Tim Duncan"})-[e]->() \
RETURN DISTINCT type(e);
+----------+
| type(e) |
+----------+
| "serve" |
| "follow" |
+----------+
返回路径¶
使用RETURN <path_name>
返回匹配路径的所有信息。
nebula> MATCH p=(v:player{name:"Tim Duncan"})-[*3]->() \
RETURN p;
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| p |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})-[:follow@0 {degree: 90}]->("player102" :player{age: 33, name: "LaMarcus Aldridge"})-[:serve@0 {end_year: 2019, start_year: 2015}]->("team204" :team{name: "Spurs"})> |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})-[:follow@0 {degree: 90}]->("player102" :player{age: 33, name: "LaMarcus Aldridge"})-[:serve@0 {end_year: 2015, start_year: 2006}]->("team203" :team{name: "Trail Blazers"})> |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})-[:follow@0 {degree: 90}]->("player102" :player{age: 33, name: "LaMarcus Aldridge"})-[:follow@0 {degree: 75}]->("player101" :player{age: 36, name: "Tony Parker"})> |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
...
返回路径中的点¶
使用nodes()
函数返回路径中的所有点。
nebula> MATCH p=(v:player{name:"Tim Duncan"})-[]->(v2) \
RETURN nodes(p);
+-------------------------------------------------------------------------------------------------------------+
| nodes(p) |
+-------------------------------------------------------------------------------------------------------------+
| [("player100" :player{age: 42, name: "Tim Duncan"}), ("team204" :team{name: "Spurs"})] |
| [("player100" :player{age: 42, name: "Tim Duncan"}), ("player101" :player{age: 36, name: "Tony Parker"})] |
| [("player100" :player{age: 42, name: "Tim Duncan"}), ("player125" :player{age: 41, name: "Manu Ginobili"})] |
+-------------------------------------------------------------------------------------------------------------+
返回路径中的边¶
使用relationships()
函数返回路径中的所有边。
nebula> MATCH p=(v:player{name:"Tim Duncan"})-[]->(v2) \
RETURN relationships(p);
+-------------------------------------------------------------------------+
| relationships(p) |
+-------------------------------------------------------------------------+
| [[:serve "player100"->"team204" @0 {end_year: 2016, start_year: 1997}]] |
| [[:follow "player100"->"player101" @0 {degree: 95}]] |
| [[:follow "player100"->"player125" @0 {degree: 95}]] |
+-------------------------------------------------------------------------+
返回路径长度¶
使用length()
函数检索路径的长度。
nebula> MATCH p=(v:player{name:"Tim Duncan"})-[*..2]->(v2) \
RETURN p AS Paths, length(p) AS Length;
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+
| Paths | Length |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:serve@0 {end_year: 2016, start_year: 1997}]->("team204" :team{name: "Spurs"})> | 1 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})> | 1 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player125" :player{age: 41, name: "Manu Ginobili"})> | 1 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})-[:serve@0 {end_year: 2018, start_year: 1999}]->("team204" :team{name: "Spurs"})> | 2 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})-[:serve@0 {end_year: 2019, start_year: 2018}]->("team215" :team{name: "Hornets"})> | 2 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})-[:follow@0 {degree: 95}]->("player100" :player{age: 42, name: "Tim Duncan"})> | 2 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})-[:follow@0 {degree: 90}]->("player102" :player{age: 33, name: "LaMarcus Aldridge"})> | 2 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player101" :player{age: 36, name: "Tony Parker"})-[:follow@0 {degree: 95}]->("player125" :player{age: 41, name: "Manu Ginobili"})> | 2 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player125" :player{age: 41, name: "Manu Ginobili"})-[:serve@0 {end_year: 2018, start_year: 2002}]->("team204" :team{name: "Spurs"})> | 2 |
| <("player100" :player{age: 42, name: "Tim Duncan"})-[:follow@0 {degree: 95}]->("player125" :player{age: 41, name: "Manu Ginobili"})-[:follow@0 {degree: 90}]->("player100" :player{age: 42, name: "Tim Duncan"})> | 2 |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+
返回所有元素¶
使用星号(*)返回匹配模式中的所有元素。
nebula> MATCH (v:player{name:"Tim Duncan"}) \
RETURN *;
+----------------------------------------------------+
| v |
+----------------------------------------------------+
| ("player100" :player{age: 42, name: "Tim Duncan"}) |
+----------------------------------------------------+
nebula> MATCH (v:player{name:"Tim Duncan"})-[e]->(v2) \
RETURN *;
+----------------------------------------------------+-----------------------------------------------------------------------+-------------------------------------------------------+
| v | e | v2 |
+----------------------------------------------------+-----------------------------------------------------------------------+-------------------------------------------------------+
| ("player100" :player{age: 42, name: "Tim Duncan"}) | [:follow "player100"->"player101" @0 {degree: 95}] | ("player101" :player{age: 36, name: "Tony Parker"}) |
| ("player100" :player{age: 42, name: "Tim Duncan"}) | [:follow "player100"->"player125" @0 {degree: 95}] | ("player125" :player{age: 41, name: "Manu Ginobili"}) |
| ("player100" :player{age: 42, name: "Tim Duncan"}) | [:serve "player100"->"team204" @0 {end_year: 2016, start_year: 1997}] | ("team204" :team{name: "Spurs"}) |
+----------------------------------------------------+-----------------------------------------------------------------------+-------------------------------------------------------+
重命名字段¶
使用语法AS <alias>
重命名输出结果中的字段。
nebula> MATCH (v:player{name:"Tim Duncan"})-[:serve]->(v2) \
RETURN v2.team.name AS Team;
+---------+
| Team |
+---------+
| "Spurs" |
+---------+
nebula> RETURN "Amber" AS Name;
+---------+
| Name |
+---------+
| "Amber" |
+---------+
返回不存在的属性¶
如果匹配的结果中,某个属性不存在,会返回NULL
。
nebula> MATCH (v:player{name:"Tim Duncan"})-[e]->(v2) \
RETURN v2.player.name, type(e), v2.player.age;
+-----------------+----------+---------------+
| v2.player.name | type(e) | v2.player.age |
+-----------------+----------+---------------+
| "Manu Ginobili" | "follow" | 41 |
| __NULL__ | "serve" | __NULL__ |
| "Tony Parker" | "follow" | 36 |
+-----------------+----------+---------------+
返回表达式结果¶
RETURN
语句可以返回字面量、函数或谓词等表达式的结果。
nebula> MATCH (v:player{name:"Tony Parker"})-->(v2:player) \
RETURN DISTINCT v2.player.name, "Hello"+" graphs!", v2.player.age > 35;
+---------------------+----------------------+--------------------+
| v2.player.name | ("Hello"+" graphs!") | (v2.player.age>35) |
+---------------------+----------------------+--------------------+
| "LaMarcus Aldridge" | "Hello graphs!" | false |
| "Tim Duncan" | "Hello graphs!" | true |
| "Manu Ginobili" | "Hello graphs!" | true |
+---------------------+----------------------+--------------------+
nebula> RETURN 1+1;
+-------+
| (1+1) |
+-------+
| 2 |
+-------+
nebula> RETURN 3 > 1;
+-------+
| (3>1) |
+-------+
| true |
+-------+
nebula> RETURN 1+1, rand32(1, 5);
+-------+-------------+
| (1+1) | rand32(1,5) |
+-------+-------------+
| 2 | 1 |
+-------+-------------+
返回唯一字段¶
使用DISTINCT
可以删除结果集中的重复字段。
# 未使用 DISTINCT。
nebula> MATCH (v:player{name:"Tony Parker"})--(v2:player) \
RETURN v2.player.name, v2.player.age;
+---------------------+--------+
| v2.name | v2.age |
+---------------------+--------+
| "Tim Duncan" | 42 |
| "LaMarcus Aldridge" | 33 |
| "Marco Belinelli" | 32 |
| "Boris Diaw" | 36 |
| "Dejounte Murray" | 29 |
| "Tim Duncan" | 42 |
| "LaMarcus Aldridge" | 33 |
| "Manu Ginobili" | 41 |
+---------------------+--------+
# 使用 DISTINCT。
nebula> MATCH (v:player{name:"Tony Parker"})--(v2:player) \
RETURN DISTINCT v2.player.name, v2.player.age;
+---------------------+--------+
| v2.name | v2.age |
+---------------------+--------+
| "Tim Duncan" | 42 |
| "LaMarcus Aldridge" | 33 |
| "Marco Belinelli" | 32 |
| "Boris Diaw" | 36 |
| "Dejounte Murray" | 29 |
| "Manu Ginobili" | 41 |
+---------------------+--------+