# tail -10f /var/log/mongodb/mongod.log
2020-07-09T12:20:17.391+0800 I NETWORK [listener] Listening on /tmp/mongodb-27017.sock
2020-07-09T12:20:17.392+0800 I NETWORK [listener] Listening on 127.0.0.1
2020-07-09T12:20:17.392+0800 I NETWORK [listener] waiting for connections on port 27017
MongoDB 后台管理 Shell
如果你需要进入 mongodb 后台管理，你需要先打开 mongodb 装目录的下的 bin 目录，然后执行 mongo 命令文件。
$ cd /usr/local/mongodb4/bin
$ ./mongo
MongoDB shell version v4.2.8
connecting to: mongodb://127.0.0.1:27017/?compressors=disabled&gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("2cfdafc4-dd56-4cfc-933a-187b887119b3") }
MongoDB server version: 4.2.8
Welcome to the MongoDB shell.
……
mysql> select a.*,b.* from a inner join b on a.age=b.ageb; #第一种 inner join
+------+------+-------+------+
| name | age | nameB | ageB |
+------+------+-------+------+
| A1 | 1 | B1 | 1 |
+------+------+-------+------+
1 row in set (0.00 sec)
mysql> select a.*,b.* from a join b on a.age=b.ageb; #第二种 join (默认是inner join)
+------+------+-------+------+
| name | age | nameB | ageB |
+------+------+-------+------+
| A1 | 1 | B1 | 1 |
+------+------+-------+------+
1 row in set (0.00 sec)
三个表的显示内连接:
SELECT
a.*,
b.*,
c.*
FROM exampaper a
INNER JOIN bigquestion b
INNER JOIN exampaperquestion c
ON a.paperId = b.paperId
AND b.bigQuertionId = c.bigQuertionId
四个表的显示内连接:
SELECT
train.trainingSchemaName,
train.majorName,
train.createTime,
tc.*, course.*, type.*
FROM
trainschemeinfo train
JOIN train_course tc ON train.trainingSchemeID = tc.trainningSchemeID
INNER JOIN t_course_base_info course ON tc.courseID = course.courseId
INNER JOIN coursetypeinfo type ON tc.typeNum = type.typeNum
WHERE
tc.trainningSchemeID = '661ecb064b164d1ea133956f89beddb7'
与之等价的隐士内连接:
SELECT
train.trainingSchemaName,
train.majorName,
train.createTime,
tc.*, course.*, type.*
FROM
trainschemeinfo train,
train_course tc,
t_course_base_info course,
coursetypeinfo type
WHERE
train.trainingSchemeID = tc.trainningSchemeID
AND tc.courseID = course.courseId
AND tc.typeNum = type.typeNum
AND tc.trainningSchemeID = '661ecb064b164d1ea133956f89beddb7'
(2)显示内连接带条件
mysql> select a.*,b.* from a join b on a.age=b.ageb having a.name='A1'; #having从查出的数据中挑选满足条件的元祖
+------+------+-------+------+
| name | age | nameB | ageB |
+------+------+-------+------+
| A1 | 1 | B1 | 1 |
+------+------+-------+------+
1 row in set (0.00 sec)
mysql> select a.*,b.* from a join b on a.age=b.ageb where a.name='A1'; #where查询满足条件的元素
+------+------+-------+------+
| name | age | nameB | ageB |
+------+------+-------+------+
| A1 | 1 | B1 | 1 |
+------+------+-------+------+
1 row in set (0.00 sec)
隐士内连接:
mysql> select * from a,b where a.age=b.ageb;
+------+------+-------+------+
| name | age | nameB | ageB |
+------+------+-------+------+
| A1 | 1 | B1 | 1 |
+------+------+-------+------+
1 row in set (0.00 sec)
mysql> select * from a,b where a.age=b.ageb and a.name='A1';
+------+------+-------+------+
| name | age | nameB | ageB |
+------+------+-------+------+
| A1 | 1 | B1 | 1 |
+------+------+-------+------+
1 row in set (0.00 sec)
mysql> select * from a,b where a.age=b.ageb having a.name='A1';
+------+------+-------+------+
| name | age | nameB | ageB |
+------+------+-------+------+
| A1 | 1 | B1 | 1 |
+------+------+-------+------+
1 row in set (0.00 sec)
SELECT
classID AS departNum,
className AS departName,
"class" AS departType,
(SELECT
majorID
FROM t_major_base_info
WHERE majorID = class.majorID) AS updepartNum
FROM t_class_base_info class
UNION
SELECT majorID AS departNum,
majorName AS departName,
"major" AS departType,
(SELECT
collegeID FROM t_college_base_info
WHERE collegeID=major.collegeID) AS updepartNum
FROM t_major_base_info major
UNION
SELECT collegeId AS departNum,
collegeName AS departName,
"college" AS departType,
"000" AS updepartNum
FROM t_college_base_info
(2) union all 保留重复元素
UNION ALL 命令和 UNION 命令几乎是等效的，不过 UNION ALL 命令会列出所有的值。
mysql> select * from a union all select * from b;
+------+------+
| name | age |
+------+------+
| A1 | 1 |
| A2 | 2 |
| B1 | 1 |
| B2 | 22 |
| A1 | 1 |
+------+------+
5 rows in set (0.00 sec)
总结:
UNION 用于合并两个或多个 SELECT 语句的结果集，并消去表中任何重复行。 UNION 内部的 SELECT 语句必须拥有相同数量的列，列也必须拥有相似的数据类型。 同时，每条 SELECT 语句中的列的顺序必须相同.
默认地，UNION 操作符选取不同的值。如果允许重复的值，请使用 UNION ALL。 当 ALL 随 UNION 一起使用时（即 UNION ALL），不消除重复行
public List<Map<String, Object>> getAllData(List<String> tableNames) {
List<String> sqls = new ArrayList();
StringBuilder sb = null;
for (String tableName : tableNames) {
sb = new StringBuilder();
sb.append("select id,name from ");
sb.append(tableName);
sb.append(" where 1=1");
sb.append(" and name = 'zhangsan'");
sqls.add(sb.toString());
}
String sqlFinally = StringUtils.join(sqls, " union ");
sqlFinally += "order by name limit 5,5";
System.out.println(sqlFinally);
/*Session session = getSessionFactory().openSession();
SQLQuery sqlQuery = session.createSQLQuery(sqlFinally);
sqlQuery.setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP);
return sqlQuery.list();*/
return null;
}
测试：
public static void main(String[] args) {
GroupDaoImpl g = new GroupDaoImpl();
List tableNames = new ArrayList();
tableNames.add("t1");
tableNames.add("t2");
tableNames.add("t3");
g.getAllData(tableNames);
}
结果:
select id,name from t1 where 1=1 and name = 'zhangsan' union select id,name from t2 where 1=1 and name = 'zhangsan' union select id,name from t3 where 1=1 and name = 'zhangsan' order by name limit 5,5
class Request extends Thread { public $url; public $response; public function __construct($url) { $this->url = $url; } public function run() { $this->response = file_get_contents($this->url); }}
异步请求
将同步的请求拆分为多个线程异步调用，以提升程序的运行效率。
$chG = new Request("www.google.com");$chB = new Request("www.baidu.com");$chG ->start();$chB ->start();$chG->join();$chB->join(); $gl = $chG->response;$bd = $chB->response;
