[Oracle 学习笔记] 06 DML

DML包括 INSERT   DELETE   UPDATE  

　　SQL> INSERT INTO students VALUES(10138,10101, '王一'，‘20-12 月-1989’)

　　SQL> UPDATE students SET student_id = 10195 WHERE student_id = 15252;

　　SQL> DELETE FROM students_grade;

　　删除数据  TRUNCATE TABLE 截断表  用于删除表中所有的数据

　　SQL> TRUNCATE TABLE teachers

　　DELETE删除的表中所有数据时，不会释放表所占的空间，并且操作可以撤销（ROLLBACK）；TRUNCATE TABLE删除表的所有数据时，执行速度更快，而且还会释放表、段所占用的空间，并且操作不能撤销。

 

　　带子查询的DML

　　SQL> INSERT INTO students_computer (SELECT * FROM students WHERE specialty = '计算机');

　　SQL> UPDATE teachers SET bonus = (SELECT AVG(bonus) FROM teachers) WHERE bonus IS NULL;

　　SQL> DELETE FROM teachers WHERE wage > (SELECT 1.1*AVG(wage) FROM teachers);