//与match区别：如果没有匹配到，返回NULL

CREATE (olive:Person {name:'Olive Stone'}),

(charlie:Person {name:'Charlie Sheen'}),

(michael:Person {name:'Michael Douglas'}),

(martin:Person {name:'Martin Sheen'}),

(rob:Person {name:'Rob Reiner'}),

(wallstreet:Movie {name:'WallStreet',title:"Wall Street"}),

(president:Movie {name:'TheAmericanPresident',title:"The American President"}),

(olive)-[:DIRECTED]->(wallstreet),

(charlie)-[:ACTED_IN]->(wallstreet),

(michael)-[:ACTED_IN]->(wallstreet),

(martin)-[:ACTED_IN]->(wallstreet),

(michael)-[:ACTED_IN]->(president),

(rob)-[:DIRECTED]->(president),

(martin)-[:ACTED_IN]->(president),

(charlie)-[:FATHER]->(martin)

1.可选元素

//返回null，节点没有外向的关系

match(a:Movie{title:"Wall Street"}) optional match(a)-->(x) return x

2.可选元素的属性

// 如果可选的元素返回null，那么该元素的属性也返回null

match(a:Movie{title:"Wall Street"}) optional match(a)-->(x) return x,x.name

3.可选关系类型

//返回null

match(a:Movie{title:"Wall Street"}) optional match(a)-[r:ACTED_IN]->() return r