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java – Return all columns of a SQLite table in Android

Posted by: admin April 23, 2020 Leave a comment

Questions:

The SQLite database table I’m using is subjected to adding columns whenever I need to. I don’t want to hard-code the columns at the risk of updating the database and forgetting to update the hard-coded values. How could I return all the names of the columns in a table? (Preferably in a String[])

How to&Answers:

Best if you use a SQLiteDatabase instance and use query method

SQLiteDatabase mDataBase;
(some code here...)
mDataBase = getReadableDatabase();
Cursor dbCursor = mDataBase.query(TABLE_NAME, null, null, null, null, null, null);
String[] columnNames = dbCursor.getColumnNames();

columnNames should have the column names

Answer:

You may not need a list of column names.

It seems that you want the list of column names so that you can build up a comma-separated list of columns to select. If this is the case, then where you would normally place the list of column names in your SELECT query, you could instead use an asterisk:

SELECT * FROM table WHERE ...

Or if the table is aliased:

SELECT t.* FROM table AS t ...

An asterisk means “all columns”.

EDIT: If you really do want a list of column names of a table, then you can use the following code:

Cursor c = db.rawQuery("SELECT * FROM table WHERE 0", null);
try {
    String[] columnNames = c.columnNames();
} finally {
    c.close();
}

Note that you must not modify the returned array of Strings in any way: https://code.google.com/p/android/issues/detail?id=3731

Answer:

It is also interesting to note that the query method accept null as input for the column parameters. If you input null, all the columns will be returned.

db.query("Table_name",null,COLUMN_ID + "=" + id,null,null,null,null);

Will return all columns of the line that has the specified id.

You can see the method definition here.