另: UNIQUE Constraints vs UNIQUE Indexes Many database administrators ask about the difference between a UNIQUE constraint and a UNIQUE index. While you may use different Transact-SQL commands to create them (ALTER TABLE…ADD CONSTRAINT for constraints and CREATE UNIQUE INDEX for indexes), they hav...
Theterm key refers only to the columns defined in the integrity constraint.Because the database enforces a unique constraint byimplicitly creating or reusing anindexon the key columns,the term uniquekey is sometimes incorrectly used as a synonym for unique key constraint orunique index. --数据库...
SYS@anqing2(rac2)> selectindex_name,index_type,uniqueness,generated from user_indexes wheretable_name='UT'; no rows selected 结论: 当约束列上没有索引时,在创建unique constraint 时,oracle 会自动创建unique index,并且该索引不能删除,当删除unique constraint 时,unique index 会自动删除。 2.2 测试unique...
Theterm key refers only to the columns defined in the integrity constraint.Because the database enforces a unique constraint byimplicitly creating or reusing anindexon the key columns,the term uniquekey is sometimes incorrectly used as a synonym for unique key constraint orunique index. --数据库...
对于ORA-00001错误,可以通过如下查询:-bash-4.1$ oerr ora100001,00000,"unique constraint (%s.%s) violated"// *Cause: An UPDATE or INSERT statement attempted to insert a duplicate key.// For Trusted Oracle configured in DBMS MAC mode, you may see// this message if a duplicate entry exists ...
public void setIndexID(DBObjectIDid) Set the Index that implements this UniqueConstraint Parameters: id- the ID of the Index isUnique public static boolean isUnique(Columncol) Returns true if the given table is constrained by a UniqueConstraint (including PKConstraint) in its parent table. T...
unique indexes, 10-24 UNIQUE key constraints, 25-8 composite keys, 25-9, 25-11 constraint checking, 25-23 indexes used to enforce, 25-10 maximum number of columns, 25-10 NOT NULL constraints and, 25-11 nulls and, 25-11 size limit of, 25-10 unique keys, 1-57, 1-58...
using CREATE UNIQUE INDEX. Creating unique indexes through a primary key or unique constraint is not guaranteed to create a new index, and the index they create is not guaranteed to be a unique index.It is just that in a unique index, the rowid is not considered "part of the key" and...
Therefore, in our little example, we can’t simply create a single concatenated unique index on both the ID and NAME columns and use it to police a unique constraint on just the ID column. We must either use a unique index on the ID column or use a non-unique index on both the ID...
UNIQUE约束 以下ALTER TABLE语句包含约束,如果在GaussDB(DWS)直接调用会报错:Cannot create index whose evaluation cannot be enforced to remote nodes. 该约束迁移和PRIMARY KEY类似。如果已有PRIMARY KEY/UNIQUE约束,无需迁移,保持原样。 输入 1 2 3 4 5 6 7 8 CREATE TABLE GCC_PLAN.T1033 ( ROLLOUT_PLAN...