begin for x in 1..1000000 loop insert into T_INDEXTest values(x, 'AA'||x); end loop; commit; end; 1. 2. 3. 4. 5. 6. 7. 8. 9. 4、不同的条件查询效果 -- 创建索引 create index index_test on T_INDEXTEST(name); select * from T_INDEXTEST where id = 765431; -- 慢 sele...
第一步:删除约束,清空数据,写入测试数据 test=#altertabletbl_uniquedropconstraintuk_tbl_unique_a_b ;ALTERTABLEtest=#deletefromtbl_unique ;DELETE3test=#insertintotbl_unique (a,b)values(1,1),(1,1),(1,1);INSERT03test=#insertintotbl_unique (a)values(2),(2),(2);INSERT03test=#select*from...
Key即键值,是关系模型理论中的一部份,比如有主键(Primary Key),外键(Foreign Key)等,用于数据完整性检否与唯一性约束等。 而Index则处于实现层面,比如可以对表的任意列建立索引,那么当建立索引的列处于SQL语句中的Where条件中时,就可以得到快速的数据定位,从而快速检索。 至于Unique Index,则只是属于Index中的一种...
出现此问题的原因是,将UniqueValues查询属性设置为“是”时,会向生成的 SQL 语句添加 DISTINCT 关键字 (keyword) 。 DISTINCT 关键字 (keyword) 指示 Access 执行记录之间的比较。 当 Access 在两个备注字段之间执行比较时,Access 会将这些字段视为具有 255 个字符限制的文本字段。 有时,大于 255 个...
SQL Server / Oracle / MS Access: ALTERTABLEPersons DROPCONSTRAINTUC_Person; Exercise? What does the SQLUNIQUEconstraint ensure? That a column cannot contain NULL values That all values in a column are different That a column must always contain a value ...
You can set the UniqueValues property in the query's property sheet or in SQL view of the Query window. Note: You can set this property when you create a new query by using an SQL statement. The DISTINCT predicate corresponds to the UniqueValues property setting. The DISTINCTROW predicate ...
insert into t (a ,b ) values (null,1); # 不能重复 insert into t (a ,b ) values (null,null);#可以重复 四、使用UNIQUE KEY [sql]view plain copy CREATE TABLE `secure_vulnerability_warning` ( ...
外键约束 foreign key 外键约束的要求： 父表和字表必须使用相同的存储引擎，禁止使用临时表； 数据库...
SQL Server Unique constraint for values in different columnI agree 100% with the above comments ...
Short explanation: The first part (($A$2:$A2=A2)*($B$2:$B2="PA")*($C$2:$C2=0)) checks if the current row matches the [User ID], has "PA" in the [PaymentType], and has a [ReasonCode] of 0. This is your condition for an unsuccessful deposit attempt. ...