primary key 有两个作用,一是约束作用(constraint),用来规范一个存储主键和唯一性,但同时也在此key上建立了一个index; unique key 也有两个作用,一是约束作用(constraint),规范数据的唯一性,但同时也在这个key上建立了一个index; foreign key也有两个作用,一是约束作用(constraint),规范数据的引用完整性,但同时...
Primary Key index on NumField column ' to new table idxNew.Name = "NumIndex" idxNew.Columns.Append "NumField" idxNew.PrimaryKey = True idxNew.Unique = True tblNew.Indexes.Append idxNew ' Append an index on Textfield to new table. ' Note the different technique: Specifying index and '...
cmdidPrimaryKey cmdidPrint cmdidPrintDefault cmdidPrintPreview cmdidProjectDependencies cmdidProjectExplorer cmdidProjectReferences cmdidProjectSettings cmdidPropbrsHide cmdidProperties cmdidPropertiesWindow cmdidPropertyPages cmdidPropSheetOrProperties cmdidQryManageIndexes cmdidQueryOpenDesign cmdi...
I am not an InnoDB expert, but AFAIK, large BLOBS are stored off-page and will not be read into the buffer if it is not accessed. Øystein Grøvlen, Senior Principal Software Engineer, MySQL Group, Oracle, Trondheim, Norway Sorry, you can't reply to this topic. It has been closed...
[System.ComponentModel.TypeConverter(typeof(System.Data.PrimaryKeyTypeConverter))] public System.Data.DataColumn[] PrimaryKey { get; set; } 属性值 DataColumn[] 一个DataColumn 对象数组。 属性 TypeConverterAttribute 例外 DataException 该键是外键。 示例 第一个DataGrid示例演示如何返回 中显示的 的主Da...
In today’s blog posting I want to talk about a very important topic in SQL Server that always confuses people when they first work with SQL Server. It is about the difference between thePrimary Key constraintand the Clustered Index.
言论 适用于 另请参阅 指示索引是否表示表的主键。 设置和返回值 设置并返回布尔值。 言论 默认值为 false。 此属性在已追加到集合Index对象上是只读的。 适用于 Index 对象 (ADOX) 另请参阅 PrimaryKey 和唯一属性示例 (VB) Index 对象 (ADOX)
The primary key creates aCLUSTEREDindex on the column(s) by default in many databases. The specific syntax for working with primary keys may vary slightly depending on the SQL dialect you're using (such as MySQL, PostgreSQL, SQL Server, etc.), so always check the specific documentation for...
December 19, 2002 at 9:32 am #444826 1) A primary key can be non-clustered. 2) A unique index will allow one null value. Of course, if the column is set to NOT NULL, it won't. K. Brian Kelley http://www.truthsolutions.com/ ...
The maximum length of columns in a primary key is 900 bytes. Values within the primary key must be unique; duplicates are not allowed. All columns in a primary key must be set to NOT NULL. Creating a primary key also creates a unique clustered index on the included column(s). ...