Question

我知道如何使用.getTables()来获取TABLE和ALIAS条目。

final ResultSet rs = dmd.getTables(null, "MySchema", "%", new String[]{"TABLE","ALIAS"});

我需要确定哪个ALIAS与哪个TABLE名称相关？

我特别需要能够在Oracle，SQL Server和DB2上执行此操作。

鉴于我有一个表格T00001，其别名为MyTable，如何使用DatabaseMetaData来电中的Connection.getMetaData()来匹配这两个？

Answer 1

在查看JDBC API和oracle.jdbc.OracleDatabaseMetaData之后，我非常确定在使用库存Oracle JDBC驱动程序时无法通过DatabaseMetaData直接检索此信息。 DB2或SQL Server可能存在特定于驱动程序的方法，因为我没有彻底检查它们。作为作弊，您可以从DatabaseMetaData对象getConnection()运行特定于数据库的查询以检索所需的信息，如下所示：

public class TableAliasMapperJdbc {
    public Map<String, List<String>> mapTableAliases(String url, String user, String password, String sql) throws SQLException {
        try (
            Connection conn = DriverManager.getConnection(url, user, password);
            // we use conn.getMetaData().getConnection() instead of conn here only to fit within the parameters of the question
            PreparedStatement stmt = conn.getMetaData().getConnection().prepareStatement(sql);
            ResultSet rs = stmt.executeQuery();
        ) {
            // this may not do what you want if you have synonyms of synonyms
            Map<String, List<String>> tableAliases = new HashMap<>();
            while (rs.next()) {
                String table = rs.getString(1);
                String alias = rs.getString(2);
                List<String> aliases = tableAliases.get(table);
                if (aliases == null) {
                    tableAliases.put(table, aliases = new ArrayList<>(2));
                }
                aliases.add(alias);
            }
            return tableAliases;
        }
    }

    public void print(String dbName, Map<String, List<String>> tableAliases) {
        System.out.format("\nThe following are the table aliases for %s:\n", dbName);
        for (Map.Entry<String, List<String>> entry : tableAliases.entrySet()) {
            System.out.format("The alias(es) for %s are: %s.\n", entry.getKey(), String.join(", ", entry.getValue()));
        }
    }

    public static void main(String[] args) throws SQLException {
        TableAliasMapperJdbc mapper = new TableAliasMapperJdbc();
        mapper.print("Oracle",
            mapper.mapTableAliases(
                "jdbc:oracle:thin:@localhost:1521:xe",
                "scott",
                "tiger",
                "SELECT table_name, synonym_name FROM user_synonyms")); // or maybe all_synonyms

        mapper.print("DB2",
            mapper.mapTableAliases(
                "jdbc:db2://localhost:50000/SAMPLE",
                "db2admin",
                "db2admin",
                "SELECT base_tabname, tabname FROM syscat.tables WHERE type = 'A' AND owner = 'DB2ADMIN'"));

        mapper.print("SQL Server",
            mapper.mapTableAliases(
                "jdbc:sqlserver://localhost:1433",
                "sa",
                "Password123",
                "SELECT PARSENAME(base_object_name,1), name FROM sys.synonyms"));
    }
}

使用JDK 1.8.0_45，Oracle XE 11.2.0.2.0及其捆绑的JDBC驱动程序DB2 Express-C 10050500及其捆绑的JDBC驱动程序以及带有Microsoft JDBC Driver 4.1的SQL Server 2014 Express 12.0.2000.8成功测试了代码.5605.100。

<子> 基于http://sqlblog.com/blogs/john_paul_cook/archive/2010/08/24/script-to-list-synonym-contents.aspx的SQL Server查询。

从DatabaseMetaData在运行时匹配表名和别名？

1 个答案: