Android 使用 SQLiteDatabase 从多个表中查询 SQLite
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SQLite query from multiple tables using SQLiteDatabase
提问by user1049280
I have 2 tables in my database, for example: Table1: id (PK), data1and Table2: id (PK), id_table1 (FK), data2. How can I make a query like that:
我的数据库中有 2 个表，例如：Table1: id (PK), data1和Table2: id (PK), id_table1 (FK), data2. 我如何进行这样的查询：
SELECT * FROM Table1, Table2 WHERE Table1.id = Table2.id_table1
GROUP BY Table1.data1
I'm using SQLiteDatabaseand its query()method.
我正在使用SQLiteDatabase它的query()方法。
Cursor mCursor = db.query(true, new String[] {"Table1","Table2"},
new String[] {"Table1.id","data1", "Table2.id", "id_table1", "data2"},
"Table1.id=Table2.id_table1", null, "Table1.data1", null,null,null);
But there's a problem with the second arg - it's only possible to use String, not String[] (like new String[] {"Table1","Table2}). What should I do to make a query from multiple tables in that way?
但是第二个 arg 存在问题 - 只能使用 String，而不能使用 String[]（如new String[] {"Table1","Table2}）。我应该怎么做才能以这种方式从多个表中进行查询？
回答by Graham Borland
Try this:
尝试这个：
Cursor mCursor = db.rawQuery("SELECT * FROM Table1, Table2 " +
"WHERE Table1.id = Table2.id_table1 " +
"GROUP BY Table1.data1", null);
回答by Simon Dorociak
So when you need to JOINTables, you have to use rawQueryinstead of query.
So your statement
所以当你需要JOINTables 时，你必须使用rawQuery而不是query. 所以你的说法
String SELECT_QUERY = SELECT * FROM Table1 t1 INNER JOIN Table2 t2 ON t1.id = t2.id GROUP BY t1.data1;
I recommend to you use JOINbecause it more faster and safer then your approach. So then your rawQuerymethod can looks like this:
我建议您使用JOIN它，因为它比您的方法更快、更安全。那么你的rawQuery方法可以是这样的：
cursor = db.rawQuery(SELECT_QUERY, null);
Have look at rawQuery in SQLiteDatabase
Regards
问候
