how to use rawQuery in android

问题:

I have a database table with 3 columns: id, name, permission.

It looks like this:

1 Comics fun

2 Communication talk

3 Comics watch

I am trying to get the permission where the name is comics. I am using the following code in my database class(AppData.java):

private final static String DB_NAME = "safety_app_database"; // the name of our database private final static int DB_VERSION = 1; // the version of the database  // the names for our database columns private final String TABLE_NAME = "permissions_table"; private final String ID = "id"; private final String NAME = "name"; private final String PERMISSION = "permission"; 

and the method

public Cursor getData(){         return db.rawQuery("SELECT permission FROM permissions_table WHERE name = 'Comics', null);     } 

and I'm calling this in my main class (safety.java). AppData is referencing AppData.java

appData.getData(); 

Is this the correct way to do it? I am unsure, and it is giving me an error whenever I try to call the sql query.

回答1:

One typo mistake, you are not closing sql string with ". try this.

return db.rawQuery("SELECT permission FROM permissions_table WHERE name = 'Comics' ", null); 

[EDIT: JAR belongs to 'Android 2.2' which does not allow modifications to source attachments on its entries]

The Jar of this class file blongs to container Android 2.0.1 which does not allow modifications

回答2:

There is no need for a raw query. You can use one of the recommended SQLiteDatabase query methods and it would look like this:

db.query("permissions_table", new String [] {permission}, "name = \'Comics\'", null, null, null, null); 

回答3:

Try the following approach:

public Cursor getData(String arg) {    return db.rawQuery("SELECT permission FROM `permissions_table` WHERE name ="+arg, null); } 

Then just call the above method with the right parameter like this:

Cursor cursor;  cursor  =  getData ( "Comic" ); 

回答4:

To execute queries, there are two methods: Execute db.rawQuery method Execute db.query method To execute a raw query to retrieve all departments:

Cursor getAllDepts()   {    SQLiteDatabase db=this.getReadableDatabase();    Cursor cur=db.rawQuery("SELECT "+colDeptID+" as _id,          "+colDeptName+" from "+deptTable,new String [] {});     return cur;   } 

The rawQuery method has two parameters: String query: The select statement String[] selection args: The arguments if a WHERE clause is included in the select statement Notes The result of a query is returned in Cursor object. In a select statement if the primary key column (the id column) of the table has a name other than _id, then you have to use an alias in the form SELECT [Column Name] as _id cause the Cursor object always expects that the primary key column has the name _id or it will throw an exception . Another way to perform a query is to use a db.query method. A query to select all employees in a certain department from a view would be like this:

public Cursor getEmpByDept(String Dept) {    SQLiteDatabase db=this.getReadableDatabase();    String [] columns=new String[]{"_id",colName,colAge,colDeptName};    Cursor c=db.query(viewEmps, columns, colDeptName+"=?",          new String[]{Dept}, null, null, null);    return c;   } 

The db.query has the following parameters: String Table Name: The name of the table to run the query against String [ ] columns: The projection of the query, i.e., the columns to retrieve String WHERE clause: where clause, if none pass null String [ ] selection args: The parameters of the WHERE clause String Group by: A string specifying group by clause String Having: A string specifying HAVING clause String Order By by: A string Order By by clause

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