问题描述
修改,改变了code稍微基于下面的答案,但依然没有得到它的工作。我还添加了日志消息,告诉我,如果getCount将被返回> 0,这是,所以我supect财产以后可能是错的我的查询?或我使用了游标..
EDIT,Changed the code slightly based on answers below, but still haven't got it working. I also added a log message to tell me if getCount was returning > 0, and it was, so i supect somthing might be wrong with my query? or my use of the cursor..
我已经创建了一个表,我要检查其是否为空或不,如果它是空的,我想运行一些插入语句(存储在一个数组)。
I've created a table, and i want to check if its empty or not, if it's empty i want to run some insert statements (that are stored in an array).
下面是我的code,而我没有错误,当我拉.db文件出来,我可以看到,这是行不通的。你会如何处理这个问题?
Below is my code, while i have no errors, when i pull the .db file out i can see that it doesn't work. How would you approach this problem?
public void onCreate(SQLiteDatabase db) {
Log.i("DB onCreate", "Creating the database...");//log message
db.execSQL(createCATBUDTAB);
db.execSQL(createTWOWEETAB);
try{
Cursor cur = db.rawQuery("SELECT COUNT(*) FROM CAT_BUD_TAB", null);
if (cur.getCount() > 0){
Log.i("DB getCount", " getcount greater than 0");//log message
//do nothing everything's as it should be
}
else{//put in these insert statements contained in the array
Log.i("DB getCount", " getcount less than 0, should read array");//log message
for(int i=0; i<13; i++){
db.execSQL(catInsertArray[i]);
}
}
}catch(SQLiteException e){System.err.println("Exception @ rawQuery: " + e.getMessage());}
}
抱歉,如果这是一个pretty的愚蠢的问题或办法,我是新来的这一切。任何答案多少AP preciated!
Sorry if this is a pretty stupid question or approach, i'm new to all this. Any answers much appreciated!
推荐答案
查询 SELECT COUNT(*)
上现有的表应该的永远的返回null。如果没有行,在表中,则它应该返回一行包含零值。
The query SELECT COUNT(*)
on an existing table should never return null. If there are no rows in the table, it should return one row containing the value zero.
相反地,一排具有非零值表示它的的不的空
Conversely, a row with a non-zero value indicates that it's not empty.
在这两种情况下,一排应返回的,这意味着它将始终经过
In both cases, one row should be returned, meaning that it will always go through the
//do nothing everything's as it should be
部分。
要解决这个问题,留下您的查询的,是(你不想做选择列名
仅仅是因为这将是不必要的,可能是有点低效率)。把它作为 SELECT COUNT(*)
,它总是会返回一行,并使用以下code(只在我的脑海测试,所以要小心):
To fix it, leave your query as-is (you don't want to do select column_name
simply because that would be unnecessary and possibly a little inefficient). Leave it as select count(*)
, which will always return one row, and use the following code (tested only in my head so be careful):
Cursor cur = db.rawQuery("SELECT COUNT(*) FROM CAT_BUD_TAB", null);
if (cur != null) {
cur.moveToFirst(); // Always one row returned.
if (cur.getInt (0) == 0) { // Zero count means empty table.
for (int i = 0; i < 13; i++) {
db.execSQL (catInsertArray[i]);
}
}
}
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