Oracle442个应用场景------------基础应用场景

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应用场景178：最简单的select语句

SELECT * FROM Employees;

应用场景179：指定要查询的列

COL EMP_NAME FORMAT A20
COL SEX FORMAT A10
COL TITLE FORMAT A10
SELECT Emp_name, Sex, Title FROM HRMAN.Employees;

应用场景180：使用DISTINCTkeyword

SELECT Title FROM HRMAN.Employees;

SELECT DISTINCT Title FROM HRMAN.Employees;

应用场景181：使用ROWNUM

COL EMP_NAME FORMAT A20
COL SEX FORMAT A10
COL TITLE FORMAT A10
SELECT Emp_name, Sex, Title FROM HRMAN.Employees
WHERE ROWNUM<=3;

应用场景182：改变显示的列标题

COL 姓名 FORMAT A20
COL 性别 FORMAT A4
COL 职务 FORMAT A10
COL 身份证 FORMAT A20
SELECT EMP_NAME AS 姓名, SEX AS 性别, TITLE AS 职务, WAGE AS 工资, IDCARD AS 身份证 FROM HRMAN.Employees;

应用场景183：设置查询条件

COL EMP_NAME FORMAT A20
SELECT Emp_Name, Wage FROM HRMAN.Employees WHERE Wage > 3000 AND Wage < 4000;

应用场景184：在查询条件中使用BITWEEN keyword

COL EMP_NAME FORMAT A20
SELECT Emp_Name, Wage FROM HRMAN.Employees WHERE Wage BETWEEN 3000 AND 4000;

应用场景185：在查询条件中使用IN关键

COL EMP_NAME FORMAT A20
COL TITLE FORMAT A20
SELECT EMP_NAME, TITLE, WAGE FROM HRMAN.Employees WHERE Emp_name IN ('张三', '李四', '王五');

应用场景186：实现模糊查询

COL EMP_NAME FORMAT A20
COL TITLE FORMAT A20
COL IDCard FORMAT A20
SELECT EMP_NAME, TITLE, IDCard FROM HRMAN.Employees
WHERE IDCard LIKE '%ddd%';

COL EMP_NAME FORMAT A20
COL TITLE FORMAT A20
COL IDCard FORMAT A20
SELECT EMP_NAME, TITLE, IDCard FROM HRMAN.Employees
WHERE IDCard LIKE '110123_adx_';

应用场景187：排序结果集

COL EMP_NAME FORMAT A20
COL TITLE FORMAT A20
COL IDCard FORMAT A20
SELECT EMP_NAME, TITLE, IDCard FROM HRMAN.Employees
ORDER BY Emp_name;

COL EMP_NAME FORMAT A20
COL TITLE FORMAT A20
SELECT EMP_NAME, TITLE, Wage FROM HRMAN.Employees
ORDER BY Wage DESC;

应用场景188：对多列进行排序

COL EMP_NAME FORMAT A20
COL SEX FORMAT A20
SELECT EMP_NAME, Sex, Wage FROM HRMAN.Employees
ORDER BY Sex, Wage;

应用场景189：使用分组统计

COL 职务 FORMAT A10
SELECT Title AS 职务, AVG(Wage) AS 平均公资 FROM HRMAN.Employees GROUP BY Title;

COL Sex FORMAT A10
COL Title FORMAT A10
SELECT Sex, Title, AVG(Wage) FROM HRMAN.Employees GROUP BY Title;

SELECT Dep_Id, AVG(Wage) FROM HRMAN.Employees
GROUP BY Dep_Id HAVING AVG(Wage) > 4000;

应用场景190：连接查询

内连接
COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT  t1.Dep_name, t2.Emp_name FROM HRMAN.Departments t1, HRMAN.Employees t2
WHERE t1.Dep_id=t2.Dep_id;

外链接：
COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT  t1.Dep_name, t2.Emp_name FROM HRMAN.Departments t1 INNER JOIN HRMAN.Employees t2
ON t1.Dep_id=t2.Dep_id;

COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT  t1.Dep_name, t2.Emp_name FROM HRMAN.Departments t1 LEFT JOIN HRMAN.Employees t2
ON t1.Dep_id=t2.Dep_id;

COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT  t1.Dep_name, t2.Emp_name FROM HRMAN.Employees t2 RIGHT JOIN HRMAN.Departments t1
ON t1.Dep_id=t2.Dep_id;

COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT  t1.Dep_name, t2.Emp_name FROM HRMAN.Employees t2 FULL JOIN HRMAN.Departments t1
ON t1.Dep_id=t2.Dep_id;

交叉连接
COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT  t1.Dep_name, t2.Emp_name FROM HRMAN.Employees t2 CROSS JOIN HRMAN.Departments t1;

应用场景191：在连接查询中对空值中对空值的推断

COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT  t1.Dep_name, t2.Emp_name FROM HRMAN.Departments t1 LEFT JOIN HRMAN.Employees t2
ON t1.Dep_id=t2.Dep_id;

COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT  t1.Dep_name, t2.Emp_name FROM HRMAN.Departments t1 LEFT JOIN HRMAN.Employees t2
ON t1.Dep_id=t2.Dep_id
WHERE t2.Emp_id IS NULL;

应用场景192：一个简单地子查询

查询办公室的全部员工：
COL Emp_name FORMAT A20
COL Title FORMAT A20
SELECT Emp_Name, Title FROM HRMAN.Employees WHERE Dep_Id =
(SELECT Dep_Id FROM HRMAN.Departments WHERE Dep_name = '办公室');

返回两个部门的值：
COL Emp_name FORMAT A20
COL Title FORMAT A20
SELECT Emp_Name, Title FROM HRMAN.Employees WHERE Dep_Id =
(SELECT Dep_Id FROM HRMAN.Departments WHERE Dep_name = '办公室' OR Dep_name = '人事部');

应用场景193：在查询中使用具和函数返回值

统计表中全部工资低于品级工资的员工的信息

COL Emp_name FORMAT A20
COL Title FORMAT A20
SELECT Emp_name, Title, Wage FROM HRMAN.Employees WHERE Wage <
(SELECT AVG(Wage) FROM HRMAN.Employees);

应用场景194：INkeyword与返回值的子查询

查询办公室和人事部中的员工信息

COL Emp_name FORMAT A20
COL Title FORMAT A20
SELECT Emp_name, Title, Wage FROM HRMAN.Employees WHERE Dep_Id IN
(SELECT Dep_Id FROM HRMAN.Departments WHERE Dep_name = '办公室' OR Dep_name = '人事部');

应用场景195：EXISTSkeyword与子查询

查询人事部中的员工信息
COL Emp_name FORMAT A20
COL Title FORMAT A20
SELECT Emp_name, Title, Wage FROM HRMAN.Employees e
WHERE EXISTS
(SELECT Dep_id FROM HRMAN.Departments d
WHERE e.Dep_id = d.Dep_id AND d.Dep_name='人事部');

使用INkeyword：
COL Emp_name FORMAT A20
COL Title FORMAT A20
SELECT Emp_name, Title, Wage FROM HRMAN.Employees e
WHERE e.Dep_id IN
(SELECT Dep_id FROM HRMAN.Departments d
WHERE e.Dep_id = d.Dep_id AND d.Dep_name='人事部');

应用场景196：使用UNIONkeyword的合并查询

从表中Employee中查询各个部门的部门经理

COL Dep_name FORMAT A20
COL Emp_name FORMAT A20
SELECT Dep_Id, Dep_Name FROM HRMAN.Departments
UNION
SELECT Dep_Id, Emp_Name FROM HRMAN.Employees WHERE Title = '部门经理';

工资大于3000的员工记录：

COL Emp_name FORMAT A20
COL Title FORMAT A20
SELECT Emp_name, Title, Wage FROM HRMAN.Employees
UNION
SELECT Emp_name, Title, Wage FROM HRMAN.Employees WHERE Wage > 3000;

高效率：
COL Emp_name FORMAT A20
COL Title FORMAT A20
SELECT Emp_name, Title, Wage FROM HRMAN.Employees
UNION ALL
SELECT Emp_name, Title, Wage FROM HRMAN.Employees WHERE Wage > 3000;

应用场景197：使用select语句中的DECODE函数

SELECT Emp_name, DECODE(Sex, '男', '先生', '女', '女士', '未知') AS Sex
FROM HRMAN.Employees;

应用场景198：使用select与剧中CASE函数

SELECT Emp_name, CASE Sex WHEN '男' THEN '先生' WHEN '女' THEN '女士' ELSE '未知' END AS Sex
FROM HRMAN.Employees;

查询表Employees中的员工工资级别：

SELECT Emp_name, Wage, CASE WHEN Wage<=3000 THEN '低' WHEN Wage>3000 AND Wage<5000 THEN '中' WHEN Wage>=5000 THEN '高' END AS GRADE
FROM HRMAN.Employees;

应用场景199：保存查询结果

将办公室的全部员工的姓名和职务信息保存到表中OFFICE：

COL Emp_name FORMAT A20
COL Title FORMAT A20
CREATE TABLE HRMAN.Office AS
SELECT e.Emp_Name, e.Title
FROM HRMAN.Employees e, HRMAN.Departments d
WHERE e.Dep_id = d.Dep_Id AND d.Dep_Name = '办公室';
SELECT * FROM HRMAN.Office;

应用场景200：插入数据语句

INSERT INTO HRMAN.Departments VALUES(100, '公关部');
SELECT * FROM HRMAN.Departments;

INSERT INTO HRMAN.Employees (Emp_Name, Sex,Title,  IdCard, Dep_Id)
VALUES ('小明', '男', '职员', '110123456789', 2);

应用场景201：在插入数据时利用默认值

ALTER TABLE HRMAN.Employees ADD InputDate date DEFAULT(sysdate);

INSERT INTO HRMAN.Employees (Emp_Name, Sex,Title,  IdCard, Wage, Dep_Id)
VALUES ('小李', '男', '职员', '210123456789', 2500, 2);

应用场景202：改动数据语句

将表中的全部记录工资添加10%：

UPDATE HRMAN.Employees SET Wage=Wage*1.1;

将表中全部部门为"办公室"的员工工资添加10%

UPDATE HRMAN.Employees SET Wage=Wage*1.1
WHERE Dep_id = (SELECT Dep_id FROM HRMAN.Departments WHERE Dep_name = '办公室');

应用场景203：改动数据时不同意在唯一性约束列中使用同样的值

ALTER TABLE HRMAN.Employees
ADD CONSTRAINT UK_EMPNAME
UNIQUE(Emp_name);

UPDATE HRMAN.Employees SET Emp_name='张三' WHERE Emp_name='李四';

应用场景204：改动数据是不能违反检查约束

ALTER TABLE HRMAN.Employees
ADD CONSTRAINT CK_EMPWAGE CHECK(WAGE>0);

UPDATE HRMAN.Employees SET Wage=-1 WHERE Emp_Name='张三';

应用场景205：改动数据时不能违反外键约束

为表HRMAN。Departments的DEP_id列和表HRMAN.Employees的DEP_ID列中创建外键约束
ALTER TABLE HRMAN.Employees
ADD CONSTRAINT FK_EMP_DEPID
FOREIGN KEY(Dep_id) REFERENCES HRMAN.Departments(Dep_id);

UPDATE HRMAN.Employees SET Dep_id=200 WHERE Emp_Name='张三';

应用场景206：删除数据语句

DELETE FROM HRMAN.Employees WHERE Emp_Name = '小明';

TRUNCATE TABLE HRMAN.Employees;