如何从sql数据库中获取唯一值

Question

The following code gives all values from database even duplicate values.

return database.query("contacts", new String[] {"_id", "name"}, 
     null, null, null, null, "name");

how can i get distinct values from above code

Answer 1

Use the overload of query that takes a boolean as first parameter and remove the _id column from the select:

return database.query(true, "contacts", new String[] {"name"}, 
                      null, null, null, null, "name", null);

The _id column is supposed to be unique, so including it in your query will lead to the distinct having no effect.

Answer 2

使用distinct关键字，这将返回数据库中的唯一记录。

db.rawQuery("Select DISTINCT from table_name",null);

Answer 3

use this query:

public Cursor query (boolean distinct, String table, 
                 String[] columns, String selection, 
                 String[] selectionArgs, String groupBy, 
                 String having, String orderBy, String limit)

set the first param to true and do not use youre primarey key in selection. it will be always unique...