jdbc知识

Posted 2020-09-14 艺海浮台

C/S

client / server
Socket / ServerSocket
用户体验.

B/S

browser    / server.
ie|firefox / web server.(tomcat)

SQL

structure query language.
insert into t(f1,f2,...) values(v1,v2,...) ;
delete from t where ...
update t set f1=v1,f2=v2 ,... where ...
select * from t ;
select id,name,... from t ;     //projection,投影查询

JDBC

java database connection.
java数据库连接
规范(接口)。
Driver          //驱动程序
driverclass     //com.mysql.jdbc.Driver
url             //jdbc:mysql://localhost:3306/big3
username        //root
password        //root

Class.forName("com.mysql.jdbc.Driver");     //
conn = DriverManager.getConnection(...);    //
Statement st = conn.createStatement();      //语句
st.execute("delete from users where id < 4");//
st.close();

sql

select * from users order by id desc ;                      //默认asc     
select * from users order by id asc,name desc,age asc ;     //
select * from users order by 1 asc,2 desc,3 asc ;           //

事务性

Transaction:事务
            commit          //提交
            rollback        //回滚.
和db之间一组操作。
四个特性acid:

atomic      //原子性,不可分割.同时成功或同时失败
consistent  //一致性,数据执行前后不能破坏掉.
isolate     //隔离型,事务独立的。
durable     //永久性,永久有效.

jdbc的事务处理

conn.setAutocommit(false);      //关闭自动提交

conn.commit();                  //提交事务

conn.rollback(SavePoint sp);    //回滚事务

聚集函数查询

select count(1) from users;

查询mysql的系统表

//查询指定的库中是否含有指定的表,通过查询系统库实现的。
select table_name from information_schema.tables where table_name = ‘users‘ and table_schema = ‘big3‘;

use 

[DDL]
create 
drop
alter

分页查询

mysql:          //limit
                //                 3:offset, 10:length
                //select ... limit 3,10;
oracle:         //嵌套子查询rownum
sqlserver       //top

修改表

alter table users add column password varchar(20);
desc users;
update users set password = ‘123456‘ ;

sql注入:
-------------
select * from users where name = ‘tom0‘ and password=‘123456‘


Statement
-----------------
    执行静态语句.
    导致sql注入问题。

PreparedStatement
-----------------

截断表,数据无法回滚。

truncate table users;

Statement < PreparedStatement < CallableStatement

LOB:large Object.

MySQL

LongBlob        //long binary large object.
Text            //

操作大对象

1.增加两个字段
    alter table users add column pic longblob ;
    alter table users add column info text ;
    //
    conn = getConn();           //连接
    conn.setAutoCommit(false);  //自动提交
    String sql = "select pic from users where id = ?" ;
    ppst = conn.prepareStatement(sql);
    ppst.setInt(1,1);
    ResultSet rs = ppst.executeQuery();
    if(rs.next()){
        byte[] bytes = rs.getBytes(1);
        FileOutputStream fos = new FileOutputStream("d:/KKK.jpg");
        fos.write(bytes);
        fos.close();
    }

    conn.commit();
    ppst.close();
    conn.close();

mysql赋值语法

1.set x := a + b ;

2.select count(*) into x from ... ;

存储过程

1.创建add存储过程
    mysql>delimiter //
    mysql>create procedure up_add(in a int,in b int ,out c int)
    mysql>begin
    mysql>set c := a + b ;
    mysql>end 
    mysql>//

    mysql>call up_add(1,2,@x) //
    mysql>select @x //

2.java调用存储过程
    Connection conn = null ;
    CallableStatement cst = null ;
    try {
        conn = getConn();           //连接
        cst  = conn.prepareCall("{call up_add(?,?,?)}");
        cst.setInt(1, 1);
        cst.setInt(2, 3);
        cst.registerOutParameter(3, Types.INTEGER);
        //执行存储过程
        cst.execute();
        int r = cst.getInt(3);
        System.out.println(r);

        cst.close();
        conn.close();
    } catch (Exception e) {
        e.printStackTrace();
    }

3.处理游标

    CREATE PROCEDURE curdemo()
    BEGIN
      DECLARE done INT DEFAULT 0;
      DECLARE a CHAR(16);
      DECLARE b,c INT;
      DECLARE cur1 CURSOR FOR SELECT id,data FROM test.t1;
      DECLARE cur2 CURSOR FOR SELECT i FROM test.t2;
      DECLARE CONTINUE HANDLER FOR SQLSTATE ‘02000‘ SET done = 1;

      OPEN cur1;
      OPEN cur2;

      REPEAT
        FETCH cur1 INTO a, b;
        FETCH cur2 INTO c;
        IF NOT done THEN
           IF b < c THEN
              INSERT INTO test.t3 VALUES (a,b);
           ELSE
              INSERT INTO test.t3 VALUES (a,c);
           END IF;
        END IF;
      UNTIL done END REPEAT;

      CLOSE cur1;
      CLOSE cur2;
    END

通过存储过程实现百万记录插入

1.创建存储过程
    create procedure up_biginsert(in num int)
    begin
        declare i int default 0;
        start transaction ;
        while i < num do
            insert into users(name,password,age) values(concat(‘tom‘,i),concat(‘‘,i),i % 30);
            set i := i + 1 ;
        end while ;
        commit ;
    end

2.java代码
    Connection conn = null ;
    CallableStatement cst = null ;
    try {
        conn = getConn();           //连接
        long start = System.currentTimeMillis() ;
        cst  = conn.prepareCall("{call up_biginsert(?)}");
        cst.setInt(1, 1000000);
        //执行存储过程
        cst.execute();
        System.out.println(System.currentTimeMillis() - start);
        cst.close();
        conn.close();
    } catch (Exception e) {
        e.printStackTrace();
    }

3.java执行DDL语句.
    Connection conn = null ;
    try {
        conn = getConn();           //连接
        long start = System.currentTimeMillis() ;
        //删除过程
        conn.prepareStatement("drop procedure up_biginsert").executeUpdate();
        System.out.println(System.currentTimeMillis() - start);
        conn.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
    查看存储过程 show procedure status //
    查看存储过程的定义： show create procedure my_add //

MySQL函数,有返回值

1.创建函数
    mysql>create function uf_add(a int, b int) returns int return a + b ; //
2.java
    Connection conn = null ;
    CallableStatement cst = null ;
    try {
        conn = getConn();           //连接
        long start = System.currentTimeMillis() ;
        cas=conn.prepareCall("{?=call uf_add(?,?)}");
        cas.registerOutParameter(1,Types.INTEGER);
        cst.setInt(2,1);
        cas.setInt(3,2);
        //执行存储过程
        cst.execute();
        Sysout.out.println(cst.getInt(1));
        System.out.println(System.currentTimeMillis() - start);
        cst.close();
        conn.close();
    } catch (Exception e) {
        e.printStackTrace();
    }