如何在sqlite的原始查询中使用交叉联接
我进行了谷歌搜索，发现我也可以在SQlite Android中进行Cross Join，我已经尝试过，但是结果为空。我的程序有问题吗？或实际上交叉联接不能应用于原始查询？谢谢您的帮助。
注意：在我使用交叉联接之前，我尝试发送一个表（以JSONArray形式），并且该表可以工作，所以我认为在我的代码中使用交叉联接时会发生这种情况。
这是我的程序：
private JSONArray getResults()
{
Context context = this;
String myPath = String.valueOf(context.getDatabasePath("ekantin1.db"));// Set path to your database
//String myTable = DatabaseHelper.ORDER_TABLE_NAME;//Set name of your table
SQLiteDatabase myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
//String searchQuery = "SELECT * FROM " + myTable;
Cursor cursor = myDataBase.rawQuery(" SELECT * FROM " + DatabaseHelper.ORDER_TABLE_NAME + " CROSS JOIN " + DatabaseHelper.LINEITEMS_TABLE_NAME, null );
JSONArray resultSet = new JSONArray();
cursor.moveToFirst();
while (cursor.isAfterLast() == false) {
int totalColumn = cursor.getColumnCount();
JSONObject rowObject = new JSONObject();
for( int i=0 ; i< totalColumn ; i++ )
{
if( cursor.getColumnName(i) != null )
{
try
{
if( cursor.getString(i) != null )
{
Log.d("TAG_NAME", cursor.getString(i) );
rowObject.put(cursor.getColumnName(i) , cursor.getString(i) );
}
else
{
rowObject.put( cursor.getColumnName(i) , "" );
}
}
catch( Exception e )
{
Log.d("TAG_NAME", e.getMessage() );
}
}
}
resultSet.put(rowObject);
cursor.moveToNext();
}
cursor.close();
Log.d("TAG_NAME", resultSet.toString() );
Intent pass_data = new Intent(this,BluetoothOut.class);
pass_data.putExtra("pindah",resultSet.toString());
startActivity(pass_data);
return resultSet;
}
}
这是我的数据库助手：
public class DatabaseHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME="ekantins.db";
//tabel order
public static final String ORDER_TABLE_NAME="tb_order";
public static final String COL_1="ORDERID";
public static final String COL_2="USERID";
public static final String COL_3="PASSWORD";
public static final String COL_4="MEJA";
public static final String COL_5="TOPUP";
public static final String COL_6="SALDO";
//tabel lineitems
public static final String LINEITEMS_TABLE_NAME="tb_lineitems";
public static final String COL1 = "FOODID";
public static final String COL2 = "PRICE";
public static final String COL3 = "NUM";
public static final String COL4 = "RES";
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE IF NOT EXISTS " + ORDER_TABLE_NAME + " (ORDERID INTEGER PRIMARY KEY AUTOINCREMENT,USERID TEXT ,PASSWORD TEXT, MEJA TEXT, TOPUP TEXT, SALDO TEXT)");
db.execSQL("CREATE TABLE IF NOT EXISTS " + LINEITEMS_TABLE_NAME + " (FOODID TEXT ,PRICE TEXT, NUM TEXT, RES TEXT, ORDERID_FK INTEGER)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + ORDER_TABLE_NAME ); //Drop older table if exists
db.execSQL("DROP TABLE IF EXISTS " + LINEITEMS_TABLE_NAME ); //Drop older table if exists
onCreate(db);
}
public void delete (String FOODID) {
SQLiteDatabase database = this.getWritableDatabase();
database.execSQL("DELETE FROM " + LINEITEMS_TABLE_NAME + " WHERE " + COL1 + "= '" + FOODID + "'");
//Close the database
database.close();
}
public String Sum() {
SQLiteDatabase db = this.getWritableDatabase();
String[] columns = new String[] {"SUM("+COL4+")" };
Cursor cursor = db.query(LINEITEMS_TABLE_NAME, columns,null,null,null,null,null);
String result = "";
int index_SUM = cursor.getColumnIndex("SUM("+COL4+")");
for (cursor.moveToFirst(); !(cursor.isAfterLast()); cursor.moveToNext()) {
result = result + cursor.getString(index_SUM) + "\n";
}
return result;
}
public String getTopup() {
SQLiteDatabase db = this.getWritableDatabase();
Cursor cr=db.rawQuery("SELECT "+COL_5+" FROM "+ORDER_TABLE_NAME,null);
String topup="";
for(cr.moveToFirst();!cr.isAfterLast();cr.moveToNext()){
topup=cr.getString(cr.getColumnIndex(COL_5));
}
cr.close();
return topup;
}
public String getSaldo() {
SQLiteDatabase db = this.getWritableDatabase();
Cursor cr=db.rawQuery("SELECT "+COL_6+" FROM "+ORDER_TABLE_NAME,null);
String saldo="";
for(cr.moveToFirst();!cr.isAfterLast();cr.moveToNext()){
saldo=cr.getString(cr.getColumnIndex(COL_6));
}
cr.close();
return saldo;
}
}
1 个答案:
答案 0 :(得分：0)
我的程序有问题吗？
快速浏览并不会出现。
还是实际上交叉联接不能应用于原始查询？
我不认为有任何此类限制。
我认为问题很简单，您在 tb_lineitems 表中没有行。因此，SELECT * FROM tb_order将返回行。但是，当您联接tb_lineitems表时，没有返回联接行。
例如使用（ 请注意在注释掉SQL时如何不插入line_items ）：-
DROP TABLE IF EXISTS tb_order;
CREATE TABLE IF NOT EXISTS tb_order (ORDERID INTEGER PRIMARY KEY AUTOINCREMENT,USERID TEXT ,PASSWORD TEXT, MEJA TEXT, TOPUP TEXT, SALDO TEXT);
DROP TABLE IF EXISTS tb_lineitems;
CREATE TABLE IF NOT EXISTS tb_lineitems (FOODID TEXT ,PRICE TEXT, NUM TEXT, RES TEXT, ORDERID_FK INTEGER);
INSERT INTO tb_order VALUES
(null,'Fred','password','meja001','topup001','saldo001'),
(null,'Mary','password','meja002','topup002','saldo002'),
(null,'Bert','password','meja003','topup003','saldo003');
/*
INSERT INTO tb_lineitems VALUES
('food001','10.30','1','res001',1),
('food002','11.30','1','res002',1),
('food002','11.30','1','res002',2)
;
*/
SELECT * FROM tb_order;
SELECT * FROM tb_lineitems;
SELECT * FROM tb_order
CROSS
JOIN tb_lineitems
;
产生以下3个输出：-
从插入物中删除3个tb_lineitems的注释，结果是：-
-
请注意，按照：-
，CROSS JOIN的结果与JOIN的结果不同
-
如果联接运算符是“ CROSS JOIN”，“ INNER JOIN”，“ JOIN”或逗号 （“，”）并且没有ON或USING子句，则联接的结果 只是左侧和右侧数据集的笛卡尔积。
- SQL As Understood By SQLite - SELECT - 1. Determination of input data (FROM clause processing).
评论：-
我已经检查了数据库，tb_line项目和tb_order不是 空的。
您检查了哪个数据库？您正在尝试通过仔细检查代码来使用2。
在数据库帮助器中，您已将数据库定义为 ekantins.db 。但是，您可以在getResults方法中打开一个名为 ekantin1.db 的数据库。
在下面的文本中，请注意以下代码：-
//String myPath = String.valueOf(context.getDatabasePath("ekantin1.db"));// Set path to your database
String myPath = String.valueOf(context.getDatabasePath("ekantins.db"));// Set path to your database
仅对1个数据库运行少量代码修改
- 添加到数据库助手中的两种方法来添加订单和订单项（不包括在内）
- 以下代码被用作活动（即您的代码+更多代码）
- 尝试启动另一项活动的评论已被删除
-
getResults方法被两次调用，即在有任何数据之前和之后
：-
public class MainActivity extends AppCompatActivity {
DatabaseHelper mDBHlpr;
Cursor cursor;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDBHlpr = new DatabaseHelper(this);
JSONArray r1 = getResults();
String sql = " SELECT * FROM " + DatabaseHelper.ORDER_TABLE_NAME + " CROSS JOIN " + DatabaseHelper.LINEITEMS_TABLE_NAME;
cursor = mDBHlpr.getWritableDatabase().rawQuery(sql, null );
DatabaseUtils.dumpCursor(cursor);
// Only add data once
if (DatabaseUtils.queryNumEntries(mDBHlpr.getWritableDatabase(),DatabaseHelper.ORDER_TABLE_NAME) < 1) {
mDBHlpr.addOrder("Fred", "password", "m001", "t001", "s001");
mDBHlpr.addOrder("Mary", "password", "m001", "t001", "s001");
mDBHlpr.addOrder("Bert", "password", "m001", "t001", "s001");
cursor = mDBHlpr.getWritableDatabase().rawQuery(sql, null);
DatabaseUtils.dumpCursor(cursor);
mDBHlpr.addLineItem("F001", "10.30", "1", "1", 1);
mDBHlpr.addLineItem("F002", "11.30", "2", "2", 1);
mDBHlpr.addLineItem("F003", "12.30", "3", "3", 2);
cursor = mDBHlpr.getWritableDatabase().rawQuery(sql, null);
DatabaseUtils.dumpCursor(cursor);
}
JSONArray r2 = getResults();
}
private JSONArray getResults()
{
Context context = this;
//String myPath = String.valueOf(context.getDatabasePath("ekantin1.db"));// Set path to your database
String myPath = String.valueOf(context.getDatabasePath("ekantins.db"));// Set path to your database
String myTable = DatabaseHelper.ORDER_TABLE_NAME;//Set name of your table
SQLiteDatabase myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
//SQLiteDatabase myDataBase = mDBHlpr.getWritableDatabase();
//String searchQuery = "SELECT * FROM " + myTable;
Cursor cursor = myDataBase.rawQuery(" SELECT * FROM " + DatabaseHelper.ORDER_TABLE_NAME + " CROSS JOIN " + DatabaseHelper.LINEITEMS_TABLE_NAME, null );
JSONArray resultSet = new JSONArray();
cursor.moveToFirst();
while (cursor.isAfterLast() == false) {
int totalColumn = cursor.getColumnCount();
JSONObject rowObject = new JSONObject();
for( int i=0 ; i< totalColumn ; i++ )
{
if( cursor.getColumnName(i) != null )
{
try
{
if( cursor.getString(i) != null )
{
Log.d("TAG_NAME", cursor.getString(i) );
rowObject.put(cursor.getColumnName(i) , cursor.getString(i) );
}
else
{
rowObject.put( cursor.getColumnName(i) , "" );
}
}
catch( Exception e )
{
Log.d("TAG_NAME", e.getMessage() );
}
}
}
resultSet.put(rowObject);
cursor.moveToNext();
}
cursor.close();
Log.d("TAG_NAME", resultSet.toString() );
/*
Intent pass_data = new Intent(this,BluetoothOut.class);
pass_data.putExtra("pindah",resultSet.toString());
startActivity(pass_data);
*/
return resultSet;
}
}
结果是：-
08-04 07:05:36.895 1494-1494/pra.playrawaudio D/TAG_NAME: []
08-04 07:05:36.895 1494-1494/pra.playrawaudio I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@5343e554
<<<<<
08-04 07:05:36.907 1494-1494/pra.playrawaudio I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@53441ce0
<<<<<
08-04 07:05:36.915 1494-1494/pra.playrawaudio I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@53437acc
0 {
ORDERID=1
USERID=Fred
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F001
PRICE=10.30
NUM=1
RES=1
ORDERID_FK=1
}
1 {
ORDERID=1
USERID=Fred
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F002
PRICE=11.30
NUM=2
RES=2
ORDERID_FK=1
}
2 {
ORDERID=1
USERID=Fred
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F003
PRICE=12.30
NUM=3
RES=3
ORDERID_FK=2
}
3 {
ORDERID=2
USERID=Mary
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F001
PRICE=10.30
NUM=1
RES=1
ORDERID_FK=1
}
4 {
ORDERID=2
USERID=Mary
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F002
PRICE=11.30
NUM=2
RES=2
ORDERID_FK=1
}
5 {
ORDERID=2
USERID=Mary
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F003
PRICE=12.30
NUM=3
RES=3
ORDERID_FK=2
}
6 {
ORDERID=3
USERID=Bert
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F001
PRICE=10.30
NUM=1
RES=1
ORDERID_FK=1
}
7 {
ORDERID=3
USERID=Bert
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F002
PRICE=11.30
NUM=2
RES=2
ORDERID_FK=1
}
8 {
ORDERID=3
USERID=Bert
PASSWORD=password
MEJA=m001
TOPUP=t001
SALDO=s001
FOODID=F003
PRICE=12.30
NUM=3
RES=3
ORDERID_FK=2
}
<<<<<
08-04 07:05:36.919 1494-1494/pra.playrawaudio D/TAG_NAME: 1
Fred
password
m001
t001
s001
F001
10.30
1
1
1
08-04 07:05:36.923 1494-1494/pra.playrawaudio D/TAG_NAME: 1
Fred
password
m001
t001
s001
F002
11.30
2
2
1
1
Fred
password
m001
t001
s001
F003
12.30
3
3
2
2
Mary
password
m001
t001
s001
F001
10.30
1
1
1
2
Mary
password
m001
t001
s001
F002
11.30
2
2
1
2
Mary
password
m001
t001
s001
F003
12.30
3
3
2
3
Bert
password
m001
t001
s001
F001
10.30
1
1
1
3
Bert
password
m001
t001
s001
F002
11.30
2
2
1
3
Bert
password
m001
t001
s001
F003
12.30
3
3
2
08-04 07:05:36.927 1494-1494/pra.playrawaudio D/TAG_NAME: [{"PRICE":"10.30","RES":"1","ORDERID":"1","SALDO":"s001","MEJA":"m001","ORDERID_FK":"1","PASSWORD":"password","NUM":"1","TOPUP":"t001","FOODID":"F001","USERID":"Fred"},{"PRICE":"11.30","RES":"2","ORDERID":"1","SALDO":"s001","MEJA":"m001","ORDERID_FK":"1","PASSWORD":"password","NUM":"2","TOPUP":"t001","FOODID":"F002","USERID":"Fred"},{"PRICE":"12.30","RES":"3","ORDERID":"1","SALDO":"s001","MEJA":"m001","ORDERID_FK":"2","PASSWORD":"password","NUM":"3","TOPUP":"t001","FOODID":"F003","USERID":"Fred"},{"PRICE":"10.30","RES":"1","ORDERID":"2","SALDO":"s001","MEJA":"m001","ORDERID_FK":"1","PASSWORD":"password","NUM":"1","TOPUP":"t001","FOODID":"F001","USERID":"Mary"},{"PRICE":"11.30","RES":"2","ORDERID":"2","SALDO":"s001","MEJA":"m001","ORDERID_FK":"1","PASSWORD":"password","NUM":"2","TOPUP":"t001","FOODID":"F002","USERID":"Mary"},{"PRICE":"12.30","RES":"3","ORDERID":"2","SALDO":"s001","MEJA":"m001","ORDERID_FK":"2","PASSWORD":"password","NUM":"3","TOPUP":"t001","FOODID":"F003","USERID":"Mary"},{"PRICE":"10.30","RES":"1","ORDERID":"3","SALDO":"s001","MEJA":"m001","ORDERID_FK":"1","PASSWORD":"password","NUM":"1","TOPUP":"t001","FOODID":"F001","USERID":"Bert"},{"PRICE":"11.30","RES":"2","ORDERID":"3","SALDO":"s001","MEJA":"m001","ORDERID_FK":"1","PASSWORD":"password","NUM":"2","TOPUP":"t001","FOODID":"F002","USERID":"Bert"},{"PRICE":"12.30","RES":"3","ORDERID":"3","SALDO":"s001","MEJA":"m001","ORDERID_FK":"2","PASSWORD":"password","NUM":"3","TOPUP":"t001","FOODID":"F003","USERID":"Bert"}]
08-04 07:05:36.951 1494-1494/pra.playrawaudio I/dalvikvm: Could not find method android.view.ViewGroup$MarginLayoutParams.getLayoutDirection, referenced from method android.support.v4.view.MarginLayoutParamsCompat.getLayoutDirection
结果表明，所提供的代码或查询都没有问题。即当数据存在时返回结果
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