Question

我是Android开发和SQLite数据库的新手，所以请关注我（也是我在这个网站上的第一个问题，希望它没关系）。

所以，我的数据库由三个表组成：

表records
表locations
表tags

这就是我创建表格的方式：

private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "recordsDatabase";

//Common columns
public static final String ID = "id";
public static final String NAME_COLUMN = "name";

//Tables
public static final String TABLE_RECORDS = "records";
public static final String TABLE_LOCATIONS = "locations";
public static final String TABLE_TAGS = "tags";

//Records table
public static final String KEY_CREATED_AT = "date";
public static final String STARTINGHOUR = "startingHour";
public static final String FINISHINGHOUR = "finishingHour";
public static final String COMMENTS = "comments";
public static final String LOCATIONS_ID = "locationsID";
public static final String TAGS_ID = "tagsID";

//Create table statements
public static final String CREATE_TABLE_RECORDS = "CREATE TABLE "
    + TABLE_RECORDS + "(" + ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
    + NAME_COLUMN + " TEXT,"
    + KEY_CREATED_AT + " DATETIME,"
    + STARTINGHOUR + " TEXT,"
    + FINISHINGHOUR + " TEXT,"
    + COMMENTS + " TEXT,"
    + LOCATIONS_ID + " INTEGER, "
    + TAGS_ID + " INTEGER, "
    + "FOREIGN KEY(" + LOCATIONS_ID + ") REFERENCES " + TABLE_LOCATIONS + "(id),"
    + "FOREIGN KEY(" + TAGS_ID + ") REFERENCES " + TABLE_TAGS + "(id))";

public static final String CREATE_TABLE_LOCATIONS = "CREATE TABLE "
    + TABLE_LOCATIONS + "(" + ID + " INTEGER PRIMARY KEY,"
    + NAME_COLUMN + ")";

public static final String CREATE_TABLE_TAGS = "CREATE TABLE "
    + TABLE_TAGS + "(" + ID + " INTEGER PRIMARY KEY,"
    + NAME_COLUMN + ")";

稍后，在onOpen方法中，我创建了以下PRAGMA语句：

if(!db.isReadOnly()) db.execSQL("PRAGMA foreign_keys=ON;");

如您所见，我使用外键在这些表之间建立关系。正如我所提到的，我对SQLite数据库来说是全新的，所以这里也可能存在问题，但我没有收到任何相关的失败。

但是，我被告知以下错误：

AndroidRuntime: FATAL EXCEPTION: AsyncTask #1 ... java.lang.RuntimeException: An error occured while executing doInBackground()
...
Caused by: android.database.sqlite.SQLiteException: near ".": syntax error (code 1): , while compiling: SELECT records.id, records.name ,date, startingHour, finishingHour, comments, locationsID, tagsID locations.name, tags.name FROM records records, locations locations, tags tags WHERE records.locationsID = locations.id AND tagsID = tags.id

指向以下代码行：

public static final String RECORDS_ID_WITH_PREFIX = "rec.id";
public static final String RECORDS_NAME_WITH_PREFIX = "rec.name";
public static final String LOCATIONS_NAME_WITH_PREFIX = "loc.name";
public static final String TAGS_NAME_WITH_PREFIX = "tg.name";
private static final String WHERE_ID_EQUALS = DatabaseHelper.ID + " =?";

//...some blocks of code in between...\\

String query = "SELECT " + RECORDS_ID_WITH_PREFIX + ", "       
    + RECORDS_NAME_WITH_PREFIX + " ,"
    + DatabaseHelper.KEY_CREATED_AT + ", "
    + DatabaseHelper.STARTINGHOUR + ", "
    + DatabaseHelper.FINISHINGHOUR + ", "
    + DatabaseHelper.COMMENTS + ", "
    + DatabaseHelper.LOCATIONS_ID + ", "
    + DatabaseHelper.TAGS_ID + " "+ LOCATIONS_NAME_WITH_PREFIX + ", " + TAGS_NAME_WITH_PREFIX + " FROM "
    + DatabaseHelper.TABLE_RECORDS + " rec, " + DatabaseHelper.TABLE_LOCATIONS + " loc, " + DatabaseHelper.TABLE_TAGS + " tg "
    + " WHERE rec." + DatabaseHelper.LOCATIONS_ID + " = loc." + DatabaseHelper.ID + " AND "
    + DatabaseHelper.TAGS_ID + " = tg." + DatabaseHelper.ID;

我之所以提出这个问题的原因是SELECT查询应遵循以下语法：

SELECT [columns] FROM [table name] WHERE [conditions];

但如果我看一下我的语法，我认为没有错。现在我使用RECORDS_ID_WITH_PREFIX，RECORDS_NAME_WITH_PREFIX，LOCATIONS_NAME_WITH_PREFIX和LOCATIONS_NAME_WITH_PREFIX的原因是为了避免混淆，因为id和name列在所有表中都很常见。有人愿意看一看，帮助我理解我做错了吗？

另外，如果您认为我的问题有问题，请告诉我，以便将来不会再犯同样的错误。

Answer 1

+ DatabaseHelper.TAGS_ID + " "+ LOCATIONS_NAME_WITH_PREFIX + ", " +
                           ^^^

缺少逗号

由SQLiteException引起的RuntimeException，语法错误

1 个答案: