LOOKUP 语法Graph
LOOKUP 语句指定过滤条件对数据进行查询。LOOKUP 语句之后通常跟着 WHERE 子句。WHERE 子句用于向条件中添加过滤性的谓词，从而对数据进行过滤。
注意： 在使用 LOOKUP 语句之前，请确保已创建索引。查看Graph了解有关索引的更多信息。
LOOKUP ON {<vertex_tag> | <edge_type>} WHERE <expression> [ AND | UNION expression ...]) ] [YIELD <return_list>]
<return_list>
<col_name> [AS <col_alias>] [, <col_name> [AS <col_alias>] ...]
LOOKUP语句用于寻找点或边的集合。WHERE指定被筛选的逻辑条件。同样支持逻辑关键词 AND、UNION、NOT，详情参见 Graph 的用法。 注意：WHERE子句在LOOKUP中暂不支持如下操作：$-和$^- 在关系表达式中，暂不支持操作符两边都是field-name 的表达式，如 (tagName.column1 > tagName.column2)
- 暂不支持运算表达式和 function 表达式中嵌套 AliasProp 表达式。
YIELD指定返回结果。如未指定，则在LOOKUP标签时返回点 ID，在LOOKUP边类型时返回边的起点 ID、终点 ID 和 ranking 值。
点查询Graph
如下示例返回名称为 Tony Parker，标签为 player 的顶点。
nebula> CREATE TAG INDEX index_player ON player(name, age);
nebula> LOOKUP ON player WHERE player.name == "Tony Parker";
============
| VertexID |
============
| 101 |
------------
nebula> LOOKUP ON player WHERE player.name == "Tony Parker" \
YIELD player.name, player.age;
=======================================
| VertexID | player.name | player.age |
=======================================
| 101 | Tony Parker | 36 |
---------------------------------------
nebula> LOOKUP ON player WHERE player.name== "Kobe Bryant" YIELD player.name AS name | \
GO FROM $-.VertexID OVER serve YIELD $-.name, serve.start_year, serve.end_year, $$.team.name;
==================================================================
| $-.name | serve.start_year | serve.end_year | $$.team.name |
==================================================================
| Kobe Bryant | 1996 | 2016 | Lakers |
------------------------------------------------------------------
边查询Graph
如下示例返回 degree 为 90，边类型为 follow 的边。
nebula> CREATE EDGE INDEX index_follow ON follow(degree);
nebula> LOOKUP ON follow WHERE follow.degree == 90;
=============================
| SrcVID | DstVID | Ranking |
=============================
| 100 | 106 | 0 |
-----------------------------
nebula> LOOKUP ON follow WHERE follow.degree == 90 YIELD follow.degree;
=============================================
| SrcVID | DstVID | Ranking | follow.degree |
=============================================
| 100 | 106 | 0 | 90 |
---------------------------------------------
nebula> LOOKUP ON follow WHERE follow.degree == 90 YIELD DISTINCT follow._src;
===========================================
| SrcVID | DstVID | Ranking | follow._src |
===========================================
| 121 | 116 | 0 | 121 |
-------------------------------------------
| 140 | 114 | 0 | 140 |
-------------------------------------------
| 142 | 117 | 0 | 142 |
-------------------------------------------
| 133 | 114 | 0 | 133 |
-------------------------------------------
| 143 | 150 | 0 | 143 |
-------------------------------------------
| 114 | 103 | 0 | 114 |
-------------------------------------------
| 136 | 117 | 0 | 136 |
-------------------------------------------
| 127 | 114 | 0 | 127 |
-------------------------------------------
| 147 | 136 | 0 | 147 |
-------------------------------------------
| 118 | 120 | 0 | 118 |
-------------------------------------------
| 128 | 116 | 0 | 128 |
-------------------------------------------
| 138 | 115 | 0 | 138 |
-------------------------------------------
| 129 | 116 | 0 | 129 |
-------------------------------------------
nebula> LOOKUP ON follow WHERE follow.degree == 90 YIELD DISTINCT follow._dst;
===========================================
| SrcVID | DstVID | Ranking | follow._dst |
===========================================
| 121 | 116 | 0 | 116 |
-------------------------------------------
| 140 | 114 | 0 | 114 |
-------------------------------------------
| 142 | 117 | 0 | 117 |
-------------------------------------------
| 133 | 114 | 0 | 114 |
-------------------------------------------
| 114 | 103 | 0 | 103 |
-------------------------------------------
| 136 | 117 | 0 | 117 |
-------------------------------------------
| 118 | 120 | 0 | 120 |
-------------------------------------------
| 128 | 116 | 0 | 116 |
-------------------------------------------
nebula> LOOKUP ON follow WHERE follow.degree == 60 YIELD follow.degree AS Degree | \
GO FROM $-.DstVID OVER serve YIELD $-.DstVID, serve.start_year, serve.end_year, $$.team.name;
================================================================
| $-.DstVID | serve.start_year | serve.end_year | $$.team.name |
================================================================
| 105 | 2010 | 2018 | Spurs |
----------------------------------------------------------------
| 105 | 2009 | 2010 | Cavaliers |
----------------------------------------------------------------
| 105 | 2018 | 2019 | Raptors |
----------------------------------------------------------------
FAQGraph
错误码411Graph
[ERROR (-8)]: Unknown error(411):
错误码411表示WHERE过滤时没有有效的索引。NebulaGraph的索引使用的是最左匹配原则，即从最左边的为起点任何连续的索引都能匹配上。例如：
# 为标签t的前三个属性创建索引。
nebula> CREATE TAG INDEX example_index ON TAG t(p1, p2, p3);
# 无法匹配索引，因为不是从p1开始。
nebula> LOOKUP ON t WHERE p2 == 1 and p3 == 1;
# 可以匹配索引。
nebula> LOOKUP ON t WHERE p1 == 1;
# 可以匹配索引，因为p1和p2是连续的。
nebula> LOOKUP ON t WHERE p1 == 1 and p2 == 1;
# 可以匹配索引，因为p1、p2、p3是连续的。
nebula> LOOKUP ON t WHERE p1 == 1 and p2 == 1 and p3 == 1;
最后更新: 2021年5月14日