从未知数据库 SQL 和 Java 中查找外键

Posted 2023-02-19

【中文标题】从未知数据库 SQL 和 Java 中查找外键

【英文标题】：Finding Foreign Keys From Unknown Database SQL and Java

【发布时间】：2011-04-20 21:18:07

【问题描述】：

我有一个 java 程序，它可以通过任何类型的数据库和任何数量的表进行查询。用户可以输入一个字符串，它将返回包含该字符串的表和行。问题是其中一些表有外键。在事先不了解数据库的情况下，如何递归地遍历所有表以查找外键和行？

平台：Windows 7(64) 数据库类型：Postgres

代码：

public static void connectPostGres(String type, String server, String database, String port, String username, String password) System.out.println("-------- PostgreSQL JDBC连接测试------------"); 尝试 Class.forName("org.postgresql.Driver"); 捕捉（ClassNotFoundException e） System.out.println("您的 PostgreSQL JDBC 驱动程序在哪里？包含在您的库路径中！"); e.printStackTrace(); 返回; System.out.println("PostgreSQL JDBC 驱动注册！"); 连接连接 = null; 尝试 connection = DriverManager.getConnection("jdbc:postgresql://" + server + ":" + port + "/" + 数据库、用户名、密码); //connection = DriverManager.getConnection("*********); 捕捉（SQLException e） System.out.println("doh!"); e.printStackTrace(); 返回; 如果（连接！= null） System.out.println("正在搜索..."); LinkedList allTables = new LinkedList(); 尝试 语句 st = connection.createStatement(); ResultSet rs = st.executeQuery("select * from pg_tables");//获取所有表 而（rs.next（）） String myString = rs.getString("tablename"); if (myString.trim().charAt(0) == 'p' && myString.trim().charAt(1) == 'g') //这只是一些我们不想查询的蹩脚表 else if (myString.trim().charAt(0) == 's' && myString.trim().charAt(1) == 'q' && myString.trim().charAt(2) == 'l ') //这只是一些我们不想查询的蹩脚表 别的 allTables.add(myString);//将所有表添加到链表 rs.close(); 字符串 masterQuery = ""; for (int i = 0; i columnList = new LinkedList(); 对于 (int j = 1; j 0) for (int j = 0; j

【参考方案1】：

您可以阅读这篇关于检索 postgres 元数据的信息 article。

通常您必须深入了解 INFORMATION SCHEMA 或使用系统目录。

编辑 此外，将尽可能多的逻辑放入 SQL 中，以避免检索和处理您根本不需要的数据。

这是上述文章的复制/粘贴，其中列出了所有约束（您会在此处找到这两种方法）

SELECT c.conname AS constraint_name,
          CASE c.contype
            WHEN 'c' THEN 'CHECK'
            WHEN 'f' THEN 'FOREIGN KEY'
            WHEN 'p' THEN 'PRIMARY KEY'
            WHEN 'u' THEN 'UNIQUE'
          END AS "constraint_type",
          CASE WHEN c.condeferrable = 'f' THEN 0 ELSE 1 END AS is_deferrable,
          CASE WHEN c.condeferred = 'f' THEN 0 ELSE 1 END AS is_deferred,
          t.relname AS table_name,
          array_to_string(c.conkey, ' ') AS constraint_key,
          CASE confupdtype
            WHEN 'a' THEN 'NO ACTION'
            WHEN 'r' THEN 'RESTRICT'
            WHEN 'c' THEN 'CASCADE'
            WHEN 'n' THEN 'SET NULL'
            WHEN 'd' THEN 'SET DEFAULT'
          END AS on_update,
          CASE confdeltype
            WHEN 'a' THEN 'NO ACTION'
            WHEN 'r' THEN 'RESTRICT'
            WHEN 'c' THEN 'CASCADE'
            WHEN 'n' THEN 'SET NULL'
            WHEN 'd' THEN 'SET DEFAULT'
          END AS on_delete,
          CASE confmatchtype
            WHEN 'u' THEN 'UNSPECIFIED'
            WHEN 'f' THEN 'FULL'
            WHEN 'p' THEN 'PARTIAL'
          END AS match_type,
          t2.relname AS references_table,
          array_to_string(c.confkey, ' ') AS fk_constraint_key
     FROM pg_constraint c
LEFT JOIN pg_class t  ON c.conrelid  = t.oid
LEFT JOIN pg_class t2 ON c.confrelid = t2.oid
    WHERE t.relname = 'testconstraints2'
     AND c.conname = 'testconstraints_id_fk';

-- with INFORMATION_SCHEMA:

   SELECT tc.constraint_name,
          tc.constraint_type,
          tc.table_name,
          kcu.column_name,
      tc.is_deferrable,
          tc.initially_deferred,
          rc.match_option AS match_type,
          rc.update_rule AS on_update,
          rc.delete_rule AS on_delete,
          ccu.table_name AS references_table,
          ccu.column_name AS references_field
     FROM information_schema.table_constraints tc
LEFT JOIN information_schema.key_column_usage kcu
       ON tc.constraint_catalog = kcu.constraint_catalog
      AND tc.constraint_schema = kcu.constraint_schema
      AND tc.constraint_name = kcu.constraint_name
LEFT JOIN information_schema.referential_constraints rc
       ON tc.constraint_catalog = rc.constraint_catalog
      AND tc.constraint_schema = rc.constraint_schema
      AND tc.constraint_name = rc.constraint_name
LEFT JOIN information_schema.constraint_column_usage ccu
       ON rc.unique_constraint_catalog = ccu.constraint_catalog
      AND rc.unique_constraint_schema = ccu.constraint_schema
      AND rc.unique_constraint_name = ccu.constraint_name
    WHERE tc.table_name = 'testconstraints2'
      AND tc.constraint_name = 'testconstraints_id_fk';

【讨论】：

附加链接：postgresql.org/docs/9.0/static/catalog-pg-constraint.html

哇，真快。谢谢你。我会试一试。

【参考方案2】：

您可以在 DatabaseMetaData 中查询此类信息：

public static void main(String[] args) throws Exception 
    Connection connection = null;
    try 
        Class.forName(DRIVER);
        connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);

        DatabaseMetaData metadata = connection.getMetaData();
        ResultSet resultSet = metadata
            .getExportedKeys(null, null, TABLE);
        while (resultSet.next()) 
        String pkTableName = resultSet.getString("PKTABLE_NAME");
        String pkColName = resultSet.getString("PKCOLUMN_NAME");
        String fkTableName = resultSet.getString("FKTABLE_NAME");
        String fkColName = resultSet.getString("FKCOLUMN_NAME");
        
     catch (SQLException e) 
        e.printStackTrace();
     finally 
        connection.close();
    
    

见DatabaseMetaData