Question

所以我一直在使用Android上的SQLite进行摔跤并解决了一些问题。问题包括here和here。

我现在想为给定的状态选择DISTINCT区域。我的第一个RecyclerView屏幕使用以下代码显示状态。

public Cursor getStateData() {
    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    String [] sqlSelect = {"0 _id", "state" };
    String sqlTables = "Reefs";
    qb.setTables(sqlTables);
    qb.setDistinct(true);
    Cursor c = qb.query(db, sqlSelect, null, null, null, null, null);
    c.moveToFirst();
    return c;
}

现在为每个州获取DISTINCT区域，我使用以下代码：

public Cursor getRegionData(String whichState) {
    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    String [] sqlSelect = {"0 _id", "region" };
    String theState = whichState;
    String sqlTables = "Reefs";
    qb.setTables(sqlTables);
    qb.setDistinct(true);
    Cursor c = qb.query(db, sqlSelect, theState , null , null, null, null);
    //  (table, columms to return,  colums for the where clause,  values for the where clause, null, null, null)
    c.moveToFirst();
    return c;
}

它不起作用并给我这个错误信息：

Caused by: android.database.sqlite.SQLiteException: no such column: Tasmania (code 1): , while compiling: SELECT DISTINCT 0 _id, region FROM Reefs WHERE (Tasmania)

我从列表中选择了塔斯马尼亚，因此塔斯马尼亚作为字符串参数 whichState 传入。

因此，如果我用纯粹的SQL术语来描述问题，那就是这样的：

SELECT
  region  //column in my table called region
FROM
  Reefs  // table in my database
WHERE
  state = [the state selected]  //column in my table called **state** which I pass in with the varible **whichState**

我做错了什么？

Answer 1

您传递的是值，而不是WHERE条款，请参阅documentation。

要更正它，请传递WHERE子句和参数：

public Cursor getRegionData(String whichState) {
    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    String [] sqlSelect = {"0 _id", "region" };
    String [] theState = { whichState };
    String sqlTables = "Reefs";
    qb.setTables(sqlTables);
    qb.setDistinct(true);
    Cursor c = qb.query(db, sqlSelect, "state=?", theState, null, null, null);
    c.moveToFirst();
    return c;
}

Answer 2

323go完美地挑选了它。这是我的完整代码，因为它可以帮助其他人解决同样的问题。

有趣的是，我将最后一个方法 getAreaData 整理得很好而且略有不同很高兴能正确使用该代码，因为我是sql的新手。

public Cursor getStateData() {
    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    String [] sqlSelect = {"0 _id", "state" };
    String sqlTables = "Reefs";
    qb.setTables(sqlTables);
    qb.setDistinct(true);
    Cursor c = qb.query(db, sqlSelect, null, null, null, null, null);
    c.moveToFirst();
    return c;
}

public Cursor getRegionData(String whichState) {
    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    String [] sqlSelect = {"0 _id", "region" };
    String [] theState = { whichState };
    String sqlTables = "Reefs";
    qb.setTables(sqlTables);
    qb.setDistinct(true);
    Cursor c = qb.query(db, sqlSelect, "state=?" , theState, null, null, null);
    //  (table, columms to return,  colums for the where clause,  values for the where clause, null, null, null)

    c.moveToFirst();
    return c;
}

public Cursor getAreaData(String whichState, String whichRegion) {
    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    String [] sqlSelect = {"0 _id", "state", "region", "area", "latitude", "longitude"};
    String sqlFilter = "state= '"+whichState+"' AND region= '"+whichRegion+"'";
    String [] sqlValues = {""};
    String sqlTables = "Reefs";
    qb.setTables(sqlTables);
    qb.setDistinct(true);
    Cursor c = qb.query(db, sqlSelect, sqlFilter, null, null, null, null);
    c.moveToFirst();
    return c;
}

selectionArgs错误表示列不存在

2 个答案: