java - 为什么 JDBC 驱动程序会在 Oracle 数据库中填充一些空白字符而不是查询字段？

Question

因此，这是在 Oracle 10g/UTF-8 数据库中创建表的代码:

CREATE TABLE TEST_SEMANTIC
(
SEMANTIC_COLBYTE char(2 byte) ,
SEMANTIC_COLCHAR char(2 char)
);

意思是，我对字节和字符这两列使用了两种不同类型的语义。

然后我在数据库中插入这些相应的数据:

insert into test_semantic(SEMANTIC_COLBYTE,SEMANTIC_COLCHAR)
values('é','é');

所以当我在 java 程序中使用 JDBC 驱动程序查询数据库并显示结果时，我希望得到这样的输出:

Byte>é<
Char>é<

而我明白了:

Byte>é<
Char>é      <

当我这样查询数据库时:

select dump(semantic_colbyte,16),dump(semantic_colchar,16) from test_semantic;

我明白了:

Typ=96 Len=2: c3,a9 Typ=96 Len=3: c3,a9,20

这是Java代码:

public static void main(String[] args){
        Connection con = null;
        try {
            Class.forName("oracle.jdbc.driver.OracleDriver");

        } catch (java.lang.ClassNotFoundException e) {
            System.err.print("ClassNotFoundException:");
            System.err.println(e.getMessage());
        }

        try {
            Properties props = new Properties();
            props.put("user", "XXX");
            props.put("password", "XXX");

            con = DriverManager.getConnection("jdbc:oracle:thin:@xxx:1521:xxx", props);
            Statement stmt = (Statement) con.createStatement();
            stmt.execute("SELECT SEMANTIC_COLBYTE,SEMANTIC_COLCHAR FROM TEST_SEMANTIC"); 
            ResultSet result = stmt.getResultSet();
            result.next();
            String output_byte = result.getString(1);
            String output_char = result.getString(2);

        System.out.println("Byte>"+output_byte+"<");                
        System.out.println("Char>"+output_char+"<");

        } catch (SQLException ex) {
            System.err.println("SQLException: " + ex.getMessage());
        }
    }

Answer 1

CHAR Datatype :

The CHAR datatype specifies a fixed-length character string. Oracle ensures that all values stored in a CHAR column have the length specified by size. If you insert a value that is shorter than the column length, then Oracle blank-pads the value to column length.