select product_id from orders where id = 100 union select product_id from orders where id = 200; 正解: select product_id from orders where id = 100 union all select product_id from orders where id = 200; 原因: union:对两个结果集进行并集操作,不包括重复行,相当于distinct,同时进行默认规则...
如果指定或WITH (NOEXPAND)指定WITH (NOEXPAND, INDEX( <index_value> [ , *...n* ] ) ),视图也会保持精简状态。 有关查询提示 NOEXPAND的详细信息,请参阅 使用NOEXPAND。 该提示仅影响语句SELECT部分中的视图,包括这些视图,INSERTUPDATEMERGE以及DELETE语句。 FAST integer_value 指定查询经过优化,以便快速检索...
SELECT *,ROW_NUMBER() OVER (PARTITION BY CustomerID ORDER BY OrderDate DESC) AS RankFROM Orders)SELECT *FROM RankedOrdersWHERE Rank = 1;优势:窗口函数在服务器内高效排序,减少I/O开销。2. 利用 `WITH (NOLOCK)` 处理高并发读场景(谨慎使用)场景:允许脏读(读取未提交数据),提升查询速度,适用于允许...
建立函数索引: create index IND_WF_WORK_ITEM_HS1 on wf_work_item(nvl(operid,'1')); 优化后SQL语句为: select DECODE(NVL(OPERID, '0'), '0', '岗位待办', '个人待办') TASK, PROCESS_DEF_NAME, DECODE(IS_RETURN, '1', '<span style="color:red">' || BAE007 || '</span>', BAE0...
CREATEPROCEDUREMoveOrg ( @oldMgrNVARCHAR(256), @newMgrNVARCHAR(256) )ASBEGINDECLARE@nold HIERARCHYID, @nnew HIERARCHYID;SELECT@nold = OrgNodeFROMHumanResources.EmployeeDemoWHERELoginID = @oldMgr;SETTRANSACTIONISOLATIONLEVELSERIALIZABLE;BEGINTRANSACTION;SELECT@nnew = OrgNodeFROMHumanResources.EmployeeDemo...
无法在此数据库中运行 SELECT INTO。数据库所有者必须运行 sp_dboption 以启用此选项。 270 16 否 不能修改对象 '%.*ls'。 271 16 否 不能修改列 "%.*ls",因为它是计算列,或者是 UNION 运算符的结果。 272 16 否 不能更新时间戳列。 273 16 否 不能将显式值插入时间戳列。请对列列表使用 INSERT...
當 ODBC 函數{fn CONVERT()}轉換成 ODBC 資料類型 SQL_TIMESTAMP、SQL_DATE、SQL_TIME、SQLDATE、SQL_TYPE_TIME 和 SQL_TYPE_TIMESTAMP 時,會使用樣式 121 (與語言無關的 YMD 格式)。低 Datetime 內部函數,例如DATEPART不需要字串輸入值是有效的 datetime 常值。 例如,SELECT DATEPART (year, '2007/05-30...
have the same key to create a result row with combined columns from both tables. eg. Copy SELECTtitle, ratingFROMmoviesJOINboxofficeONmovies.id=boxoffice.movie_idORDERBYratingDESC; 5. OUTER JOINs# Copy %SelectquerywithLEFT/RIGHT/FULLJOINsonmultiple tablesSELECTcolumn, another_column, ...FROMmy...
added might be too small to trigger a statistics update. If statistics aren't up-to-date and queries select from the most recently added rows, the current statistics don't have cardinality estimates for these new values. This can result in inaccurate cardinality estimates and slow query ...
CREATE TABLE T(a int, b real, c as getdate(), d as a+b) CREATE VIEW VT WITH SCHEMABINDING AS SELECT a, b, c, d FROM dbo.T SELECT object_id('VT'), COLUMNPROPERTY(object_id('VT'),'b','IsPrecise') You can experiment with COLUMNPROPERTY to find out whether the other columns...