oracle alter语句用法
sql>
sql> create table bar ( n number );table created.
sql>
sql> alter table bar add c char(1);table altered.
sql>
sql> drop table bar;table dropped.
sql>
增加一个日期字段
sql>
sql> create table bar ( n number );table created.
sql>
sql> alter table bar add d date;table altered.
sql>
sql> object_type, status
2 from user_objects
3 where object_name = 'shield'
4 /object_type status
------------------- -------
package valid
package body validsql>
sql> drop table bar;table dropped.
sql>
给己有表的增加字段
sql> -- create demo table
sql> create table employee(
2 id varchar2(4 byte) not null,
3 first_name varchar2(10 byte),
4 last_name varchar2(10 byte),
5 start_date date,
6 end_date date,
7 salary number(8,2),
8 city varchar2(10 byte),
9 description varchar2(15 byte)
10 )
11 /table created.

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Adding MySQL users through the PHP web interface can use MySQLi extensions. The steps are as follows: 1. Connect to the MySQL database and use the MySQLi extension. 2. Create a user, use the CREATEUSER statement, and use the PASSWORD() function to encrypt the password. 3. Prevent SQL injection and use the mysqli_real_escape_string() function to process user input. 4. Assign permissions to new users and use the GRANT statement.

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ToavoidcommonmistakeswithstringdatatypesinMySQL,understandstringtypenuances,choosetherighttype,andmanageencodingandcollationsettingseffectively.1)UseCHARforfixed-lengthstrings,VARCHARforvariable-length,andTEXT/BLOBforlargerdata.2)Setcorrectcharacters


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