I have two table
table 1(t1)
mid INTEGER PRIMARY KEY
Name TEXT
table 2(t2)
id INTEGER PRIMARY KEY
mid INTEGER
Amount INT
Token TEXT NOT NULL
I need a new table which join both these table based on the token value.
New Table
mid Amount Name Token.
My Answer:
String Sql_Query="SELECT t1.Name, t2.Amount, t2.mid, t2.Token from t1 INNER JOIN t2 ON t1.mid = t2.mid where t2.Token="abc" ";
db.rawQuery(Sql_Query,null);
End up getting empty array.
I got the solution. If anyone needs solution he/she can use below code
db.rawquery("SELECT t1.Name, t2.Amount, t2.mid, t2.Token from t1 INNER JOIN t2 ON t1.mid = t2.mid",null);
Related
I have an application, where I am detecting the type of a particular column at run-time, on page load. Please refer the below code:
public String fncCheckColumnType(String strColumnName){
db = this.getWritableDatabase();
String strColumnType = "";
Cursor typeCursor = db.rawQuery("SELECT typeof (" + strColumnName +") from tblUsers, null);
typeCursor.moveToFirst();
strColumnType = typeCursor.getString(0);
return strColumnType;
}
The above method simply detects the type of column with column Name 'strColumnName'. I am getting the type of column in this case.
Now, I want to change the column type to TEXT if I am receiving INTEGER as the column type. For this, I tried the below code:
public String fncChangeColumnType(String strColumnName){
db = this.getWritableDatabase();
String newType = "";
Cursor changeCursor = db.rawQuery("ALTER TABLE tblUsers MODIFY COLUMN " + strColumnName + " TEXT", null);
if (changeCursor != null && changeCursor.moveToFirst()){
newType = changeCursor.getString(0);
}
return newType;
}
But while executing the 'fncChangeColumnType' method, I am getting this error, android.database.sqlite.SQLiteException: near "MODIFY": syntax error (code 1): , while compiling: ALTER TABLE tblUsers MODIFY COLUMN UserID TEXT
NOTE: I also replaced 'MODIFY' with 'ALTER', but still getting the same error.
Please check if this is the right method to change the type dynamically.
Please respond back if someone has a solution to this.
Thanks in advance.
In brief, the solution could be :-
Do nothing (i.e. take advantage of SQLite's flexibility)
you could utilise CAST e.g. CAST(mycolumn AS TEXT) (as used below)
Create a new table to replace the old table.
Explanations.
With SQLite there are limitations on what can be altered. In short you cannot change a column. Alter only allows you to either rename a table or to add a column. As per :-
SQL As Understood By SQLite - ALTER TABLE
However, with the exception of a column that is an alias of the rowid column
one defined with ?? INTEGER PRIMARY KEY or ?? INTEGER PRIMARY KEY AUTOINCREMENT or ?? INTEGER ... PRIMARY KEY(??) (where ?? represents a valid column name)
you can store any type of value in any type of column. e.g. consider the following (which stores an INTEGER, a REAL, a TEXT, a date that ends up being TEXT and a BLOB) :-
CREATE TABLE IF NOT EXISTS example1_table (col1 BLOB);
INSERT INTO example1_table VALUES (1),(5.678),('fred'),(date('now')),(x'ffeeddccbbaa998877665544332211');
SELECT *, typeof(col1) FROM example1_table;
The result is :-
As such is there a need to change the column type at all?
If the above is insufficient then your only option is to create a new table with the new column definitions, populate it if required from the original table, and to then replace the original table with the new table ( a) drop original and b)rename new or a) rename original, b) rename new and c) drop original)
e.g. :-
DROP TABLE IF EXISTS original;
CREATE TABLE IF NOT EXISTS original (mycolumn INTEGER);
INSERT INTO original VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(0);
-- The original table now exists and is populated
CREATE TABLE IF NOT EXISTS newtable (mycolumn TEXT);
INSERT INTO newtable SELECT CAST(mycolumn AS TEXT) FROM original;
ALTER TABLE original RENAME TO old_original;
ALTER TABLE newtable RENAME TO original;
DROP TABLE IF EXISTS old_original;
SELECT *,typeof(mycolumn) FROM original;
The result being :-
i think the sql query statement is wrong ,try
ALTER TABLE tblUsers MODIFY COLUMN id TYPE integer USING (id::integer);
instead of id use column name....
hope this helps....
EDIT:
"ALTER TABLE tblUsers MODIFY COLUMN "+strColumnName+" TYPE integer USING ("+strColumnName+"::integer);"
We have a requirement where some fields in a table need to have the same value as their ID. Unfortunately, we currently have to insert a new record and then, if needed, run another update to set the duplicate field (ID_2) value to equal the ID.
Here is the Android Sqlite code:
mDb.beginTransaction();
// ... setting various fields here ...
ContentValues contentValues = new ContentValues();
contentValues.put(NAME, obj.getName());
// now insert the record
long objId = mDb.insert(TABLE_NAME, null, contentValues);
obj.setId(objId);
// id2 needs to be the same as id:
obj.setId2(objId);
// but we need to persist it so we update it in a SECOND call
StringBuilder query = new StringBuilder();
query.append("update " + TABLE_NAME);
query.append(" set " + ID_2 + "=" + objId);
query.append(" where " + ID + "=" + objId);
mDb.execSQL(query.toString());
mDb.setTransactionSuccessful();
As you can see, we are making a second call to set ID_2 to the same value of ID. Is there any way to set it at INSERT time and avoid the second call to the DB?
Update:
The ID is defined as follows:
ID + " INTEGER PRIMARY KEY NOT NULL ," +
The algorithm used for autoincrementing columns is documented, so you could implement it manually in your code, and then use the new value for the INSERT.
This is quite a ugly hack, but it may be possible :
with id_table as (
select coalesce(max(seq), 0) + 1 as id_column
from sqlite_sequence
where name = 'MY_TABLE'
)
insert into MY_TABLE(ID_1, ID_2, SOME, OTHER, COLUMNS)
select id_column, id_column, 'SOME', 'OTHER', 'VALUES'
from id_table
It only works if the table ID is an AUTOINCREMENT, and is therefore managed via the documented sqlite_sequence table.
I also have no idea what happen in case of concurrent executions.
You could use an AFTER INSERT TRIGGER e.g.
Create your table (at least for this example) so that ID_2 is defined as INTEGER DEFAULT -1 (0 or any negative value would be ok)
e.g. CREATE TABLE IF NOT EXISTS triggertest (_id INTEGER PRIMARY KEY ,name TEXT ,id_2 INTEGER DEFAULT -1);
Then you could use something like (perhaps when straight after the table is created, perhaps create it just before it's to be used and drop it after done with it ) :-
CREATE TRIGGER triggertesting001
AFTER INSERT ON triggertest
BEGIN
UPDATE triggertest SET id_2 = `_id`
WHERE id_2 = -1;
END;
Drop using DROP TRIGGER IF EXISTS triggertesting001;
Example usage (testing):-
INSERT INTO triggertest (name) VALUES('Fred');
INSERT INTO triggertest (name) VALUES('Bert');
INSERT INTO triggertest (name) VALUES('Harry');
Result 1 :-
Result 2 (trigger dropped inserts run again ):-
Result 3 (created trigger) same as above.
Result 4 (ran inserts for 3rd time) catch up i.e. 6 rows updated id_2 with _id.
I'd strongly suggest reading SQL As Understood By SQLite - CREATE TRIGGER
Alternative solution
An alternative approach could be to simply use :-
Before starting transaction, retrieve mynextid from table described below
ContentValues contentValues = new ContentValues();
contentValues.put(ID,mynextid);
contentvalues.put(ID_2,mynextid++);
contentValues.put(NAME, obj.getName());
Then at end of the transactions update/store the value of mynextid in a simple single column, single row table.
i.e. you are managing the id's (not too dissimilar to how SQLite manages id's when 'AUTOINCREMENT' is specified)
I have a query with a subquery that returns multiple rows.
I have a table with lists and a table with users. I created a many-to-many table between these two tables, called list_user.
LIST
id INTEGER
list_name TEXT
list_description TEXT
USER
id INTEGER
user_name TEXT
LIST_USER
id INTEGER
list_id INTEGER
user_id INTEGER
My query with subquery
SELECT * FROM user WHERE id = (SELECT user_id FROM list_user WHERE list_id = 0);
The subquery works (and I use it in code so the 0 is actually a variable) and it returns multiple rows. But the upper query only returns one row, which is pretty logical; I check if the id equals something and it only checks against the first row of the subquery.
How do I change my statement so I get multiple rows in the upper query?
I'm surprised the = works in SQLite. It would return an error in most databases. In any case, you want the in statement:
SELECT *
FROM list
WHERE id in (SELECT user_id FROM list_user WHERE list_id = 0);
For a better performance, use this query:
SELECT LIST.ID,
LIST.LIST_NAME,
LIST.LIST_DESCRIPTION
FROM LIST,
USER,
LIST_USER
WHERE LIST.ID = LIST_USER.USER_ID = USER.ID AND
LIST.LIST_ID = 0
Pretend I have a table with 2 columns. _id and name. _id is the primary key and I do not want to set this value manually. I want to perform an insert of name="john," and let the program create my own _id. I am unclear what "index" to use when inserting and how many question marks to use. Does this code do the job? Should the index for john be 1 or 2?
String TABLENAME = "table";
SQLiteStatement statement = db.compileStatement("INSERT INTO "+TABLENAME+" VALUES(?);");
statement.bindString(1,"john");
statement.executeInsert();
Next, say I want to manually set my own _id value. Would I change the code to:
String TABLENAME = "table";
SQLiteStatement statement = db.compileStatement("INSERT INTO "+TABLENAME+" VALUES(?,?);");
statement.bindLong(1,666); //Manual _id.
statement.bindString(2,"john");
statement.executeInsert();
Your first example where you provide only the name will not work:
sqlite> create table test (i integer primary key autoincrement, j text);
sqlite> insert into test values ('asd');
Error: table test has 2 columns but 1 values were supplied
sqlite> insert into test values (null, 'asd');
sqlite> select * from test;
1|asd
sqlite> insert into test (j) values ('asd');
sqlite> select * from test;
1|asd
2|asd
so you need to identify the name column as the destination of the sole value this way, (or as you mentioned in your comment pass null):
SQLiteStatement statement = db.compileStatement("INSERT INTO "+TABLENAME+" (name) VALUES(?);");
Your second example should work fine.
This would apply to some table created this way:
create table SomeTable (_id integer primary key autoincrement, name text)
Then
SQLiteStatement statement = db.compileStatement("INSERT INTO "+TABLENAME+" VALUES(null,?);");
statement.bindString(1,"john");
Should also work.
Im getting this error when i try to access my View
I've built my database/View using this
CREATE TABLE Boxer(
BoxerId INTEGER PRIMARY KEY AUTOINCREMENT,
Firstname NVARCHAR(50) NOT NULL,
Lastname NVARCHAR(50) NOT NULL
);
CREATE TABLE Match(
MatchId INTEGER PRIMARY KEY AUTOINCREMENT,
BoxerA INTEGER NOT NULL FOREIGN KEY REFERENCES Boxer(BoxerId),
BoxerB INTEGER NOT NULL FOREIGN KEY REFERENCES Boxer(BoxerId),
MatchDate date NOT NULL DEFAULT GETDATE(),
NumberOfRounds INTEGER NOT NULL DEFAULT 12
);
CREATE TABLE Round(
RoundId INTEGER PRIMARY KEY AUTOINCREMENT,
MatchId INTEGER NOT NULL FOREIGN KEY REFERENCES Match(MatchId),
BoxerA INTEGER NOT NULL DEFAULT 0,
BoxerB INTEGER NOT NULL DEFAULT 0,
Position INTEGER NOT NULL
);
/*
Building a view which dislpays matches with boxers names and total scores
*/
CREATE VIEW MatchDetail AS
SELECT Match.MatchId, A.BoxerId AS IdA, B.BoxerId AS IdB, A.Firstname + ' ' + A.Lastname AS NameA, B.Firstname + ' ' + B.Lastname AS NameB,
(SELECT SUM(R.BoxerA) AS Score FROM Round AS R WHERE (R.MatchId = Match.MatchId)) AS ScoreA,
(SELECT SUM(R.BoxerB) AS Score FROM Round AS R WHERE (R.MatchId = Match.MatchId)) AS ScoreB,
Match.MatchDate, Match.NumberOfRounds
FROM Boxer AS A INNER JOIN Match ON A.BoxerId = Match.BoxerA INNER JOIN Boxer AS B ON Match.BoxerB = B.BoxerId
I've pretty much built my app so far using the notepad example so I then call my DbHelper
Cursor MatchesCursor = mDbHelper.fetchAllMatchDetails();
This then calls the query
public Cursor fetchAllMatchDetails(){
return mDb.query(VIEW_MATCHDETAIL, new String[] {
"MatchId"
}, null, null, null, null, null);
}
VIEW_MATCHDETAIL is defined as a string = "MatchDetail"
and it's here where it crashes saying
no such table MatchDetail: while compiling SELECT MatchId FROM MatchDetail
anyone had this problem before?
You have some beautiful SQL there. Unfortunately only the first line of sql will be executed in SQLiteDatabase.execSQL. The rest will be ignored silently (convenient eh?). Split up the statements manually like this:
https://github.com/browep/fpt/blob/master/src/com/github/browep/nosql/NoSqlSqliteOpener.java
or if you like to keep your sql in a separate file, try this:
String sqlText = getSqlText();
for(String sqlStmt : sqlText.split(";"))
myDb.execSQL(slqStmt + ";");
What stands out to me is the use of datatypes like NVARCHAR(50). SQLite only has a very simple set of datatypes. I'm surprised it doesn't throw an exception when you install the app. Try using simply TEXT instead.
If you cannot access a database that you know you have initialized, try passing the Context from the Activity that created the table to the class trying to query the table. Use that Context as part of your connection initialization.