[英]sqlite rawquery not working correctly
我有兩個表,它們的名稱分別是個人資料和消息。 我嘗試從SQL獲取與profileId相關的配置文件數據和最后一條消息。
SQLiteDatabase db = this.getReadableDatabase();
String selectQuery = "select " +
"profiles.profileId," +
"profiles.profileName," +
"profiles.profileImgPath," +
"profiles.profileStatus," +
"messages.messageContent," +
"messages.messageTime " +
"from profiles left join messages on profiles.profileId=messages.profileId " +
"group by profiles.profileId " +
"order by messages.messageId DESC;";
Cursor c = db.rawQuery(selectQuery, null);
Log.i("query",selectQuery);
if (c.moveToFirst()) {
do {
Log.i("gokberksql", c.getString(1) + "x" + c.getString(4));
} while (c.moveToNext());
}
gokberksql﹕ sinanxKanka naber
但需要退貨
gokberksql﹕ sinanxIyi senden naber
另外,此查詢在我的計算機編輯器中運行良好,但android結果不正確。
您應該在查詢中選擇最大messageTime。 這將為您提供與包含最大值的列在同一行中的列的值。
String selectQuery = "select " +
"profiles.profileId," +
"profiles.profileName," +
"profiles.profileImgPath," +
"profiles.profileStatus," +
"messages.messageContent," +
"max(messages.messageTime) as messageTime " + // <- here
"from profiles " +
"left join messages on profiles.profileId = messages.profileId " +
"group by profiles.profileId" +
"order by profiles.profileId, messages.messageId DESC;";
請注意,此行為是在SQLite 3.7.11版中引入的,該版本在API 16(JellyBean)中成為標准。 如果需要支持API 15或更早版本,則可能必須使用其他查詢。
為什么要有一個由profiles.profileId組成的組,在這種情況下就不需要了,因為您沒有對profileId組進行任何聚合。 試試看
String selectQuery = "select " +
"profiles.profileId," +
"profiles.profileName," +
"profiles.profileImgPath," +
"profiles.profileStatus," +
"messages.messageContent," +
"messages.messageTime " +
"from profiles left join messages on profiles.profileId=messages.profileId " +
"order by profiles.profileId, messages.messageId DESC;";
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