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I am trying to check if a sqlite database is empty using
public boolean chkDB(){
boolean chk = false;
Cursor mCursor = db.rawQuery("SELECT * FROM " + DATABASE_TABLE, null);
if (mCursor != null){
mCursor.moveToFirst();
if (mCursor.getInt(0) == 0){
chk = false;
}
}else{
chk = true;
}
return chk;
}
but every time i call that method i get null pointer exception
My Logcat shows this
06-28 22:35:19.519: E/AndroidRuntime(441): at com.android.id.DBAdapter.chkDB(DBAdapter.java:82)
06-28 22:58:06.269: E/AndroidRuntime(621): FATAL EXCEPTION: main
06-28 22:58:06.269: E/AndroidRuntime(621): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.id/com.android.id.MainActivity}: java.lang.NullPointerException
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.os.Handler.dispatchMessage(Handler.java:99)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.os.Looper.loop(Looper.java:123)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.main(ActivityThread.java:4627)
06-28 22:58:06.269: E/AndroidRuntime(621): at java.lang.reflect.Method.invokeNative(Native Method)
06-28 22:58:06.269: E/AndroidRuntime(621): at java.lang.reflect.Method.invoke(Method.java:521)
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
06-28 22:58:06.269: E/AndroidRuntime(621): at dalvik.system.NativeStart.main(Native Method)
06-28 22:58:06.269: E/AndroidRuntime(621): Caused by: java.lang.NullPointerException
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.id.DBAdapter.chkDB(DBAdapter.java:82)
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.id.MainActivity.enterDB(MainActivity.java:66)
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.id.MainActivity.onCreate(MainActivity.java:23)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
06-28 22:58:06.269: E/AndroidRuntime(621): ... 11 more
641
SELECT COUNT(DISTINCT `TABLE_NAME`) AS anyAliasName FROM `INFORMATION_SCHEMA`. `COLUMNS` WHERE `table_schema` = 'yourDatabaseName'; The above syntax returns 0 if the database has notable otherwise it returns the number of tables.
Show activity on this post. import MySQLdb db = MySQLdb. connect(passwd="moonpie", db="thangs") results = db. query("""SELECT * from mytable limit 1""") if not results: print "This table is empty!"
To determine whether an SQLite database file is empty, execute the following query: SELECT COUNT(*) FROM sqlite_schema; You will get the number of objects (tables, indices, views, triggers) in the database or 0 if the file is empty.
The IS NULL constraint can be used whenever the column is empty and the symbol ( ' ') is used when there is empty value. mysql> SELECT * FROM ColumnValueNullDemo WHERE ColumnName IS NULL OR ColumnName = ' '; After executing the above query, the output obtained is.
mCursor.moveToFirst() Returns a boolean of whether it successfully found an element or not. Use it to move to the first row in the cursor and at the same time check if a row actually exists.
Cursor mCursor = db.rawQuery("SELECT * FROM " + DATABASE_TABLE, null);
Boolean rowExists;
if (mCursor.moveToFirst())
{
// DO SOMETHING WITH CURSOR
rowExists = true;
} else
{
// I AM EMPTY
rowExists = false;
}
You are trying to access a row in the cursor regardless of whether one exists or not.
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