WHERE

WHERE子句通常用于如下查询：

原生nGQL，例如GO和LOOKUP语句。
openCypher方式，例如MATCH和WITH语句。

不支持在WHERE子句中使用Pattern（TODO: planning），例如WHERE (v)-->(v2)。
过滤Rank是原生nGQL功能。如需在openCypher兼容语句中直接获取Rank值，可以使用rank()函数，例如MATCH (:player)-[e:follow]->() RETURN rank(e);。

nebula> GO FROM "player100" \
        OVER follow \
        WHERE follow.degree > 90 \
        OR $$.player.age != 33 \
        AND $$.player.name != "Tony Parker";
+-------------+
| follow._dst |
+-------------+
| "player101" |
+-------------+
| "player125" |
+-------------+

过滤属性

在WHERE子句中使用点或边的属性定义条件。

过滤点属性：

nebula> MATCH (v:player)-[e]->(v2) \
        WHERE v2.age < 25 \
        RETURN v2.name, v2.age;
+----------------------+--------+
| v2.name              | v2.age |
+----------------------+--------+
| "Luka Doncic"        | 20     |
+----------------------+--------+
| "Kristaps Porzingis" | 23     |
+----------------------+--------+
| "Ben Simmons"        | 22     |
+----------------------+--------+

nebula> GO FROM "player100" \
        OVER follow \
        WHERE $^.player.age >= 42;
+-------------+
| follow._dst |
+-------------+
| "player101" |
+-------------+
| "player125" |
+-------------+

过滤边属性：

nebula> MATCH (v:player)-[e]->() \
        WHERE e.start_year < 2000 \
        RETURN DISTINCT v.name, v.age;
+--------------------+-------+
| v.name             | v.age |
+--------------------+-------+
| "Shaquille O'Neal" | 47    |
+--------------------+-------+
| "Steve Nash"       | 45    |
+--------------------+-------+
| "Ray Allen"        | 43    |
+--------------------+-------+
| "Grant Hill"       | 46    |
+--------------------+-------+
| "Tony Parker"      | 36    |
...

过滤动态计算属性

nebula> MATCH (v:player) \
        WHERE v[toLower("AGE")] < 21 \
        RETURN v.name, v.age;
+---------------+-------+
| v.name        | v.age |
+---------------+-------+
+---------------+-------+

nebula> MATCH (v:player) \
        WHERE exists(v.age) \
        RETURN v.name, v.age;
+-------------------------+-------+
| v.name                  | v.age |
+-------------------------+-------+
| "Boris Diaw"            | 36    |
+-------------------------+-------+
| "DeAndre Jordan"        | 30    |
+-------------------------+-------+

过滤rank

在nGQL中，如果多个边拥有相同的起始点、目的点和属性，则它们的唯一区别是rank值。在WHERE子句中可以使用rank过滤边。

# 创建测试数据。
nebula> CREATE SPACE test (vid_type=FIXED_STRING(30));
nebula> USE test;
nebula> CREATE EDGE e1(p1 int);
nebula> CREATE TAG person(p1 int);
nebula> INSERT VERTEX person(p1) VALUES "1":(1);
nebula> INSERT VERTEX person(p1) VALUES "2":(2);
nebula> INSERT EDGE e1(p1) VALUES "1"->"2"@0:(10);
nebula> INSERT EDGE e1(p1) VALUES "1"->"2"@1:(11);
nebula> INSERT EDGE e1(p1) VALUES "1"->"2"@2:(12);
nebula> INSERT EDGE e1(p1) VALUES "1"->"2"@3:(13);
nebula> INSERT EDGE e1(p1) VALUES "1"->"2"@4:(14);
nebula> INSERT EDGE e1(p1) VALUES "1"->"2"@5:(15);
nebula> INSERT EDGE e1(p1) VALUES "1"->"2"@6:(16);
# 通过rank过滤边，查找rank大于2的边。
nebula> GO FROM "1" \
        OVER e1 \
        WHERE e1._rank>2 \
        YIELD e1._src, e1._dst, e1._rank AS Rank, e1.p1 | \
        ORDER BY $-.Rank DESC;
====================================
| e1._src | e1._dst | Rank | e1.p1 |
====================================
| 1       | 2       | 6    | 16    |
------------------------------------
| 1       | 2       | 5    | 15    |
------------------------------------
| 1       | 2       | 4    | 14    |
------------------------------------
| 1       | 2       | 3    | 13    |
------------------------------------

在WHERE子句中使用STARTS WITH、ENDS WITH或CONTAINS可以匹配字符串的特定部分。匹配时区分大小写。

`STARTS WITH`

# 查询姓名以T开头的player信息。
nebula> MATCH (v:player) \
        WHERE v.name STARTS WITH "T" \
        RETURN v.name, v.age;
+------------------+-------+
| v.name           | v.age |
+------------------+-------+
| "Tracy McGrady"  | 39    |
+------------------+-------+
| "Tony Parker"    | 36    |
+------------------+-------+
| "Tim Duncan"     | 42    |
+------------------+-------+
| "Tiago Splitter" | 34    |
+------------------+-------+

如果使用小写t（STARTS WITH "t"），会返回空集，因为数据库中没有以小写t开头的姓名。

ENDS WITH会从字符串的结束位置开始匹配。

nebula> MATCH (v:player) \
        WHERE v.name ENDS WITH "r" \
        RETURN v.name, v.age;
+------------------+-------+
+------------------+-------+
| "Vince Carter"   | 42    |
+------------------+-------+
| "Tony Parker"    | 36    |
+------------------+-------+
| "Tiago Splitter" | 34    |
+------------------+-------+

`CONTAINS`

CONTAINS会检查关键字是否匹配字符串的某一部分。

nebula> MATCH (v:player) \
        WHERE v.name CONTAINS "Pa" \
        RETURN v.name, v.age;
+---------------+-------+
| v.name        | v.age |
+---------------+-------+
| "Paul George" | 28    |
+---------------+-------+
| "Tony Parker" | 36    |
+---------------+-------+
| "Paul Gasol"  | 38    |
+---------------+-------+
| "Chris Paul"  | 33    |
+---------------+-------+

结合NOT使用

用户可以结合布尔运算符NOT一起使用，否定字符串匹配条件。

nebula> MATCH (v:player) \
        WHERE NOT v.name ENDS WITH "R" \
        RETURN v.name, v.age;
+-------------------------+-------+
| v.name                  | v.age |
+-------------------------+-------+
| "Rajon Rondo"           | 33    |
+-------------------------+-------+
| "Rudy Gay"              | 32    |
+-------------------------+-------+
| "Dejounte Murray"       | 29    |
+-------------------------+-------+
| "Chris Paul"            | 33    |
+-------------------------+-------+
| "Carmelo Anthony"       | 34    |
+-------------------------+-------+
...

使用IN运算符检查某个值是否在指定列表中。

nebula> MATCH (v:player) \
        WHERE v.age IN range(20,25) \
        RETURN v.name, v.age;
+-------------------------+-------+
| v.name                  | v.age |
+-------------------------+-------+
| "Ben Simmons"           | 22    |
+-------------------------+-------+
| "Kristaps Porzingis"    | 23    |
+-------------------------+-------+
| "Luka Doncic"           | 20    |
+-------------------------+-------+
| "Kyle Anderson"         | 25    |
+-------------------------+-------+
| "Giannis Antetokounmpo" | 24    |
+-------------------------+-------+
| "Joel Embiid"           | 25    |
+-------------------------+-------+
nebula> LOOKUP ON player WHERE player.age IN [25,28]  YIELD player.name, player.age;
+-------------+------------------+------------+
| VertexID    | player.name      | player.age |
+-------------+------------------+------------+
| "player135" | "Damian Lillard" | 28         |
+-------------+------------------+------------+
| "player131" | "Paul George"    | 28         |
+-------------+------------------+------------+
| "player130" | "Joel Embiid"    | 25         |
+-------------+------------------+------------+
| "player123" | "Ricky Rubio"    | 28         |
+-------------+------------------+------------+
| "player106" | "Kyle Anderson"  | 25         |