JDBC SQLite尝试获取可空列

问题描述

我正在尝试从Java中的SQLite Database检索所有可为空的列.

I am trying to retrieve all nullable columns from an SQLite Database in Java.

我不知道为什么当有两列具有not null属性的列时，JDBC为什么只返回主键为Not NULL.

I don't know why JDBC is returning that only the primary key is Not NULL when there are two columns with not nullproperty.

CREATE TABLE `univDB` (
        `x` INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
        `FirstColumn`   TEXT NOT NULL,
        `SecondColumn`  TEXT
    );

以及当我运行以下代码时:

and when I run the following code:

    ResultSet rs = stmt.executeQuery("SELECT * FROM "+table);

    for (int i=1; i<= rs.getMetaData().getColumnCount(); i++) {
            System.out.println("NULLABLE column "+i+" "+rs.getMetaData().isNullable(i));
            if (ResultSetMetaData.columnNoNulls == rs.getMetaData().isNullable(i)) {
                System.out.println("Column Not Null "+rs.getMetaData().getColumnName(i));
            }
     }

我知道x是DB的唯一不可为空的列，但也应该有FirstColumn.

I get that x is the only non-nullable column of the DB but there should be FirstColumn too.

推荐答案

我在sqlite版本sqlite-jdbc-3.8.11.2

I had the same issue with sqlite version sqlite-jdbc-3.8.11.2

您可以改用此方法(来源:文档):

You can try this instead (source: Documentation):

try {
    DatabaseMetaData meta = dbConn.getMetaData();
    ResultSet rs_columns = meta.getColumns(null, null, table, null);
    while(rs_columns.next()) {
        String columnName = rs_columns.getString(4); // Columnname
        String nullable = rs_columns.getString(18); // Nullable returns smth like "NO" or "YES"
        System.out.println("clmn: " + columnName);
        System.out.println("IsNullable: " + nullable);
    }

    // OR directly
    String columnName = "A_CLMM_NAME";
    ResultSet rs_column = meta.getColumns(null, null, table, columnName);
    if(rs_column.next()) {
        String nullable = rs_column.getString(18); // Nullable
    }
} catch (Exception e) {
    e.printStackTrace();
}

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