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Android中提供的SQLiteDatabase類，其中的幾個方法返回的是rowid，這個rowid並不是插入的行號（row num或者說是RecNo），而是sqlite中自動維護的一個隱藏的列rowid，這個rowid和integer primary key autoincrement的欄位有什麼區別呢？

Android中的資料庫查詢API

我們以Android中提供的資料庫插入API：db.insert來說明，這個方法的返回值描述如下：

Returns:
the
 
 row ID of the newly inserted row, or -1 if an error occurred

經過驗證，這裡的row ID是是rowid，並不是插入的行號（row num或者說是RecNo）。下面我們假設integer primary key autoincrement的欄位的欄位名為id，如下圖：

RecNo和id：

rowid和id：

但是這個rowid屬於由sqlite自己維護的列，如果不顯式指定，即使使用select * from table也是不會出現的。
如果要查詢rowid必須使用select rowid,* from table

RecNo和id區別

這個比較簡單，RecNo是單調遞增，無論資料表怎麼變化，只要查詢結果的第一條就是1（表頭為0），當然這個和表沒有任何關係，如果order by是由使用者決定的，所以不存在對應關係。
而id也是單調遞增的，如果刪除了某一條記錄，id還是會繼續遞增，不會調整，id屬於資料表的欄位，和資料有對應關係，無論怎麼查詢，id都不會變化。
比如select rowid,* from table order by id desc結果：

結論：RecNo就是查詢結果的一個標號而已。

rowid和id區別

這個rowid和每條資料是有密切關係的
比如select rowid,* from table order by id desc

我們參考sqlite官網提供說明：

The AUTOINCREMENT Keyword

If a column has the type INTEGER PRIMARY KEY AUTOINCREMENT then a slightly different ROWID selection algorithm is used. The ROWID chosen for the new row is at least one larger than the largest ROWID that has ever before existed in that same table. If the table has never before contained any data, then a ROWID of 1 is used. If the table has previously held a row with the largest possible ROWID, then new INSERTs are not allowed and any attempt to insert a new row will fail with an SQLITE_FULL error. Only ROWID values from previously transactions that were committed are considered. ROWID values that were rolled back are ignored and can be reused.

SQLite keeps track of the largest ROWID that a table has ever held using an internal table named “sqlite_sequence”. The sqlite_sequence table is created and initialized automatically whenever a normal table that contains an AUTOINCREMENT column is created. The content of the sqlite_sequence table can be modified using ordinary UPDATE, INSERT, and DELETE statements. But making modifications to this table will likely perturb the AUTOINCREMENT key generation algorithm. Make sure you know what you are doing before you undertake such changes.

The behavior implemented by the AUTOINCREMENT keyword is subtly different from the default behavior. With AUTOINCREMENT, rows with automatically selected ROWIDs are guaranteed to have ROWIDs that have never been used before by the same table in the same database. And the automatically generated ROWIDs are guaranteed to be monotonically increasing. These are important properties in certain applications. But if your application does not need these properties, you should probably stay with the default behavior since the use of AUTOINCREMENT requires additional work to be done as each row is inserted and thus causes INSERTs to run a little slower.

Note that “monotonically increasing” does not imply that the ROWID always increases by exactly one. One is the usual increment. However, if an insert fails due to (for example) a uniqueness constraint, the ROWID of the failed insertion attempt might not be reused on subsequent inserts, resulting in gaps in the ROWID sequence. AUTOINCREMENT guarantees that automatically chosen ROWIDs will be increasing but not that they will be sequential.

Because AUTOINCREMENT keyword changes the behavior of the ROWID selection algorithm, AUTOINCREMENT is not allowed on WITHOUT ROWID tables or on any table column other than INTEGER PRIMARY KEY. Any attempt to use AUTOINCREMENT on a WITHOUT ROWID table or on a column other than the INTEGER PRIMARY KEY column results in an error.

簡單抽取關鍵的內容就是：id如果設定為integer primary key autoincrement的欄位，則不需要自己手動賦值，插入時傳入null由資料庫來設定其值，這個值資料庫預設設定為rowid的最大值+1（也可以自己手動設定，但不要引起重複等問題）
rowid：單調遞增，直到達到最大值後，複用已經刪除的rowid作為新的值
id：可以自行設定，或者是資料庫自動設定（rowid的最大值+1），到達最大值後不復用已經刪除的值，拋異常SQLITE_FULL 。

這裡可以得出結論：rowid和id不一樣，不要混用。

特殊情況

如果integer primary key autoincrement的欄位名為rowid，那麼怎麼查詢rowid？
答案是相同的方法，rowid不是存在表中的，而是在sqlite_sequence中，如果查詢，則自己設定的rowid會起別名：

不查詢rowid則不會起別名：