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I'm writing code on android. I try to write a code which take data from one column and add to another column's string, do this for all database.

Like this:

Before:

 A column | B column 
 string 1 string 2

After:

A column | B column 
 string 1 string 2+string 1

I'll try get strings from columns and update column but i can't do.

Database.KEY_COLUMN1 and Database.KEY_COLUMN2 are name of columns(string type)

SQLiteDatabase mydatabase = dbHelper.getMydatabase();
String query = new String( "select "+Database.KEY_COLUMN1+",
"+Database.KEY_COLUMN2'+ " from "+ Database.TABLE_NAME );
cursor = mydatabase.rawQuery(query,null);
while(cursor.moveToNext()) 
 String column1 = cursor.getString(cursor.getColumnIndex(Database.KEY_COLUMN1));
 String column2 = cursor.getString(cursor.getColumnIndex(Database.KEY_COLUMN2));
 column2=column1+colum2;
 mydatabase.execSQL("UPDATE "+Database.DATABASE_TABLE+" SET "
 + Database.KEY_COLUMN2+ " = "
 +Datababese.KEY_COLUMN1+ " + " + Database.KEY_COLUMN2
 +" WHERE "+Database.KEY_COLUMN2 + " = " +cursor.getColumnIndex(Database.KEY_COLUMN2)); 

cursor.close();

I updated exceSQL but it didn't write anyting to databese.

The problem with your UPDATE statement is that an UPDATE without a WHERE clause updates all rows of the table, so you end up with the same values in all rows.

If you wanted to update rows one by one, you would have to read the ID of the each row, and use that to filter the UPDATE, like this:

UPDATE MyTable SET BColumn = 'newValue' WHERE ID = 123

Anyway, you can simply execute a single command that does the string concatenation individually for each row:

UPDATE MyTable SET ArrayColumn = Column1 + Column2

or in Java:

db.execSQL("UPDATE " + Database.DATABASE_TABLE +
 " SET " + Database.KEY_ARRAY + " = " +
 Database.KEY_COLUMN1 + " + " + Database.KEY_COLUMN2);