ALTER TABLE ADD CONSTRAINT UNIQUE(); 实例2,修改数据表 demo_department,指定部门的名称唯一,输入的 SQL 语句和运行结果如下所示。 mysql> ALTER TABLE demo_department -> ADD CONSTRAINT unique_name UNIQUE(name); Query OK, 0 rows affected (0
慢查询日志概念 MySQL的慢查询日志是MySQL提供的一种日志记录,它用来记录在MySQL中响应时间超过阀值的语句,具体指运行时间超过long_query_time值的SQL,则会被记录到慢查询日志中...默认情况下,Mysql数据库并不启动慢查询日志,需要我们手动来设置这个参数,当然,如果不是调优需要的话,一般不建议启动该参数,因为开启慢查...
你可以使用 SQL 语句 CREATE TABLE 来创建数据表。...实例 以下为创建数据表 kxdang_tbl 实例: root@host# mysql -u root -p Enter password:*** mysql> use RUNOOB; Database...使用PHP脚本创建数据表 你可以使用 PHP 的 mysqli_query() 函数来创建已存在数据库的数据表。 该函数有两个参数,在执行成...
ALTER TABLE <数据表名> ADD CONSTRAINT <唯一约束名> UNIQUE(<列名>); 【实例3】修改学生表student,指定学生的名子唯一,输入的 SQL 语句和运行结果如下所示。 mysql> alter table student add constraint name unique(name); Query OK, 0 rows affected Records: 0 Duplicates: 0 Warnings: 0 mysql> desc s...
Use Transact-SQL Create a unique constraint using Transact-SQL InObject Explorer, connect to an instance of Database Engine. On theStandardbar, selectNew Query. Copy and paste the following example into the query window and selectExecute. The example creates the tableTransactionHistoryArchive4and ...
No compatible source was found for this media. Verification Now, let us list all the indexes that are created on the CUSTOMERS table using the following query − SHOWINDEXFROMCUSTOMERS; As you observe you can find the column names NAME, and AGE along with the ID (PRIMARY KEY) in the li...
A uniqueifier (or uniquifier as reported by SQL Server internal tools) is a 4-byte value used to make each key unique in a clustered index that allow duplicate key values. This uniqueness is required because each clustering key must point to exactly one record, without the uniqueifier a ...
Try the below query DECLARE @Random NVARCHAR(10);--To store 4 digit random number DECLARE @Final NVARCHAR(MAX)--Final unique random number DECLARE @Upper INT; DECLARE @Lower INT This will create a random number between 1 and 9999
Take note of the result of the above SQL query. Proceed with safely deleting one of the duplicated user ids. Run the below queries in order: 1234DELETE FROM cwd_membership WHERE child_user_id = <duplicated_id>; DELETE FROM cwd_user_attribute WHERE user_...
Emptyset(0.00sec)mysql>INSERTINTOtest_primary_key2(id,username)VALUES(007,'zhouxingxing');Query OK,1row affected (0.01sec)mysql>INSERTINTOtest_primary_key2(id,username)VALUES(007,'zhouxingxing007');ERROR1062(23000): Duplicate entry'7'forkey'PRIMARY' --- primary key 主键,标识记录的唯一性...