aws(学习笔记第十四课) 面向NoSQL DB的DynamoDB

aws(学习笔记第十四课)

  • 面向NoSQL DBDynamoDB

学习内容:

  • 开发一个任务TODO管理器

1. 主键,分区键和排序键

  1. DynamoDB的表定义和属性定义
    • 表定义(简单主键)
      • 表定义的命名需要系统名 + _ + 表名的形式,提前规划好前缀。因为DynamoDB直接建立表,没有建立数据库,之后在个别的数据库里面建立表的过程,所以注意提前规划。

      • 分区键 -简单的主键,由一个称为分区键 的属性组成。DynamoDB 使用分区键的值作为内部散列函数的输入。来自散列函数的输出决定了项目将存储到的分区 (DynamoDB 内部的物理存储)。在只有分区键的表中,任何两个项目都不能有相同的分区键值

      • 表定义代码
        注意,建表语句区分大小写
        注意,这里建表的时候,建表的时候id作为主键,不参与主键的namegender不能定义

        shell 复制代码
        aws dynamodb create-table --table-name stu_system_student \
        --attribute-definitions AttributeName=id,AttributeType=S \
        --key-schema AttributeName=id,KeyType=HASH \
        --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

        定义之后如下所示:

        shell 复制代码
        $ aws dynamodb create-table --table-name stu_system_student \
        --attribute-definitions AttributeName=id,AttributeType=S \
        --key-schema AttributeName=id,KeyType=HASH \
        --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5
        {
            "TableDescription": {
                "AttributeDefinitions": [
                    {
                        "AttributeName": "id",
                        "AttributeType": "S"
                    }
                ],
                "TableName": "stu_system_student",
                "KeySchema": [
                    {
                        "AttributeName": "id",
                        "KeyType": "HASH"
                    }
                ],
                "TableStatus": "CREATING",
                "CreationDateTime": "2024-11-16T16:37:57.967000+08:00",
                "ProvisionedThroughput": {
                    "NumberOfDecreasesToday": 0,
                    "ReadCapacityUnits": 5,
                    "WriteCapacityUnits": 5
                },
                "TableSizeBytes": 0,
                "ItemCount": 0,
                "TableArn": "arn:aws:dynamodb:ap-northeast-1:081353481087:table/stu_system_student",
                "TableId": "316d0a81-801b-451a-8fe1-57959f1906c6",
                "DeletionProtectionEnabled": false
            }
        }

        执行aws cli查看表建立的状态

        shell 复制代码
        $ aws dynamodb describe-table --table-name stu_system_student
        {
            "Table": {
                "AttributeDefinitions": [
                    {
                        "AttributeName": "id",
                        "AttributeType": "S"
                    }
                ],
                "TableName": "stu_system_student",
                "KeySchema": [
                    {
                        "AttributeName": "id",
                        "KeyType": "HASH"
                    }
                ],
                "TableStatus": "ACTIVE",
                "CreationDateTime": "2024-11-16T16:37:57.967000+08:00",
                "ProvisionedThroughput": {
                    "NumberOfDecreasesToday": 0,
                    "ReadCapacityUnits": 5,
                    "WriteCapacityUnits": 5
                },
                "TableSizeBytes": 0,
                "ItemCount": 0,
                "TableArn": "arn:aws:dynamodb:ap-northeast-1:081353481087:table/stu_system_student",
                "TableId": "316d0a81-801b-451a-8fe1-57959f1906c6",
                "DeletionProtectionEnabled": false
            }
        }
    • 表定义(复合主键)
      • 分区键和排序键 - 称为复合主键,此类型的键由两个属性组成。第一个属性是分区键,第二个属性是排序键。

      • DynamoDB 使用分区键值作为对内部散列函数的输入。来自散列函数的输出决定了项目将存储到的分区 (DynamoDB 内部的物理存储)。具有相同分区键的所有项目按排序键值的排序顺序存储在一起。

      • 在具有分区键和排序键的表中,两个项目可以具有相同的分区键值,但是,这两个项目必须具有不同的排序键值。

      • 定义复合主键表

        shell 复制代码
        aws dynamodb create-table --table-name stu_system_score \
        --attribute-definitions AttributeName=id,AttributeType=S \
        AttributeName=lesson,AttributeType=S \
        --key-schema AttributeName=id,KeyType=HASH \
        AttributeName=lesson,KeyType=RANGE \
        --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5
      • 复合建表结果

        shell 复制代码
        $ aws dynamodb create-table --table-name stu_system_score \
        --attribute-definitions AttributeName=id,AttributeType=S \
        AttributeName=lesson,AttributeType=S \
        --key-schema AttributeName=id,KeyType=HASH \
        AttributeName=lesson,KeyType=RANGE \
        --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5
        {
            "TableDescription": {
                "AttributeDefinitions": [
                    {
                        "AttributeName": "id",
                        "AttributeType": "S"
                    },
                    {
                        "AttributeName": "lesson",
                        "AttributeType": "S"
                    }
                ],
                "TableName": "stu_system_score",
                "KeySchema": [
                    {
                        "AttributeName": "id",
                        "KeyType": "HASH"
                    },
                    {
                        "AttributeName": "lesson",
                        "KeyType": "RANGE"
                    }
                ],
                "TableStatus": "CREATING",
                "CreationDateTime": "2024-11-16T16:55:16.830000+08:00",
                "ProvisionedThroughput": {
                    "NumberOfDecreasesToday": 0,
                    "ReadCapacityUnits": 5,
                    "WriteCapacityUnits": 5
                },
                "TableSizeBytes": 0,
                "ItemCount": 0,
                "TableArn": "arn:aws:dynamodb:ap-northeast-1:081353481087:table/stu_system_score",
                "TableId": "795a7ce6-8ecf-46c8-90f7-5c31e615886f",
                "DeletionProtectionEnabled": false
            }
        }

        这里,AttributeName=id这个属性是分区键,不是主键。AttributeName=lesson这个属性是排序键,他们两个属性组成联合主键。

2. 利用DynamoDB编写一个任务管理器的例子

3. 创建表

  1. 创建两个表todo-usertodo-task
    • todo-user

      shell 复制代码
      aws dynamodb create-table --table-name todo-user \
      --attribute-definitions AttributeName=uid,AttributeType=S \
      --key-schema AttributeName=uid,KeyType=HASH \
      --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5
    • todo-task

      shell 复制代码
      aws dynamodb create-table --table-name todo-task \
      --attribute-definitions AttributeName=uid,AttributeType=S \
      AttributeName=tid,AttributeType=N \
      --key-schema AttributeName=uid,KeyType=HASH \
      AttributeName=tid,KeyType=RANGE \
      --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

4. docopt命令行代码框架以及node整体程序

  1. docoptcli模板文件

    shell 复制代码
    nodetodo
    
    Usage:
      nodetodo user-add <uid> <email> <phone>
      nodetodo user-rm <uid>
      nodetodo user-ls [--limit=<limit>] [--next=<id>]
      nodetodo user <uid>
      nodetodo task-add <uid> <description> [<category>] [--dueat=<yyyymmdd>] 
      nodetodo task-rm <uid> <tid>
      nodetodo task-ls <uid> [<category>] [--overdue|--due|--withoutdue|--futuredue|--dueafter=<yyyymmdd>|--duebefore=<yyyymmdd>] [--limit=<limit>] [--next=<id>]
      nodetodo task-la <category> [--overdue|--due|--withoutdue|--futuredue|--dueafter=<yyyymmdd>|--duebefore=<yyyymmdd>] [--limit=<limit>] [--next=<id>]
      nodetodo task-done <uid> <tid>
      nodetodo -h | --help
      nodetodo --version
    
    Options:
      -h --help        Show this screen.
      --version        Show version.
      --limit=<limit>  Maximum number of results [default: 10].
  2. node程序todo-task的整体结构

    • 整体代码

      node 复制代码
      var fs = require('fs');
      var docopt = require('docopt');
      var moment = require("moment");
      var AWS = require('aws-sdk');
      var db = new AWS.DynamoDB({
      	"region": "ap-northeast-1"
      });
      
      var cli = fs.readFileSync('./cli.txt', {"encoding": "utf8"});
      var input = docopt.docopt(cli, {"version": "1.0", "argv": process.argv.splice(2)});
      
      function getValue(attribute, type) {
      	if (attribute === undefined) {
      		return null;
      	}
      	return attribute[type];
      }
      
      function mapTaskItem(item) {
      	return {
      		"tid": item.tid.N,
      		"description": item.description.S,
      		"created": item.created.N,
      		"due": getValue(item.due, 'N'),
      		"category": getValue(item.category, 'S'),
      		"completed": getValue(item.completed, 'N')
      	};
      }
      
      function mapUserItem(item) {
      	return {
      		"uid": item.uid.S,
      		"email": item.email.S,
      		"phone": item.phone.S
      	};
      }
      
      if (input['user-add'] === true) {
      	var params = {
      		"Item": {
      			"uid": {
      				"S": input['<uid>']
      			},
      			"email": {
      				"S": input['<email>']
      			},
      			"phone": {
      				"S": input['<phone>']
      			}
      		},
      		"TableName": "todo-user",
      		"ConditionExpression": "attribute_not_exists(uid)"
      	};
      	db.putItem(params, function(err) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('user added with uid ' + input['<uid>']);
      		}
      	});
      } else if (input['user-rm'] === true) {
      	var params = {
      		"Key": {
      			"uid": {
      				"S": input['<uid>']
      			}
      		},
      		"TableName": "todo-user"
      	};
      	db.deleteItem(params, function(err) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('user removed with uid ' + input['<uid>']);
      		}
      	});
      } else if (input['user-ls'] === true) {
      	var params = {
      		"TableName": "todo-user",
      		"Limit": input['--limit']
      	};
      	if (input['--next'] !== null) {
      		params.ExclusiveStartKey = {
      			"uid": {
      				"S": input['--next']
      			}
      		};
      	}
      	db.scan(params, function(err, data) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('users', data.Items.map(mapUserItem));
      			if (data.LastEvaluatedKey !== undefined) {
      				console.log('more users available with --next=' + data.LastEvaluatedKey.uid.S);
      			}
      		}
      	});
      } else if (input['user'] === true) {
      	var params = {
      		"Key": {
      			"uid": {
      				"S": input['<uid>']
      			}
      		},
      		"TableName": "todo-user"
      	};
      	db.getItem(params, function(err, data) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			if (data.Item) {
      				console.log('user with uid ' + input['<uid>'], mapUserItem(data.Item));
      			} else {
      				console.error('user with uid ' + input['<uid>'] + ' not found');
      			}
      		}
      	});
      } else if (input['task-add'] === true) {
      	var tid = Date.now();
      	var params = {
      		"Item": {
      			"uid": {
      				"S": input['<uid>']
      			},
      			"tid": {
      				"N": tid.toString()
      			},
      			"description": {
      				"S": input['<description>']
      			},
      			"created": {
      				"N": moment().format("YYYYMMDD")
      			}
      		},
      		"TableName": "todo-task",
      		"ConditionExpression": "attribute_not_exists(uid) and attribute_not_exists(tid)"
      	};
      	if (input['--dueat'] !== null) {
      		params.Item.due = {
      			"N": input['--dueat']
      		};
      	}
      	if (input['<category>'] !== null) {
      		params.Item.category = {
      			"S": input['<category>']
      		};
      	}
      	db.putItem(params, function(err) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('task added with tid ' + tid);
      		}
      	});
      } else if (input['task-rm'] === true) {
      	var params = {
      		"Key": {
      			"uid": {
      				"S": input['<uid>']
      			},
      			"tid": {
      				"N": input['<tid>']
      			}
      		},
      		"TableName": "todo-task"
      	};
      	db.deleteItem(params, function(err) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('task removed with tid ' + input['<tid>']);
      		}
      	});
      } else if (input['task-ls'] === true) {
      	var params = {
      		"KeyConditionExpression": "uid = :uid",
      		"ExpressionAttributeValues": {
      			":uid": {
      				"S": input['<uid>']
      			}
      		},
      		"TableName": "todo-task",
      		"Limit": input['--limit']
      	};
      	if (input['--next'] !== null) {
      		params.KeyConditionExpression += ' AND tid > :next';
      		params.ExpressionAttributeValues[':next'] = {
      			"N": input['--next']
      		};
      	}
      	if (input['--overdue'] === true) {
      		params.FilterExpression = "due < :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--due'] === true) {
      		params.FilterExpression = "due = :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--withoutdue'] === true) {
      		params.FilterExpression = "attribute_not_exists(due)";
      	} else if (input['--futuredue'] === true) {
      		params.FilterExpression = "due > :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--dueafter'] !== null) {
      		params.FilterExpression = "due > :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": input['--dueafter']};
      	} else if (input['--duebefore'] !== null) {
      		params.FilterExpression = "due < :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": input['--duebefore']};
      	}
      	if (input['<category>'] !== null) {
      		if (params.FilterExpression === undefined) {
      			params.FilterExpression = '';
      		} else {
      			params.FilterExpression += ' AND ';
      		}
      		params.FilterExpression += 'category = :category';
      		params.ExpressionAttributeValues[':category'] = {
      			"S": input['<category>']
      		};
      	}
      	db.query(params, function(err, data) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('tasks', data.Items.map(mapTaskItem));
      			if (data.LastEvaluatedKey !== undefined) {
      				console.log('more tasks available with --next=' + data.LastEvaluatedKey.tid.N);
      			}
      		}
      	});
      } else if (input['task-la'] === true) {
      	var params = {
      		"KeyConditionExpression": "category = :category",
      		"ExpressionAttributeValues": {
      			":category": {
      				"S": input['<category>']
      			}
      		},
      		"TableName": "todo-task",
      		"IndexName": "category-index",
      		"Limit": input['--limit']
      	};
      	if (input['--next'] !== null) {
      		params.KeyConditionExpression += ' AND tid > :next';
      		params.ExpressionAttributeValues[':next'] = {
      			"N": input['--next']
      		};
      	}
      	if (input['--overdue'] === true) {
      		params.FilterExpression = "due < :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--due'] === true) {
      		params.FilterExpression = "due = :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--withoutdue'] === true) {
      		params.FilterExpression = "attribute_not_exists(due)";
      	} else if (input['--futuredue'] === true) {
      		params.FilterExpression = "due > :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--dueafter'] !== null) {
      		params.FilterExpression = "due > :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": input['--dueafter']};
      	} else if (input['--duebefore'] !== null) {
      		params.FilterExpression = "due < :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": input['--duebefore']};
      	}
      	db.query(params, function(err, data) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('tasks', data.Items.map(mapTaskItem));
      			if (data.LastEvaluatedKey !== undefined) {
      				console.log('more tasks available with --next=' + data.LastEvaluatedKey.tid.N);
      			}
      		}
      	});
      } else if (input['task-done'] === true) {
      	var params = {
      		"Key": {
      			"uid": {
      				"S": input['<uid>']
      			},
      			"tid": {
      				"N": input['<tid>']
      			}
      		},
      		"UpdateExpression": "SET completed = :yyyymmdd",
      		"ExpressionAttributeValues": {
      			":yyyymmdd": {
      				"N": moment().format("YYYYMMDD")
      			}
      		},
      		"TableName": "todo-task"
      	};
      	db.updateItem(params, function(err) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('task completed with tid ' + input['<tid>']);
      		}
      	});
      }

5. 进行操作以及代码解析

  1. 增加用户

    • 命令执行

      shell 复制代码
      node index.js user-add '001' 'finlay@163.com' '1234567'
    • 实现代码

      javascript 复制代码
      	var params = {
      		"Item": {
      			"uid": {
      				"S": input['<uid>']
      			},
      			"email": {
      				"S": input['<email>']
      			},
      			"phone": {
      				"S": input['<phone>']
      			}
      		},
      		"TableName": "todo-user",
      		"ConditionExpression": "attribute_not_exists(uid)"
      	};
  2. 查询用户

    • 执行命令

      shell 复制代码
       node index.js user-ls
    • 实现代码

      javascript 复制代码
      } else if (input['user-ls'] === true) {
      	var params = {
      		"TableName": "todo-user",
      		"Limit": input['--limit']
      	};
      	if (input['--next'] !== null) {
      		params.ExclusiveStartKey = {
      			"uid": {
      				"S": input['--next']
      			}
      		};
      	}
      	db.scan(params, function(err, data) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('users', data.Items.map(mapUserItem));
      			if (data.LastEvaluatedKey !== undefined) {
      				console.log('more users available with --next=' + data.LastEvaluatedKey.uid.S);
      			}
      		}
      	});

6. 查询用户表数据

  1. 执行查询用户命令
    • 查询用户

      shell 复制代码
      $ node index.js user-ls
      users [ { uid: '001', email: 'finlay@163.com', phone: '13512345678' } ]
    • 实现代码

      javascript 复制代码
      } else if (input['user-ls'] === true) {
      	var params = {
      		"TableName": "todo-user",
      		"Limit": input['--limit']
      	};
      	if (input['--next'] !== null) {
      		params.ExclusiveStartKey = {
      			"uid": {
      				"S": input['--next']
      			}
      		};
      	}
      	db.scan(params, function(err, data) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('users', data.Items.map(mapUserItem));
      			if (data.LastEvaluatedKey !== undefined) {
      				console.log('more users available with --next=' + data.LastEvaluatedKey.uid.S);
      			}
      		}
      	});

7. 追加task表数据

  1. 执行追加命令
    • 执行追加task命令

      shell 复制代码
      node index.js task-add 001 "this is a emergency job" --dueat=20241201
    • 实现代码

      javascript 复制代码
      } else if (input['task-add'] === true) {
      	var tid = Date.now();
      	var params = {
      		"Item": {
      			"uid": {
      				"S": input['<uid>']
      			},
      			"tid": {
      				"N": tid.toString()
      			},
      			"description": {
      				"S": input['<description>']
      			},
      			"created": {
      				"N": moment().format("YYYYMMDD")
      			}
      		},
      		"TableName": "todo-task",
      		"ConditionExpression": "attribute_not_exists(uid) and attribute_not_exists(tid)"
      	};
      	if (input['--dueat'] !== null) {
      		params.Item.due = {
      			"N": input['--dueat']
      		};
      	}
      	if (input['<category>'] !== null) {
      		params.Item.category = {
      			"S": input['<category>']
      		};
      	}
      	db.putItem(params, function(err) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('task added with tid ' + tid);
      		}
      	});

8. 查询task表数据

  1. 执行task查询命令
    • 执行查询task命令

      shell 复制代码
      node index.js task-ls 001
    • 代码实现

      javascript 复制代码
      } else if (input['task-ls'] === true) {
      	var params = {
      		"KeyConditionExpression": "uid = :uid",
      		"ExpressionAttributeValues": {
      			":uid": {
      				"S": input['<uid>']
      			}
      		},
      		"TableName": "todo-task",
      		"Limit": input['--limit']
      	};
      	if (input['--next'] !== null) {
      		params.KeyConditionExpression += ' AND tid > :next';
      		params.ExpressionAttributeValues[':next'] = {
      			"N": input['--next']
      		};
      	}
      	if (input['--overdue'] === true) {
      		params.FilterExpression = "due < :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--due'] === true) {
      		params.FilterExpression = "due = :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--withoutdue'] === true) {
      		params.FilterExpression = "attribute_not_exists(due)";
      	} else if (input['--futuredue'] === true) {
      		params.FilterExpression = "due > :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": moment().format("YYYYMMDD")};
      	} else if (input['--dueafter'] !== null) {
      		params.FilterExpression = "due > :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": input['--dueafter']};
      	} else if (input['--duebefore'] !== null) {
      		params.FilterExpression = "due < :yyyymmdd";
      		params.ExpressionAttributeValues[':yyyymmdd'] = {"N": input['--duebefore']};
      	}
      	if (input['<category>'] !== null) {
      		if (params.FilterExpression === undefined) {
      			params.FilterExpression = '';
      		} else {
      			params.FilterExpression += ' AND ';
      		}
      		params.FilterExpression += 'category = :category';
      		params.ExpressionAttributeValues[':category'] = {
      			"S": input['<category>']
      		};
      	}
      	db.query(params, function(err, data) {
      		if (err) {
      			console.error('error', err);
      		} else {
      			console.log('tasks', data.Items.map(mapTaskItem));
      			if (data.LastEvaluatedKey !== undefined) {
      				console.log('more tasks available with --next=' + data.LastEvaluatedKey.tid.N);
      			}
      		}
      	});

9. 查询表数据的三种方式

  1. 提供键来获取数据

    • 指定主键的属性

    • 使用分区键加上过滤条件查询

  2. 二级索引查询

    • 二级索引的原理
      下面的例子category作为索引的例子,通过再做出一个索引表,DynamoDB增加一个原表的另一个只读索引表。

    • 作成二级索引
      注意,json如果在命令行里面,命令行对于json这里就不能使用\换行符!

      shell 复制代码
      aws dynamodb update-table --table-name todo-task \
      --attribute-definitions AttributeName=uid,AttributeType=S \
      AttributeName=tid,AttributeType=N \
      AttributeName=category,AttributeType=S \
      --global-secondary-index-updates '[{"Create": {"IndexName": "category-index","KeySchema":[{"AttributeName":"category","KeyType":"HASH"},{"AttributeName": "tid", "KeyType": "RANGE"}],"Projection": {"ProjectionType": "ALL"},"ProvisionedThroughput":{"ReadCapacityUnits":5,"WriteCapacityUnits":5}}}]'
  1. 扫描查询
    如果实在没有主键,分区键,排序键进行查找,那么选择full table scan也是没有办法的事情。
相关推荐
hefaxiang6 分钟前
【Mysql】Mysql的多表查询---多表联合查询(中)
数据库·mysql
运维之美@7 分钟前
mysql数据迁移PolarDB
数据库·mysql
破浪前行·吴8 分钟前
【学习】【HTML】localStorage、sessionStorage、cookie
前端·学习·html
Natural_yz11 分钟前
大数据学习15之Scala集合与泛型
开发语言·学习·scala
知识的宝藏32 分钟前
Django数据写入MySQL数据库
数据库·mysql·django
L_cl1 小时前
Python学习从0到1 day28 Python 高阶技巧 ⑥ Socket服务端开发
运维·服务器·学习
刘艳兵的学习博客1 小时前
刘艳兵-DBA038-以下关于Oracle SGA和PGA的描述中,哪些是正确的?
服务器·数据库·oracle·面试·刘艳兵
我叫汪枫1 小时前
吉林大学 超星慕课 高级语言程序设计 学习通部分题目极其答案
数据结构·学习·算法
MXsoft6181 小时前
浪潮服务器(BMC)监控易监测指标解读
大数据·运维·数据库
小小宇宙中微子1 小时前
简单理解回调函数
linux·服务器·数据库