如何检查我的 sqlite 表中是否有数据? [英] How can i check to see if my sqlite table has data in it?

问题描述

编辑，根据以下答案稍微更改了代码，但仍然无法正常工作.我还添加了一条日志消息，告诉我 getCount 是否返回 > 0，而且确实如此，所以我怀疑我的查询可能有问题?或者我对光标的使用..

我创建了一个表，我想检查它是否为空，如果它为空我想运行一些插入语句(存储在数组中).

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).

下面是我的代码，虽然我没有错误，但当我拉出 .db 文件时，我可以看到它不起作用.你会如何解决这个问题?

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());}
    }

对不起，如果这是一个非常愚蠢的问题或方法，我是这一切的新手.非常感谢任何答案！

Sorry if this is a pretty stupid question or approach, i'm new to all this. Any answers much appreciated!

推荐答案

对现有表的查询 SELECT COUNT(*) 应该从不返回 null.如果表中没有行，它应该返回包含值零的一行.

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，具有非零值的行表示它非空.

Conversely, a row with a non-zero value indicates that it's not empty.

在这两种情况下，都应该返回一行，这意味着它将始终通过

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.

要修复它，请保持查询原样(您不想执行 select column_name 仅仅因为那是不必要的，并且可能有点低效).将其保留为 select count(*)，它将始终返回一行，并使用以下代码(仅在我的脑海中测试过，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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