UNIQUEThe UNIQUE constraint ensures that all values in a column are unique.SQL UNIQUE Constraint on CREATE TABLEThe following SQL creates a UNIQUE constraint on the "ID" column when the "Persons" table is created:SQL Server / Oracle / MS Access:...
CREATE INDEX l_order_dates_idx ON lineitem (l_orderkey, l_receiptdate, l_commitdate, l_shipdate) CREATE UNIQUE INDEX o_datkeyopr_idx ON ORDERS (o_orderdate, o_orderkey, o_custkey, o_orderpriority) 這是針對之前查詢所產生的可能平行計畫:輸出...
VALUES TINYINT Var TO VARBINARY,请参阅 BINARY TOP VARCHAR,请参阅 TEXT TRAILING VarP TRANSACTION VARYING TRANSFORM VIEW TRANSLATE WHEN TRANSLATION WHENEVER TRIM WHERE TRUE WITH UNION WORK UNIQUE Xor UNIQUEIDENTIFIER YEAR UNKNOWN YESNO,请参阅 BIT ...
index_column_name 要加入搜尋作業的索引資料行名稱。 搭配索引參數指定 FORCESEEK,類似於搭配 FORCESEEK 提示使用 INDEX。 但您可以同時指定要搜尋的索引,以及搜尋作業所要考慮的索引資料行,以更有效地控制查詢最佳化工具所使用的存取路徑。 優化工具可能會視需要考慮更多數據行。 例如,如果指定了非叢集索引,除了指定的...
A UNIQUE index creates a constraint such that all values in the index must be distinct. An error occurs if you try to add a new row with a key value that matches an existing row. If you specify a prefix value for a column in a UNIQUE index, the column values must be unique within...
( logical_expression ) ] <column_set_definition> ::= column_set_name XML COLUMN_SET FOR ALL_SPARSE_COLUMNS ::= [ CONSTRAINT constraint_name ] { { PRIMARY KEY | UNIQUE } [ CLUSTERED | NONCLUSTERED ] ( column_name [ ASC | DESC ] [ ,... n ] ) [ WITH FILLFACTOR = fillfactor...
If we want to create indexes for unique values in a column, we use theCREATE UNIQUE INDEXconstraint. For example, -- create unique indexCREATEUNIQUEINDEXcollege_indexONColleges(college_code); Run Code Here, the SQL command creates a unique index namedcollege_indexon theCollegestable using thecol...
Gets the value of the specified column as aSqlString. GetSqlValue(Int32) Returns the data value in the specified column as a SQL Server type. GetSqlValues(Object[]) Fills an array ofObjectthat contains the values for all the columns in the record, expressed as SQL Server types. ...
Array data type in SQL server Array's IN SQL SERVER? ASCII values for extended characters Assign empty string '' if datetime is null Assign EXEC output to Variable Assigning NULL value to column name using Case Statement of where is SQL SERVER 2008 atomic if not exists() and insert or upd...
UNIQUE:唯一,用于保证该字段的值具有唯一性,可以为空。 FOREIGN KEY:外键,用于限制两个表的关系,用于保证该字段的值必须来自于主表的关联列的值,在从表添加外键约束,用于引用主表中某些的值。 约束可应用在列级或表级。列表所有约束均支持,但外键约束没有效果;表级约束可以支持主键、唯一、外键约束。 删除约束 ...