Neo4j 简明教程

Neo4j CQL - Introduction

CQL 是 Cypher 查询语言的简称。就像 Oracle Database 具有 SQL 查询语言一样，Neo4j 具有 CQL 作为查询语言。

CQL stands for Cypher Query Language. Like Oracle Database has query language SQL, Neo4j has CQL as query language.

Neo4j CQL

  1. Is a query language for Neo4j Graph Database.

  2. Is a declarative pattern-matching language.

  3. Follows SQL like syntax.

  4. Syntax is very simple and in human readable format.

Like Oracle SQL

  1. Neo4j CQL has commands to perform Database operations.

  2. Neo4j CQL supports many clauses such as WHERE, ORDER BY, etc., to write very complex queries in an easy manner.

  3. Neo4j CQL supports some functions such as String, Aggregation. In addition to them, it also supports some Relationship Functions.

Neo4j CQL Clauses

以下是 Neo4j *C*ypher *Q*uery *L*anguage 的读取子句：

Following are the read clauses of Neo4j *C*ypher *Q*uery *L*anguage −

Sr.No

Read Clauses

Usage

1

MATCH

This clause is used to search the data with a specified pattern.

2

OPTIONAL MATCH

This is the same as match, the only difference being it can use nulls in case of missing parts of the pattern.

3

WHERE

This clause id is used to add contents to the CQL queries.

4

START

This clause is used to find the starting points through the legacy indexes.

5

LOAD CSV

This clause is used to import data from CSV files.

以下是 Neo4j *C*ypher *Q*uery *L*anguage 的写入子句：

Following are the write clauses of Neo4j *C*ypher *Q*uery *L*anguage −

Sr.No

Write Clause

Usage

1

CREATE

This clause is used to create nodes, relationships, and properties.

2

MERGE

This clause verifies whether the specified pattern exists in the graph. If not, it creates the pattern.

3

SET

This clause is used to update labels on nodes, properties on nodes and relationships.

4

DELETE

This clause is used to delete nodes and relationships or paths etc. from the graph.

5

REMOVE

This clause is used to remove properties and elements from nodes and relationships.

6

FOREACH

This class is used to update the data within a list.

7

CREATE UNIQUE

Using the clauses CREATE and MATCH, you can get a unique pattern by matching the existing pattern and creating the missing one.

8

Importing CSV files with Cypher

Using Load CSV you can import data from .csv files.

以下是 Neo4j *C*ypher *Q*uery *L*anguage 的常用子句 -

Following are the general clauses of Neo4j *C*ypher *Q*uery *L*anguage −

Sr.No

General Clauses

Usage

1

RETURN

This clause is used to define what to include in the query result set.

2

ORDER BY

This clause is used to arrange the output of a query in order. It is used along with the clauses RETURN or WITH.

3

LIMIT

This clause is used to limit the rows in the result to a specific value.

4

SKIP

This clause is used to define from which row to start including the rows in the output.

5

WITH

This clause is used to chain the query parts together.

6

UNWIND

This clause is used to expand a list into a sequence of rows.

7

UNION

This clause is used to combine the result of multiple queries.

8

CALL

This clause is used to invoke a procedure deployed in the database.

Neo4j CQL Functions

以下是常用的 Neo4j CQL 函数 -

Following are the frequently used Neo4j CQL Functions −

Sr.No

CQL Functions

Usage

1

String

They are used to work with String literals.

2

Aggregation

They are used to perform some aggregation operations on CQL Query results.

3

Relationship

They are used to get details of relationships such as startnode, endnode, etc.

在后续章节中，我们将详细讨论所有 Neo4j CQL 命令、子句和函数的语法、用法和示例。

We will discuss all Neo4j CQL commands, clauses and functions syntax, usage and examples in-detail in the subsequent chapters.

Neo4j CQL Data Types

这些数据类型类似于 Java 语言。它们用于定义节点或关系的属性。

These data types are similar to Java language. They are used to define properties of a node or a relationship.

Neo4j CQL 支持以下数据类型 −

Neo4j CQL supports the following data types −

Sr.No

CQL Data Type

Usage

1

Boolean

It is used to represent Boolean literals: true, false.

2

byte

It is used to represent 8-bit integers.

3

short

It is used to represent 16-bit integers.

4

int

It is used to represent 32-bit integers.

5

long

It is used to represent 64-bit integers.

6

float

It is used to represent 32-bit floating-point numbers.

7

double

It is used to represent 64-bit floating-point numbers.

8

char

It is used to represent 16-bit characters.

9

String

It is used to represent Strings.

CQL Operators

以下列出了 Neo4j Cypher 查询语言支持的操作符。

Following are the list of operators supported by Neo4j Cypher Query language.

Sr.No

Type

Operators

1

Mathematical

+, -, *, /, %, ^

2

Comparison

+, <>, <, >, ⇐, >=

3

Boolean

AND, OR, XOR, NOT

4

String

+

5

List

+, IN, [X], [X…..Y]

6

Regular Expression

=-

7

String matching

STARTS WITH, ENDS WITH, CONSTRAINTS

Boolean Operators in Neo4j CQL

Neo4j 支持使用 Neo4j CQL WHERE 子句中的以下布尔运算符来支持多个条件。

Neo4j supports the following Boolean operators to use in Neo4j CQL WHERE clause to support multiple conditions.

Sr.No

Boolean Operators

Description

1

AND

It is a Neo4j CQL keyword to support AND operation. It is like SQL AND operator.

2

OR

It is a Neo4j CQL keyword to support OR operation. It is like SQL AND operator.

3

NOT

It is a Neo4j CQL keyword to support NOT operation. It is like SQL AND operator.

4

XOR

It is a Neo4j CQL keyword to support XOR operation. It is like SQL AND operator.

Comparison Operators in Neo4j CQL

Neo4j 支持在 Neo4j CQL WHERE 子句中使用以下比较运算符，以支持条件。

Neo4j supports the following Comparison operators to use in Neo4j CQL WHERE clause to support conditions.

Sr.No

Boolean Operators

Description

1

=

It is a Neo4j CQL "Equal To" operator.

2

<

It is a Neo4j CQL "Not Equal To" operator.

3

<

It is a Neo4j CQL "Less Than" operator.

4

>

It is a Neo4j CQL "Greater Than" operator.

5

⇐

It is a Neo4j CQL "Less Than Or Equal To" operator.

6

> =

It is a Neo4j CQL "Greater Than Or Equal To" operator.