十三、sql server not exists exists : 强调的是是否返回结果集,不要求知道返回什么, 比如: select name from student where sex = 'm' and mark exists(select 1 from grade where ...) ,只要 exists引导的子句有结果集返回,那么exists这个条件就算成立了,大家注意返回的字段始终为1,如果改成“select 2 from...
IF EXISTS(SELECT * FROM sys.indexes WHERE object_id = object_id('schema.tablename') AND NAME ='indexname') DROP INDEX indexname ON SCHEMA.tablename; CREATE INDEX indexname ON SCHEMA.tablename(columnlist); Why not simply: Create Index IndexName on schema.tablename (columnlist) with (drop...
The Database Engine doesn't allow creating a unique index on columns that already include duplicate values, whether or not IGNORE_DUP_KEY is set to ON. If this is attempted, the Database Engine displays an error message. Duplicate values must be removed before a unique index can be created...
To create a unique index on a table, using: SQL Server Management Studio Transact-SQL Before You Begin Benefits of a Unique Index Multicolumn unique indexes guarantee that each combination of values in the index key is unique. For example, if a unique index is created on a combination ofLas...
A filtered index is an optimized disk-based rowstore nonclustered index especially suited to cover queries that select from a well-defined subset of data.
The Database Engine doesn't allow creating a unique index on columns that already include duplicate values, whether or not IGNORE_DUP_KEY is set to ON. If this is attempted, the Database Engine displays an error message. Duplicate values must be removed before a unique index can be created...
To create a unique index on a table, using: SQL Server Management Studio Transact-SQLBefore You BeginBenefits of a Unique IndexMulticolumn unique indexes guarantee that each combination of values in the index key is unique. For example, if a unique index is created on a combination of LastNa...
所有选项在 Azure SQL 数据库中均可用。CREATE CLUSTERED COLUMNSTORE INDEX创建一个聚集列存储索引,并按列压缩和存储其中的所有数据。 该索引包含表中的所有列,并且存储整个表。 如果现有表是堆或聚集索引,则会将其转换为聚集列存储索引。 如果该表已作为聚集列存储索引存储,则会删除并重新生成现有索引。
WHERE 子句空值SQL Server 2016 (13.x) ORDER 子句SQL Server 2016 (13.x)空值 Azure SQL 数据库和 Azure SQL 托管实例中提供了所有选项,Always-up-to-date 更新策略。 有关功能可用性的详细信息,请参阅列存储索引中的新增功能。 参数 CREATE CLUSTERED COLUMNSTORE INDEX ...
十三、sql server not exists exists : 强调的是是否返回结果集,不要求知道返回什么, 比如: select name from student where sex = 'm' and mark exists(select 1 from grade where ...) ,只要 exists引导的子句有结果集返回,那么exists这个条件就算成立了,大家注意返回的字段始终为1,如果改成“select 2 from...