Explore all SQL constraints with examples and real-world use cases. Learn PRIMARY KEY, FOREIGN KEY, UNIQUE, CHECK, and more.
下面的示例从 CHECK_CONSTRAINTS 和 CONSTRAINT_COLUMN_USAGE 视图中返回列,以便显示与约束以及对其定义约束的列有关的信息。 SQL 复制 USE AdventureWorks; GO SELECT ccu.TABLE_SCHEMA, ccu.TABLE_NAME, ccu.COLUMN_NAME, cc.CONSTRAINT_SCHEMA, cc.CONSTRAINT_NAME, cc.CHECK_CLAUSE FROM INFORMATION_SCHEMA.CHECK...
-- Return the name of unique constraint. SELECT name FROM sys.objects WHERE type = 'UQ' AND OBJECT_NAME(parent_object_id) = N' DocExc'; GO -- Delete the unique constraint. ALTER TABLE dbo.DocExc DROP CONSTRAINT UNQ_ColumnB_DocExc; GO ...
当执行 INSERT 和 UPDATE 语句时,CHECK CONSTRAINTS 和规则具有相同的数据验证功能。 当列上存在规则和一个或多个 CHECK 约束时,将验证所有限制。 不能在 text、ntext 或 image 列上定义 CHECK 约束。 其他约束信息 为约束创建的索引不能用 DROP INDEX 删除;必须用 ALTER TABLE 删除约束。可以用 ALTER INDEX 重...
Check constraints or partition function of source table ALTER TABLE with variable TableName ALTER vs UPDATE when creating a new column with default value. Alternate queries for MERGE Alternative for OR in WHERE clause Alternative for PIVOT Alternative of CURSOR in SQL to improve performance ?
@Autowired("anyline.service") AnylineService service; //查询默认数据源的SSO_USER表结构 Table table = serivce.metadata().table("SSO_USER"); LinkedHashMap<String, Column> columns = table.getColumns(); //表中的列 LinkedHashMap<String, Constraint> constraints = table.getConstraints(); //表中上...
Unique constraints and check constraints provide more information for the optimizer to use to create optimal execution plans. A unique constraint gives the optimizer information about the expected results. A check constraint can be used to determine whether a table or index has to be accessed to ...
classA(Base):__tablename__="a"id:Mapped[int]=mapped_column(primary_key=True)data:Mapped[str]_sentinel=mapped_column(insert_sentinel=True) We then would do our INSERTs, when this column is present, in this fashion: INSERT INTO a (data, _sentinel) VALUES (?, 1), (?, 2), (?, 3...
Unlike Oracle, SQL Server can define only one column-level CHECK constraint per column per CREATE TABLE statement (although each column constraint can have multiple conditions). Converting the DBMS-specific syntax is the fundamental issue in migrating these constraints. Expand table Oracle SQL Server...
*Data for the table `act_ge_bytearray` */ insert into act_ge_bytearray`(`ID_`,`REV_`,`NAME_`,`DEPLOYMENTID_`,`BYTES_`,`GENERATED_`) values ('135006',1,'文件导出申请流程.bpmn20.xml','135005','<?xmlversion=\"1.0\" encoding=\"UTF-8\"?>\n<definitions xmlns=\"http:/...