SQL Server 查詢最佳化工具不僅能選擇最低資源成本的執行計畫,也能選擇以資源成本合理為使用者提供結果的計畫,還有最快傳回結果的計畫。 例如,一般平行處理查詢時,需使用比循序處理時使用更多的資源,但完成的速度較快。 如果不會對伺服器造成嚴重負載,SQL Server 查詢最佳化工具將會使用平行執行計畫來傳回結果。
物理运算符包括Dynamic、Fetch Query、Keyset、Population Query、Refresh Query和Snapshot。 DeclareDeclare 运算符用于分配查询计划中的局部变量。 Declare是一个语言元素。 删除Delete运算符将从对象中删除满足“属性”窗格中的可选谓词的行。 Deleted Scan在触发器中,Deleted Scan运算符扫描已删除的表。
The SQL Server Query Optimizer doesn't choose only the execution plan with the lowest resource cost; it chooses the plan that returns results to the user with a reasonable cost in resources and that returns the results the fastest. For example, processing a query in parallel typically uses ...
DECLARE cursor_name CURSOR [ LOCAL | GLOBAL ] [ FORWARD_ONLY | SCROLL ] [ STATIC | KEYSET | DYNAMIC | FAST_FORWARD ] [ READ_ONLY | SCROLL_LOCKS | OPTIMISTIC ] [ TYPE_WARNING ] FOR select_statement [ FOR UPDATE [ OF column_name [ ,...n ] ] ] [;] 参数解释 cursor_...
Dynamic Cursor in plsql (2) 获取cursor行数:当游标被打开后,%ROWCOUNT归零。第一次提取之前,cursor_name%ROWCOUNT返回0。此后,它返回的fetch到的行数。完成一次fetch操作后,count+1。获取cursor 列数:1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 ...
Transact-SQL cursors support forward-only static, keyset-driven, and dynamic cursors. The database API cursor models assume that static, keyset-driven, and dynamic cursors are always scrollable. When a database API cursor attribute or property is set to forward-only, SQL Server implements this ...
[FORWARD_ONLY|SCROLL] [STATIC|KEYSET|DYNAMIC|FAST_FORWARD] [READ_ONLY|SCROLL_LOCKS|OPTIMISTIC] FOR select_statement cursor_name:指定要声明游标的名称 select_statement:指定游标所用结果集的SELECT语句 Demo 01: DECLARE cursor_users CURSOR FOR SELECT * FROM Users; ...
1DECLAREcursor_nameCURSOR[LOCAL | GLOBAL]2[FORWARD_ONLY | SCROLL]3[STATIC | KEYSET | DYNAMIC | FAST_FORWARD]4[READ_ONLY | SCROLL_LOCKS | OPTIMISTIC]5[TYPE_WARNING]6FORselect_statement7[FOR UPDATE [ OF column_name [ ,...n]] ]8[;] ...
DECLARE CURSOR如果使用 Transact-SQL 语法未指定READ_ONLY,OPTIMISTIC或者SCROLL_LOCKS默认值如下所示: SELECT如果语句不支持更新(权限不足、访问不支持更新的远程表等),则游标为 READ_ONLY。 STATIC 和FAST_FORWARD 游标默认为 READ_ONLY。 DYNAMIC 和KEYSET 游标默认为 OPTIMISTIC。 游标名称只能由其他 Transact-SQL ...
Transact-SQL cursors support forward-only static, keyset-driven, and dynamic cursors. The database API cursor models assume that static, keyset-driven, and dynamic cursors are always scrollable. When a database API cursor attribute or property is set to forward-only, SQL Server implements this ...