Android SQLite: order by many columns - android

TABLE_NAME (COL1, COL2, COL3, COL4);
Cursor cur = db.query(TABLE_NAME, null, null, null, null, null, COL1);
This way we get the entries ordered by COL1 values. If some of them has the same COL1 value SQLite uses the same order as when they were stored by the previous insertions.
Is it possible to define many degrees of sorting? For example, if two or more entries has the same COL1 value then the one with the smaller COL2 value will go first and so on.
Android site says that we can specify only a String (column) for the sorting.
query(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy)
If I use a
db.rawQuery("sql code")
the string of sql code will be compiled at runtime so the program will be slower. I would like to avoid that if not necessary. Are there any other ways?

With String orderBy you could specify multiple columns as this:
String order = COL1 + ", " +COL2 + ", " + COL3;
Cursor cur = db.query(TABLE_NAME, null, null, null, null, null, order);

Related

Passing parameters into SQLite querys [duplicate]

I am using the query method of SQLiteDatabase. How do I use the query method?
I tried this:
Cursor cursor = sqLiteDatabase.query(
tableName, tableColumns, whereClause, whereArgs, groupBy, having, orderBy);
tableColumns - columns parameter is constructed as follows.
String[] columns = new String[]{KEY_ID, KEY_CONTENT};
If we need to get all the fields, how should the column parameter to be constructed. Do we need to include all the Field Names in String array?
How do I properly use the query method?
tableColumns
null for all columns as in SELECT * FROM ...
new String[] { "column1", "column2", ... } for specific columns as in SELECT column1, column2 FROM ... - you can also put complex expressions here:
new String[] { "(SELECT max(column1) FROM table1) AS max" } would give you a column named max holding the max value of column1
whereClause
the part you put after WHERE without that keyword, e.g. "column1 > 5"
should include ? for things that are dynamic, e.g. "column1=?" -> see whereArgs
whereArgs
specify the content that fills each ? in whereClause in the order they appear
the others
just like whereClause the statement after the keyword or null if you don't use it.
Example
String[] tableColumns = new String[] {
"column1",
"(SELECT max(column1) FROM table2) AS max"
};
String whereClause = "column1 = ? OR column1 = ?";
String[] whereArgs = new String[] {
"value1",
"value2"
};
String orderBy = "column1";
Cursor c = sqLiteDatabase.query("table1", tableColumns, whereClause, whereArgs,
null, null, orderBy);
// since we have a named column we can do
int idx = c.getColumnIndex("max");
is equivalent to the following raw query
String queryString =
"SELECT column1, (SELECT max(column1) FROM table1) AS max FROM table1 " +
"WHERE column1 = ? OR column1 = ? ORDER BY column1";
sqLiteDatabase.rawQuery(queryString, whereArgs);
By using the Where/Bind -Args version you get automatically escaped values and you don't have to worry if input-data contains '.
Unsafe: String whereClause = "column1='" + value + "'";
Safe: String whereClause = "column1=?";
because if value contains a ' your statement either breaks and you get exceptions or does unintended things, for example value = "XYZ'; DROP TABLE table1;--" might even drop your table since the statement would become two statements and a comment:
SELECT * FROM table1 where column1='XYZ'; DROP TABLE table1;--'
using the args version XYZ'; DROP TABLE table1;-- would be escaped to 'XYZ''; DROP TABLE table1;--' and would only be treated as a value. Even if the ' is not intended to do bad things it is still quite common that people have it in their names or use it in texts, filenames, passwords etc. So always use the args version. (It is okay to build int and other primitives directly into whereClause though)
This is a more general answer meant to be a quick reference for future viewers.
Example
SQLiteDatabase db = helper.getReadableDatabase();
String table = "table2";
String[] columns = {"column1", "column3"};
String selection = "column3 =?";
String[] selectionArgs = {"apple"};
String groupBy = null;
String having = null;
String orderBy = "column3 DESC";
String limit = "10";
Cursor cursor = db.query(table, columns, selection, selectionArgs, groupBy, having, orderBy, limit);
Explanation from the documentation
table String: The table name to compile the query against.
columns String: A list of which columns to return. Passing null will return all columns, which is discouraged to prevent reading data
from storage that isn't going to be used.
selection String: A filter declaring which rows to return, formatted as an SQL WHERE clause (excluding the WHERE itself). Passing
null will return all rows for the given table.
selectionArgs String: You may include ?s in selection, which will be replaced by the values from selectionArgs, in order that they
appear in the selection. The values will be bound as Strings.
groupBy String: A filter declaring how to group rows, formatted as an SQL GROUP BY clause (excluding the GROUP BY itself). Passing null
will cause the rows to not be grouped.
having String: A filter declare which row groups to include in the cursor, if row grouping is being used, formatted as an SQL HAVING
clause (excluding the HAVING itself). Passing null will cause all row
groups to be included, and is required when row grouping is not being
used.
orderBy String: How to order the rows, formatted as an SQL ORDER BY clause (excluding the ORDER BY itself). Passing null will use the
default sort order, which may be unordered.
limit String: Limits the number of rows returned by the query, formatted as LIMIT clause. Passing null denotes no LIMIT clause.
Where clause and args work together to form the WHERE statement of the SQL query. So say you looking to express
WHERE Column1 = 'value1' AND Column2 = 'value2'
Then your whereClause and whereArgs will be as follows
String whereClause = "Column1 =? AND Column2 =?";
String[] whereArgs = new String[]{"value1", "value2"};
If you want to select all table columns, i believe a null string passed to tableColumns will suffice.
if your SQL query is like this
SELECT col-1, col-2 FROM tableName WHERE col-1=apple,col-2=mango
GROUPBY col-3 HAVING Count(col-4) > 5 ORDERBY col-2 DESC LIMIT 15;
Then for query() method, we can do as:-
String table = "tableName";
String[] columns = {"col-1", "col-2"};
String selection = "col-1 =? AND col-2=?";
String[] selectionArgs = {"apple","mango"};
String groupBy =col-3;
String having =" COUNT(col-4) > 5";
String orderBy = "col-2 DESC";
String limit = "15";
query(tableName, columns, selection, selectionArgs, groupBy, having, orderBy, limit);
db.query(
TABLE_NAME,
new String[] { TABLE_ROW_ID, TABLE_ROW_ONE, TABLE_ROW_TWO },
TABLE_ROW_ID + "=" + rowID,
null, null, null, null, null
);
TABLE_ROW_ID + "=" + rowID, here = is the where clause. To select all values you will have to give all column names:
or you can use a raw query like this
db.rawQuery("SELECT * FROM permissions_table WHERE name = 'Comics' ", null);
and here is a good tutorial for database.

SimpleAdapter needs an _id field

I got this :
Cursor c = db.query("Org", null, null, null, null, null, null);
which means I choose a table "Org", but together with this I need to make this :
Cursor c = db.rawQuery(" SELECT "+ id + " AS _id")
because SimpleAdapter need to have an _id field necessarily for some reason or it will crash with an error. How do I combine this 2 into one query?
The second parameter of the query function is the list of columns.
If you want to rename a column, you cannot just blindy return all columns but have to list the desired columns:
String[] columns = new String[] { id+" AS _id", "Name", "Color", "whatever..." };
Cursor c = db.query("Org", columns, null, null, null, null, null);
For your statement : Cursor c = db.query("Org", null, null, null, null, null, null); the second parameter is wrong, you shoukd mention the column names in it.
public Cursor query (boolean distinct, String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit)
Whereas for,
Cursor c = db.rawQuery(" SELECT "+ id + " AS _id from Org");
means that you Select id and create an alias of it using AS into _id, and you are selecting this id from Org table.
so now you will be able to access the result from this query from the column name _id, and in order to access the result use:
c.moveToFirst();
while (c.moveToNext())
{
System.out.println(c.getString(c.getColumnIndex("_id"));
}

Android SQLite database remove duplicates from query

I'm new to SQLite. I'm using this query in order to extract all rows from a column for a specific user:
Cursor c = db.query(true, TABLE, COLUMN, USER + "= '" + user + "'", null, null, null, null, null);
This is an example of table:
|group-----ID|
|------------|
|one-------me|
|one------you|
|two-------me|
|one-------me|
So the query for user "me" extracts "one, two, one". How can I filter the result in order to obtain a value just one time? Like "one, two"
Thanks
Use the Group By parameter with the appropriate column name:
Cursor c = db.query(true, TABLE, COLUMN, USER + "= '" + user + "'", null,
"group", null, null, null);
Since there are nine parameters in this method and three nearly identical methods...
public Cursor query(boolean distinct,
String table,
String[] columns,
String selection,
String[] selectionArgs,
String groupBy, /* this one */
String having,
String orderBy,
String limit)

Query only the first data from a table

I'm trying to query only the first data from the table.
Cursor img_cursor = db.query(
IMAGE_URL_TABLE_NAME,
new String[]{"small_img_url" , "large_img_url"},
null",
null, null, null, null);
Could somebody tell me how to implement a query where only the first data is retrieved from a table?
Solution
I think I solved the answer:
Cursor img_cursor = db.query(
IMAGE_URL_TABLE_NAME,
new String[]{"small_img_url" , "large_img_url"},
null",
null, null, null, null , "1");
I used limit 1 first, but the application crashed. Only if I pass the number as a String will it work. The query has 8 parameters while we're using the limit parameter.
limit 1
From Documentation:
public Cursor query (boolean distinct, String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit)
so, put your last argument to be "limit 1".
Cursor img_cursor = db.query(
IMAGE_URL_TABLE_NAME,
new String[]{"small_img_url" , "large_img_url"},
null,
null, null, null, "limit 1");

data type mismatch error when using ORDER BY

I've got an android app using a local sqlite database.
private SQLiteDatabase mDb;
when I run this query I get my Cursor over rows with pid equal to id, as desired:
mDb.query(true, PT_TABLE, new String[] {KEY_PID, KEY_TID},
KEY_PID+" = "+id, null, null, null, null, null);
when I run the following query, aiming to get that same result set, ordered by pid I get "android.database.sqlite.SQLiteException: datatype mismatch"
mDb.query(true, PT_TABLE, new String[] {KEY_PID, KEY_TID},
KEY_PID+" = "+id, null, null, null, null, KEY_PID+" DESC");
Any ideas?
It looks like you got just a little mixed up. According to the SQLiteDatabase.query documentation, the last argument is the LIMIT clause. The second to last is the ORDER BY clause.
Cursor query (boolean distinct,
String table,
String[] columns,
String selection,
String[] selectionArgs,
String groupBy,
String having,
String orderBy, // <-- ORDER BY
String limit)
EDIT
But, there is also another SQLiteDatabase.query where ORDER BY would be last
Cursor query (String table,
String[] columns,
String selection,
String[] selectionArgs,
String groupBy,
String having,
String orderBy)
This worked for me
String filter = MySQLiteHelper.JOB_ID + "=" + Integer.toString(jobID);
String orderBy = MySQLiteHelper.LOG_TIME + " DESC";
Cursor cursor = database.query(MySQLiteHelper.LOG_TABLE_NAME, logTableColumns,
filter, null, null, null, orderBy);
KEY_PID + " = " + "'" + id + "'"
Since Orderby is the second last parameter in the query;
your query would be like this
mDb.query(true, PT_TABLE, new String[] {KEY_PID, KEY_TID},
KEY_PID+" = "+id, null, null, null, KEY_PID+" DESC", null);
If I correctly understood your problem, try this.
String[] columns = new String[] {KEY_PID, KEY_TID};
String where = KEY_PID + " = " + Integer.toString(id);
String orderBy = KEY_PID + " DESC";
Cursor cursor = mDb.query(PT_TABLE, columns, where, null, null, null, orderBy);

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