Oracle DBA_EXTENTS視圖 與 DBA_SEGMENTS視圖

Oracle DBA_EXTENTS視圖 與 DBA_SEGMENTS視圖
DBA_EXTENTS describes the extents comprising the segments in all tablespaces in the database. Note that if a datafile (or entire tablespace) is offline in a locally managed tablespace, you will not see any extent information. If an object has extents in an online file of the tablespace, you will see extent information about the offline datafile. However, if the object is entirely in the offline file, a query of this view will not return any records. Related View USER_EXTENTS describes the extents comprising the segments owned by the current user's objects. This view does not display the OWNER, FILE_ID, BLOCK_ID, or RELATIVE_FNO columns.      也就是說DBA_EXTENDS描述的是資料庫所有資料表空間中段的擴充資訊。使用DBA_EXTENDS必須保證相應的資料檔案處於online狀態，否則無法返回任何記錄。對於一用於，常使用的是USER_EXTENTS視圖，比DBA_EXTENDS視圖少幾個欄位。 -------------------------------------------------------------------------------------------------------------------------------- DBA_SEGMENTS describes the storage allocated for all segments in the database. Related View USER_SEGMENTS describes the storage allocated for the segments owned by the current user's objects. This view does not display the OWNER, HEADER_FILE, HEADER_BLOCK, or RELATIVE_FNO columns.      DBA_SEGMENTS 視圖描述的是資料庫中所有段的儲存和分配資訊。 　　段包含多個擴充區，擴充區是與資料相關的使用者可見的最底層的視圖，通過這兩個視圖，我們可以知道一條記錄所在的資料表空間，資料檔案號和分區。還可以知道各儲存段的大小和擴充區資訊。