比较两个表并得到不同的打印输出

Question

我的 MySQL 中有两个 table 在列方面完全相同，我们可以称它们为 id、名称、路径、日期。现在我想对这两个 table 进行比较，以便了解 table 1 与 table 2 的不同之处以及 table 2 与 [=17= 的不同之处] 1. 我只想在我的 Java 程序中打印它，现在一个简单的 System.out.print 差值就完美了。

我只想检查两个 table 中名称列中条目的差异。非常感谢任何帮助！

Answer 1

这将连接 id 上的 2 个表并显示名称不同的行：

select a.name, b.name 
from table1 a 
join table2 b on a.id = b.id
where a.name <> b.name

Answer 2

我确定您可以区分两个数据库并查看它们之间的差异，例如（测试数据库和生产数据库）

这是文档

https://dev.mysql.com/doc/mysql-utilities/1.5/en/mysqldbcompare.html

Answer 3

如果您只想查看表 1 中存在但表 2 中不存在的名称列表，请尝试以下操作：

SELECT a.name
FROM table1 a
LEFT JOIN table2 b ON a.name = b.name
WHERE table2.name IS NULL

在该查询中交换表 1 和表 2 以获得表 2 中不匹配的名称。

Answer 4

正确，应该接受。

这里是示例 Java JDBC 代码，展示了他的 SQL 代码的实际应用。我不使用 MySQL （如问题中所示）。相反，此示例使用 H2 Database Engine，创建临时内存数据库。

try {
    Class.forName ( "org.h2.Driver" );
} catch ( final ClassNotFoundException e ) {
    e.printStackTrace ( );
}
try ( Connection conn = DriverManager.getConnection ( "jdbc:h2:mem:trash_me_db" ) ;
      Statement stmt = conn.createStatement ( ) ) {
    String sql = null;

    // Table 1
    sql = "CREATE TABLE t1_ (\n" +
            "  id_ INT IDENTITY ,\n" +
            "  name_ VARCHAR \n" +
            ");";
    stmt.executeUpdate ( sql );
    stmt.execute ( "INSERT INTO t1_ ( name_ ) VALUES ('Jesse');" );
    stmt.execute ( "INSERT INTO t1_ ( name_ ) VALUES ('Wendy');" );
    stmt.execute ( "INSERT INTO t1_ ( name_ ) VALUES ('Lisa');" );
    stmt.execute ( "INSERT INTO t1_ ( name_ ) VALUES ('Susan');" );
    stmt.execute ( "INSERT INTO t1_ ( name_ ) VALUES ('Jimmy');" );
    stmt.execute ( "INSERT INTO t1_ ( name_ ) VALUES ('Wine');" );

    // Dump
    System.out.println ( "\nDump table t1_" );
    try ( ResultSet rs = stmt.executeQuery ( "SELECT * FROM t1_ ;" ) ) {
        while ( rs.next ( ) ) {
            final int id = rs.getInt ( "id_" );    //Retrieve by column name
            final String name = rs.getString ( "name_" );
            System.out.println ( "id: " + id + " | name: " + name );
        }
    }

    // Table 2
    sql = "CREATE TABLE t2_ (\n" +
            "  id_ INT IDENTITY ,\n" +
            "  name_ VARCHAR \n" +
            ");";
    stmt.executeUpdate ( sql );
    stmt.execute ( "INSERT INTO t2_ ( name_ ) VALUES ('Jesse');" );
    stmt.execute ( "INSERT INTO t2_ ( name_ ) VALUES ('Wendy');" );
    stmt.execute ( "INSERT INTO t2_ ( name_ ) VALUES ('Lisa');" );
    stmt.execute ( "INSERT INTO t2_ ( name_ ) VALUES ('Susan');" );
    stmt.execute ( "INSERT INTO t2_ ( name_ ) VALUES ('Jimmy');" );
    stmt.execute ( "INSERT INTO t2_ ( name_ ) VALUES ('Beer');" );

    // Dump
    System.out.println ( "\nDump table t2_" );
    try ( ResultSet rs = stmt.executeQuery ( "SELECT * FROM t2_ ;" ) ) {
        while ( rs.next ( ) ) {
            final int id = rs.getInt ( "id_" );    //Retrieve by column name
            final String name = rs.getString ( "name_" );
            System.out.println ( "id: " + id + " | name: " + name );
        }
    }

    // Difference, left.
    System.out.println ( "\nShow names that exist in t1_ but not in t2_." );
    sql = "SELECT *\n" +
            "FROM t1_ \n" +
            "LEFT JOIN t2_ ON t1_.name_ = t2_.name_\n" +
            "WHERE t2_.name_ IS NULL";
    try ( ResultSet rs = stmt.executeQuery ( sql ) ) {
        while ( rs.next ( ) ) {
            final int id = rs.getInt ( "id_" );    //Retrieve by column name
            final String name = rs.getString ( "name_" );
            System.out.println ( "id: " + id + " | name: " + name );
        }
    }

    // Difference, right.
    System.out.println ( "\nShow names that exist in t2_ but not in t1_." );
    sql = "SELECT *\n" +
            "FROM t2_ \n" +
            "LEFT JOIN t1_ ON t2_.name_ = t1_.name_\n" +
            "WHERE t1_.name_ IS NULL";
    try ( ResultSet rs = stmt.executeQuery ( sql ) ) {
        while ( rs.next ( ) ) {
            final int id = rs.getInt ( "id_" );    //Retrieve by column name
            final String name = rs.getString ( "name_" );
            System.out.println ( "id: " + id + " | name: " + name );
        }
    }


} catch ( final SQLException e ) {
    e.printStackTrace ( );
}

当运行.

Dump table t1_
id: 1 | name: Jesse
id: 2 | name: Wendy
id: 3 | name: Lisa
id: 4 | name: Susan
id: 5 | name: Jimmy
id: 6 | name: Wine

Dump table t2_
id: 1 | name: Jesse
id: 2 | name: Wendy
id: 3 | name: Lisa
id: 4 | name: Susan
id: 5 | name: Jimmy
id: 6 | name: Beer

Show names that exist in t1_ but not in t2_.
id: 6 | name: Wine

Show names that exist in t2_ but not in t1_.
id: 6 | name: Beer

比较两个表并得到不同的打印输出

Compare two tables with each other and get difference printout

java

mysql

sql

database

diff