Develop Reference

Android SQLite: Doubts in Cursor

I am currently learning android SQLite database programming. While reading this tutorial from here. I came across a section of code,
getContact()
// Getting single contact
public Contact getContact(int id) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
KEY_NAME, KEY_PH_NO }, KEY_ID + "=?",
new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getString(2));
// return contact
return contact;
}
My Questions
Question 1
If this code returns the query ,
Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
KEY_NAME, KEY_PH_NO }, KEY_ID + "=?",
new String[] { String.valueOf(id) }, null, null, null, null);
Why do we move the cursor to the first row in this line ?
cursor.moveToFirst();
Question 2
What does this code do ?
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getString(2));
I read the official documentation but still could not understand. Can some one explain with a simple example ?

Question 1: Because Cursor is set before first row element initially.
Question 2: It gets Strings from row which is set as current in cursor object from columns (every row consists of columns) with numbers 0, 1 and 2. Then it uses them to create contact object.

sql exception,no such column exist(android)

I want to fetch record according to item_name..but it gives sql exception no such column: Roti exist.
query of my code is there
db.query(TABLE_1, new String[] { KEY_ITEM_CALORIES }, KEY_ITEM_NAME + "=" + item_name, null, null, null, null, null);
whats is the problem in this query?

you can make like that
Cursor mCursor=db.query(tablename, new String[] {"columnname1","columnname2"},"KEY_ITEM_NAME=?",new String[] { item_name }, null, null,null);

Try this
`Cursor cursor = db.rawQuery
("select * from Table_Name where Column_Name ='"+ value +"'", null)

Android programming sqlite database sorting query by String value to listview

I have a query that gets data from an sqlite database based on the Day value using a where clause, The data i'm getting is for 'Monday' this data is then populated into a listview. In addition to this i want to order the data by the time in ascending order to form a list with all events on monday from the earliest to latest Start times.
Query by day:
public Cursor getMonday () {
String Monday = "Monday";
return db.query(
DATABASE_TABLE,
new String[] { KEY_ID, KEY_LESSON, KEY_DAY, KEY_START, KEY_END, KEY_LOCATION},
KEY_DAY + "=?",
new String[] {Monday},
null, null, null);
}
I've tried:
public Cursor getMonday () {
String Monday = "Monday";
return db.query(DATABASE_TABLE,
new String[] {KEY_ID, KEY_LESSON, KEY_DAY, KEY_START,KEY_END, KEY_LOCATION},
KEY_DAY + "=?",
new String[] {Monday},
null, null, null,
KEY_START + " ASC");
}
This would usually work but i imagine that the WHERE clause and order by are not in the right order and i dont know how to make them work in unison. Could someone please advise? Thanks.
This is the error im getting:
01-28 14:24:02.738: E/AndroidRuntime(1672): FATAL EXCEPTION: main
01-28 14:24:02.738: E/AndroidRuntime(1672): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.unischeduler/com.example.unischeduler.ScheduleActivity}: java.lang.IllegalArgumentException: invalid LIMIT clauses:Start ASC

Your argument order is incorrect, try this:
public Cursor getMonday () {
String Monday = "Monday";
return db.query(DATABASE_TABLE,
new String[] {KEY_ID, KEY_LESSON, KEY_DAY, KEY_START,
KEY_END, KEY_LOCATION}, KEY_DAY + "=?",
new String[] {Monday}, null, null, KEY_START + " ASC", null);
}
EDIT Proposal to order by hh:mm format:
Take a look to SQLite Date and Time Functions and maybe you could try (I haven't tested it) something like this:
return db.query(DATABASE_TABLE,
new String[] {KEY_ID, KEY_LESSON, KEY_DAY, KEY_START,
KEY_END, KEY_LOCATION}, KEY_DAY + "=?",
new String[] {Monday}, null, null, "strftime('%H:%M', " + KEY_START + ")", null);

SQLite syntax error near "%"

I get this error
android.database.sqlite.SQLiteException: near "%": syntax error: , while compiling: SELECT _id, word, meaning FROM todo WHERE KEY_WORD = +%D9%84
for this
database.query(DATABASE_TABLE, new String[] {
KEY_ROWID, KEY_WORD, KEY_MEANING }, "KEY_WORD = " +word, null, null,
null, null,null);
when word is +%D9%84

You have to escape the SQL query. To do this, use the selectionArgs field (right after "KEY_WORD = " +word in your code). It will replace any ? in the selection field with its elements:
database.query(DATABASE_TABLE, new String[] {
KEY_ROWID, KEY_WORD, KEY_MEANING }, KEY_WORD + " = ?", new String[] { word },
null, null, null, null);
For more details, read this.

You have to quote the word with" characters. If you want to use wildcards, you have to use the like comparison operator instead of =.

Unable to fetch an sqlite record

I am using the following query to fetch a row with a particular mid.
Cursor mCursor = mDb.query(true, DATABASE_TABLE, new String[] { KEY_ROWID, "actionData", "mid" }, "mid" + "=" + mid, null, null, null, null, null);
I however get an sqlite exception when I try to do the same. Any ideas?
The exception is -
Error: android.database.sqlite.SQLiteException: no such column: qVEl3: , while compiling: SELECT DISTINCT _id, actionData, mid FROM notifs WHERE mid=qVEl3

You missed the quotations:
SELECT DISTINCT _id, actionData, mid FROM notifs WHERE mid='qVEl3'
So your Android code should be :
Cursor mCursor = mDb.query(true, DATABASE_TABLE, new String[]
{ KEY_ROWID, "actionData", "mid" },
"mid=?", new String[] {mid}, null, null, null, null);
(that will prevent SQL injection too)

You'll want to use query parameters to avoid issues with quotes:
Cursor mCursor = mDb.query(
true,
DATABASE_TABLE,
new String[] { KEY_ROWID, "actionData", "mid" },
"mid = ?", // the ? is a placeholder.
new String[] { mid }, // sqlite will put the value of mid into the placeholder above.
null,
null,
null,
null);