ECOB 支持通过SELECT...INTO将 SQL 查询结果存储到二维数组。 示例语句如下所示: EXECSQLcreatetablet1(id numbernotnullprimarykey,name varchar2(50)notnull,unique(name))partitionbyhash(id)partitions8;//arr_id 一维数组intarr_id[2];EXECSQLselectidinto:arr_idfromt1whereid>1andid<4orderbyid;printf...
结果变成了:Using index,表示 全程走索引,不回表,性能更优。 实际应用场景 报表查询: 如果你常常只需要查某个字段的统计,比如 SELECT age FROM users WHERE name = ?,可以考虑用覆盖索引加速。 分页查询: 比如SELECT id FROM table WHERE xxx ORDER BY id LIMIT 100,如果只需要 id,那么走覆盖索引非常高效。
AlwaysOn 可用性群組支持查詢可讀取次要複本上的數據行存放區索引。 Multiple Active Result Sets (MARS) 支援列存儲索引。 全新動態管理檢視sys.dm_db_column_store_row_group_physical_stats (Transact-SQL)提供資料列群組層級的效能疑難排解資訊。 數據行存放區索引上的所有查詢都可以在批次模式中執行。 先前,只有...
Sales表(SelesID,SalesDate,SalesPersonID,ProductID,Qty)的外键列(ProductID)上创建了一个索引,假设ProductID列是一个高选中性列,那么任何在where子句中使用索引列(ProductID)的select查询都会更快,如果在外键上没有创建索引,将会发生全部扫描,但还有办法可以进一步提升查询性能。 Sales表有10,000行记录,下面的SQL语...
SELECT DISTINCT often your results will include many duplicate values. If you want to select all the unique values from a column, you can use the DISTINCT keyword. SELECT DISTINCT language FROM films; Learning to COUNT 统计“记录” What if you want to count the number of employees in your ...
1SELECTEmailFROM2(SELECTEmail,COUNT(id)ASnum3FROMPerson4GROUPBYEmail)AStmp5WHEREnum>1; 183. Customers Who Never Order[e] 一、表信息 假设一个网站上包含如下两张表:顾客表和订单表 Suppose that a website contains two tables, the Customers table and the Orders table. ...
= first_row ] [ , LASTROW = last_row ] [ , MAXERRORS = maximum_errors ] [ , ERRORFILE = 'file_name' ] [ , ERRORFILE_DATA_SOURCE = 'data_source_name' ] [ , ROWS_PER_BATCH = rows_per_batch ] [ , ORDER ( { column [ ASC | DESC ] } [ , ...n ] ) [ UNIQUE ] ]...
UNIQUE and PRIMARY KEY constraints are always enforced. When importing into a character column that is defined with a NOT NULL constraint, BULK INSERT inserts a blank string when there's no value in the text file. At some point, you must examine the constraints on the whole table. If the...
The name that was used on the CREATE ASSEMBLY statement. class_name - must match a value in the assembly_name column of SELECT * FROM sys.assembly_modules;. Often the value contains an embedded period or dot. In such cases, the Transact-SQL syntax requires that the value is bounded with...
CREATE UNIQUE INDEX index1 ON schema1.table1 (column1 DESC, column2 ASC, column3 DESC); 主要方案: 从Azure SQL 数据库和 Azure SQL 托管实例中的 SQL Server 2016(13.x)开始,可以在列存储索引上使用非聚集索引来提高数据仓库查询性能。 有关详细信息,请参阅 列存储索引 - 数据仓库。 有关其他类型...