当然有了,看我如果应用wm_concat来让这个需求变简单,假设我的APP_USER表中有(id,username,password,age)4个字段。查询结果如下 SQL Code /*这里的表名默认区分大小写/ select'createorreplaceviewasselect'||wm_concat(column_name)||'fromAPP_USER'sqlStr fromuser_
SQL Server 高性能写入的一些总结 1.1.1 摘要 在开发过程中,我们不时会遇到系统性能瓶颈问题,而引起这一问题原因可以很多,有可能是代码不够高效、有可能是硬件或网络问题,也有可能是数据库设计的问题。 本篇博文将针对一些常用的数据库性能调休方法进行介绍,而且,为了编写高效的SQL代码,我们需要掌握一些基本代码优化的...
STRING_AGG (col1.name,',')asforeignKeys, STRING_AGG (col2.name,',')asprincipalKeys--col1.name AS foreignKey,--col2.name AS principalKeyFROMsys.foreign_key_columns fkcINNERJOINsys.objects objONobj.object_id=fkc.constraint_object_idINNERJOINsys.tables tab1ONtab1.object_id=fkc.parent_obje...
Identity caching is used to improve INSERT performance on tables with identity columns.Note: Starting with SQL Server 2017 (14.x), to accomplish this at the database level, see the IDENTITY_CACHE option in ALTER DATABASE SCOPED CONFIGURATION.Scope: Global only. 460 Replaces data truncation ...
The Microsoft Search service (MSSearch.exe) maintains the full-text catalogs for SQL Server 7.0 full-text search to search character-based data types such aschar,varchar,textandntext. Columns that you define astextcan have more than 300 KB of data (ntextcan have more than 150 KB of UNICODE...
When a new row is added to the table, SQL Server provides a unique, incremental value for the column. Identity columns are typically used together with PRIMARY KEY constraints to serve as the unique row identifier for the table. The IDENTITY property can be assigned to tinyint, smallint, ...
Aggregating the rowset data by the sort columns. Using the rowset as a source table in the FROM clause of a query, where the sort and join columns match. UNIQUE Specifies that the data file doesn't have duplicate entries. If the actual rows in the data file aren't sorted according to...
Both Oracle and SQL Server enforce uniqueness by creating unique indexes automatically whenever a PRIMARY KEY or UNIQUE constraint is defined. Additionally, primary key columns are defined automatically as NOT NULL. Only one primary key is allowed per table. A SQL Server clustered index is created ...
Histograms in SQL Server are only built for a single column-the first column in the set of key columns of the statistics object. To create the histogram, the Query Optimizer sorts the column values, computes the number of values that match each distinct column value, and then aggregates the...
SQL SERVER storage II 存储这块除了表之外,还有很多话题,比如index, Log file, Backup, Error Log等等。当然还包含分布式存储。 Index 的存储在表存储这块其实已经讨论的差不多了。主要的两块还没细讲,一是索引的选取规则,二是索引的碎片。 索引的选取规则,在查询优化这块已经有所涉及,我们一会儿看看是不失有...