这里,我们看到了Unique Index的一个特性,就是等号操作时执行计划的差异。对Unique Index而言,进行相等查询的结果只有一行值或者没有,所以没必要进行传统的Index Range Scan操作。此处,执行计划中使用的是Index Unique Scan操作,直接精确定位到指定的记录项目,返回rowid记录。 而一般索引在进行等号检索的时候,通常使用的就...
Let’s start today with unique and non unique non clustered indexes on a table without a clustered index, a so-calledheap tablein SQL Server. The following listing shows how to create our test table and populate it with 80.000 records. Each record needs 400 bytes, therefore SQL Server can ...
DROP PROCEDURE IF EXISTS optimization_sql; CREATE PROCEDURE `optimization_sql`(IN n INT) BEGIN -- 声明 i 初始值 DECLARE i INT DEFAULT 1; WHILE (i <= n) DO -- 编写查询的SQL语句 INSERT INTO sql_optimization_test (docNumber, createUser, amount, createDate, detailed) VALUES( CONCAT("docN...
Question:What is between between "unique index vs non-unique index". Which one is faster. The customer using non-unique and sql is getting delay If we change tp non-unique. Is it work ?Answer:Indexes can be unique or non-unique. Unique indexes guarantee that no two rows of a table ha...
The most significant difference between a Unique and a Non-Unique index is of course the simple fact that in one index, all index entries MUST be unique and in the other index there can be duplicates of an index entry. Although an obvious distinction bet
ALTER TABLE 表名 ADD CONSTRAINT 约束名 UNIQUE (列名1, 列名2,…);复制代码 4. UNIQUE 约束也可以用于创建一个唯一索引: CREATE UNIQUE INDEX 索引名 ON 表名(列名);复制代码 需要注意的是,UNIQUE 约束不仅会阻止重复值的插入,还会在表中自动创建一个唯一索引,以提高查询效率。 0 赞 0 踩最新...
In actual fact, there’s really no such thing as a Non-Unique index in Oracle. In order for Oracle to be able to determine the location of any specific index row entry and for Oracle to be able to determine an appropriate “order” for each index row entry, internally, Oracle cove...
SQL语言中建立惟一性索引的命令是()。 A. CREATE INDEX 索引名 ON 基本表名(属性名) B. CREATE INDEX UNIQUE 索引名 ON 基本表名(属性名) C. CREATE UNIQUE INDEX 索引名 ON 基本表名(属性名) D. CREATE DISTINCT INDEX索引名 ON 基本表名(属性名) ...
创建唯一非聚集索引的SQL语句关键字是()。A.unique nonclusteredB.nonclusteredC.create nonclusteredD.以上都不对
百度试题 题目创建唯一索引的SQL语句是( ) A.CREATE UNIQUE INDEXB.CREATE INDEXC.ADD UNIQUE INDEXD.ADD INDEX相关知识点: 试题来源: 解析 A 反馈 收藏