第6章数据查询

SQL 的基本概念 ,[object Object],[object Object],[object Object],[object Object],[object Object]

数据定义 ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],查询

查询 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

SELECT 语句可以实现 : 选择投影 Table 1 Table 2 Table 1 Table 1 连接

示例表 sno sname ssex sage sdept 06001 张三男 20 IS 07012 李四男 18 CS 06023 郭一女 20 IS 05044 刘六男 21 MA 07001 田七女 18 MA 07020 丁五男 19 CS Student 表

示例表 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],course 表 sno cno score 06001 1 93 06001 2 85 06001 3 77 06023 2 80 06023 3 91 06023 6 79 07012 4 92 07020 4 68 sc 表

1. 单表查询 ,[object Object],[object Object],SELECT [DISTINCT] {*, 目标列表达式 [ 别名 ],...} FROM 表名 ; 基本的 SELECT 语句 :

选择全部列 sno sname ssex sage sdept --------- -------------- ----------- 06001 张三男 18 IS 07012 李四男 18 CS … … … … … 07020 丁五男 19 CS SELECT * FROM student;

选择指定的列 sno sname --------- ------------- 06001 张三 07012 李四 … … 07020 丁五 SELECT sno, sname FROM student

使用函数 SELECT sname, datediff(year,birthday,getdate()) FROM student; sname 无列名 ---------- --------- --------- 张三 29 李四 27 郭一 27 刘六 28 田七 27 丁五 29 ...

使用函数 SELECT sname, datediff(year,birthday,getdate()) AS sage FROM student; sname sage ---------- --------- --------- 张三 29 李四 27 郭一 27 刘六 28 田七 27 丁五 29 ...

使用算术运算符 SELECT sno, cno, score,score+5 FROM sc; sno cno score 无列名 ---------- --------- --------- 06001 1 93 98 06001 2 85 90 06001 3 77 82 06023 2 80 85 06023 3 91 96 06023 6 79 84 ...

定义列的别名 SELECT ename AS name, sal salary FROM emp; NAME SALARY ------------- --------- ... SELECT ename "Name", sal*12 "Annual Salary" FROM emp; Name Annual Salary ------------- ------------- ...

使用字符连接运算符 SELECT sno + sname AS “ 学生” FROM student; 学生 ------------------- 06001 张三 07012 李四 06023 郭一 05044 刘六 07001 田七 07020 丁五 ... SQL Server2000 使用‘ +’ 进行字符连接运算 ORACLE 使用‘ ||’ 进行字符连接运算

使用字符连接运算符 SELECT rtrim( sno ) + sname AS “ 学生” FROM student; 学生 ------------------- 06001 张三 07012 李四 06023 郭一 05044 刘六 07001 田七 07020 丁五 ... SQL Server2000 使用‘ +’ 进行字符连接运算 ORACLE 使用‘ ||’ 进行字符连接运算

使用字符连接运算符 Employee Details ------------------------- KING is a PRESIDENT BLAKE is a MANAGER CLARK is a MANAGER JONES is a MANAGER MARTIN is a SALESMAN ... 14 rows selected. SELECT ename +‘ ‘+ ‘ is a ’ +’ ‘+job AS "Employee Details" FROM emp;

消除重复行 ,[object Object],SELECT sdept FROM student WHERE sdept=‘CS’; sdept --------- CS CS ...

消除重复行 ,[object Object],SELECT DISTINCT sdept FROM student WHERE sdept=‘CS’; sdept --------- CS ...

练习 : ,[object Object],[object Object],[object Object],Select ＊ from orders Select orderid,orderdate from orders

练习 : ,[object Object],Select orderid,orderdate,orderdate+30 from orders Select orderid,orderdate,’ 预计的发货日期’ , orderdate+30 from orders Select orderid,orderdate+30 as 预计的发货日期 from orders

选择表中的若干元组 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

用于查询的条件表达式使用的运算符 NOT, AND, OR 逻辑运算符 IS NULL, IS NOT NULL 空值判断 LIKE, NOT LIKE 字符匹配 IN , NOT IN 确定集合 [NOT] BETWEEN…AND… 确定范围 = 、 > 、 < 、 >= 、 <= 、 <> 、 != 、 !> 、 !< 比较运算符

使用 SELECT 语句实现选择操作 “… 选取出 DEPTNO 为 10 的所有雇员 " EMP EMPNO ENAME JOB ... DEPTNO 7839 KING PRESIDENT 10 7698 BLAKE MANAGER 30 7782 CLARK MANAGER 10 7566 JONES MANAGER 20 ... EMP EMPNO ENAME JOB ... DEPTNO 7839 KING PRESIDENT 10 7782 CLARK MANAGER 10 7934 MILLER CLERK 10

使用 WHERE 子句来选取元组 SELECT [DISTINCT] {*, 目标列表达式 [ 别名 ], ...} FROM 表名 [WHERE 条件表达式 ]; WHERE 短句跟在 FROM 短句的后面 WHERE 短句中可以使用运算符，包括：关系运算符、逻辑运算符及一些特殊的运算符。

使用 WHERE 子句来选取元组 SELECT ename, job, deptno FROM emp WHERE job='CLERK'; ENAME JOB DEPTNO ---------- --------- --------- JAMES CLERK 30 SMITH CLERK 20 ADAMS CLERK 20 MILLER CLERK 10

使用 where 子句示例 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],丁五李四 sname 19 丁五 18 田七 18 李四 sage sname sno

使用比较运算符 SELECT ename, sal, comm FROM emp WHERE sal<=comm; ENAME SAL COMM ---------- --------- --------- MARTIN 1250 1400

使用 BETWEEN 运算符 ENAME SAL ---------- --------- MARTIN 1250 TURNER 1500 WARD 1250 ADAMS 1100 MILLER 1300 SELECT ename, sal FROM emp WHERE sal BETWEEN 1000 AND 1500; Lower limit Higher limit

使用 IN 运算符 SELECT empno, ename, sal, mgr FROM emp WHERE mgr IN (7902, 7566, 7788); EMPNO ENAME SAL MGR --------- ---------- --------- --------- 7902 FORD 3000 7566 7369 SMITH 800 7902 7788 SCOTT 3000 7566 7876 ADAMS 1100 7788

使用 IN 运算符 ,[object Object],[object Object],[object Object],[object Object],… … 男张三男丁五女田七男李四 ssex sname ssex sname

使用 LIKE 运算符 ,[object Object],[object Object],[object Object],[object Object],[object Object],SELECT ename FROM emp WHERE ename LIKE 'S%';

使用 LIKE 运算符 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

使用 LIKE 运算符 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],使用 LIKE 运算符 SELECT ename FROM emp WHERE ename LIKE '_A%'; ENAME ---------- JAMES WARD SELECT ename FROM emp WHERE ename LIKE 'A%' escape ‘;

使用 IS NULL 运算符 ,[object Object],SELECT ename, mgr FROM emp WHERE mgr IS NULL; ENAME MGR ---------- --------- KING

使用 IS NULL 运算符 ,[object Object],[object Object],[object Object],[object Object]

使用 AND 运算符 SELECT empno, ename, job, sal FROM emp WHERE sal>=1100 AND job='CLERK'; EMPNO ENAME JOB SAL --------- ---------- --------- --------- 7876 ADAMS CLERK 1100 7934 MILLER CLERK 1300

使用 OR 运算符 SELECT empno, ename, job, sal FROM emp WHERE sal>=1100 OR job='CLERK'; EMPNO ENAME JOB SAL --------- ---------- --------- --------- 7839 KING PRESIDENT 5000 7698 BLAKE MANAGER 2850 7782 CLARK MANAGER 2450 7566 JONES MANAGER 2975 7654 MARTIN SALESMAN 1250 ...

SELECT ename, job FROM emp WHERE job NOT IN ('CLERK','MANAGER','ANALYST'); ENAME JOB ---------- --------- KING PRESIDENT MARTIN SALESMAN ALLEN SALESMAN TURNER SALESMAN WARD SALESMAN 使用 NOT 运算符

优先顺序：比较运算符最优先，逻辑运算符中 NOT 优先级第一， AND 其次， OR 最后。 ENAME JOB SAL ---------- --------- --------- KING PRESIDENT 5000 MARTIN SALESMAN 1250 ALLEN SALESMAN 1600 TURNER SALESMAN 1500 WARD SALESMAN 1250 SQL> SELECT ename, job, sal FROM emp WHERE job='SALESMAN' OR job='PRESIDENT' AND sal>1500;

可以使用括号来定义优先顺序。 ENAME JOB SAL ---------- --------- --------- KING PRESIDENT 5000 ALLEN SALESMAN 1600 SQL> SELECT ename, job, sal FROM emp WHERE (job='SALESMAN' OR job='PRESIDENT') AND sal>1500;

IN 和 OR 的关系 ,[object Object],[object Object],[object Object]

练习： ,[object Object],[object Object],[object Object],Select ＊ from orders where shippeddate<date() Select * from customers where country=‘UK’

练习： ,[object Object],[object Object],Select productname,unitprice from products where unitprice between 20 and 25 Select productname,unitprice from products where categoryid in (1,2,3)

练习： ,[object Object],[object Object],Select * from customers where customerid like ‘A%’ Select * from customers where customerid like ‘_ _A%’ and country=‘UK’

ORDER BY 短语 ,[object Object],[object Object],[object Object],注意：如果元组中有空值存在，则在升序时，空值排在结果的最后；在降序时，空值排在结果的最前。

ORDER BY 短语 ,[object Object],[object Object],[object Object],92 07012 68 07020 score sno 68 07012 92 07020 score sno

ORDER BY 短语 ,[object Object],[object Object],[object Object],SELECT ename, job, deptno, hiredate FROM emp ORDER BY hiredate; ENAME JOB DEPTNO HIREDATE ---------- --------- --------- --------- SMITH CLERK 20 17-DEC-80 ALLEN SALESMAN 30 20-FEB-81 ...

按降序排列结果 SELECT ename, job, deptno, hiredate FROM emp ORDER BY hiredate DESC; ENAME JOB DEPTNO HIREDATE ---------- --------- --------- --------- ADAMS CLERK 20 12-JAN-83 SCOTT ANALYST 20 09-DEC-82 MILLER CLERK 10 23-JAN-82 JAMES CLERK 30 03-DEC-81 FORD ANALYST 20 03-DEC-81 KING PRESIDENT 10 17-NOV-81 MARTIN SALESMAN 30 28-SEP-81 ...

按结果列的别名排序 SELECT empno, ename, sal*12 annsal FROM emp ORDER BY annsal; EMPNO ENAME ANNSAL --------- ---------- --------- 7369 SMITH 9600 7900 JAMES 11400 7876 ADAMS 13200 7654 MARTIN 15000 7521 WARD 15000 7934 MILLER 15600 7844 TURNER 18000 ...

按多列排序例、显示所有学生的信息，按系排序，同系中按年龄从大到小排序 Select * from student order by sdept,sage desc 在排序时可以指定多列，系统降按照指定列的顺序依次列示结果

按多列排序 SELECT ename, deptno, sal FROM emp ORDER BY deptno, sal DESC; ENAME DEPTNO SAL ---------- --------- --------- KING 10 5000 CLARK 10 2450 MILLER 10 1300 FORD 20 3000 ...

使用集函数 ,[object Object],EMP “ maximum salary in the EMP table” DEPTNO SAL --------- --------- 10 2450 10 5000 10 1300 20 800 20 1100 20 3000 20 3000 20 2975 30 1600 30 2850 30 1250 30 950 30 1500 30 1250 MAX(SAL) --------- 5000

使用集函数 SELECT 目标列表达式 , 集函数 ( 列名 ) FROM 表名 [WHERE 条件表达式 ] [ORDER BY 列名 ]; ,[object Object],[object Object]

AVG 和 SUM 适用于数值型数据 AVG(SAL) MAX(SAL) MIN(SAL) SUM(SAL) -------- --------- --------- --------- 1400 1600 1250 5600 SELECT AVG(sal), MAX(sal), MIN(sal), SUM(sal) FROM emp WHERE job LIKE 'SALES%';

MIN 和 MAX 适用于不同类型的数据 SELECT MIN(hiredate), MAX(hiredate) FROM emp ; MIN(HIRED MAX(HIRED --------- --------- 17-DEC-80 12-JAN-83

COUNT 函数用于计数 COUNT(*) --------- 6 SELECT COUNT(*) FROM emp WHERE deptno = 30; SELECT COUNT(comm) FROM emp WHERE deptno = 30; COUNT(COMM) ----------- 4 忽略 NULL 值

示例 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],6 COUNT(*) 4 COUNT(DISTINCT sno) 80 AVG(score) 92 MAX(score)

创建数据分组 ,[object Object]

创建数据分组 EMP “ EMP 表中每一部门的平均工资” DEPTNO SAL --------- --------- 10 2450 10 5000 10 1300 20 800 20 1100 20 3000 20 3000 20 2975 30 1600 30 2850 30 1250 30 950 30 1500 30 1250 DEPTNO AVG(SAL) ------- --------- 10 2916.6667 20 2175 30 1566.6667 2916.6667 2175 1566.6667

GROUP BY 短语 SELECT 目标列表达式 , 集函数 ( 列名 ) FROM 表名 [WHERE 条件表达式 ] [GROUP BY 分组条件表达式 ] [ORDER BY 列名 ]; ,[object Object]

使用 GROUP BY 短语 ,[object Object],SELECT AVG(sal) FROM emp GROUP BY deptno; AVG(SAL) --------- 2916.6667 2175 1566.6667

使用 GROUP BY 短语 ,[object Object],SELECT deptno, AVG(sal) FROM emp GROUP BY deptno; DEPTNO AVG(SAL) --------- --------- 10 2916.6667 20 2175 30 1566.6667

SELECT deptno, job, sum(sal) FROM emp GROUP BY deptno, job; DEPTNO JOB SUM(SAL) --------- --------- --------- 10 CLERK 1300 10 MANAGER 2450 10 PRESIDENT 5000 20 ANALYST 6000 20 CLERK 1900 ... 9 rows selected. 按多列分组

按多列分组 EMP “ EMP 表中不同部门不同职位的工资总和” DEPTNO JOB SAL --------- --------- --------- 10 MANAGER 2450 10 PRESIDENT 5000 10 CLERK 1300 20 CLERK 800 20 CLERK 1100 20 ANALYST 3000 20 ANALYST 3000 20 MANAGER 2975 30 SALESMAN 1600 30 MANAGER 2850 30 SALESMAN 1250 30 CLERK 950 30 SALESMAN 1500 30 SALESMAN 1250 JOB SUM(SAL) --------- --------- CLERK 1300 MANAGER 2450 PRESIDENT 5000 ANALYST 6000 CLERK 1900 MANAGER 2975 CLERK 950 MANAGER 2850 SALESMAN 5600 DEPTNO -------- 10 10 10 20 20 20 30 30 30

示例 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],2 2 2 3 2 4 1 1 1 6 COUNT(sno) cno cno

对分组的结果进行筛选 “ 每一部门最高工资大于 $2900” EMP DEPTNO SAL --------- --------- 10 2450 10 5000 10 1300 20 800 20 1100 20 3000 20 3000 20 2975 30 1600 30 2850 30 1250 30 950 30 1500 30 1250 DEPTNO MAX(SAL) --------- --------- 10 5000 20 3000 5000 3000 2850

HAVING 短语 ,[object Object],[object Object],[object Object],SELECT 目标列表达式 , 集函数 FROM 表名 [WHERE 条件表达式 ] [GROUP BY 分组条件表达式 ] [HAVING 条件表达式 ] [ORDER BY 列名 ];

使用 HAVING 短语 SELECT deptno, max(sal) FROM emp GROUP BY deptno HAVING max(sal)>2900; DEPTNO MAX(SAL) --------- --------- 10 5000 20 3000

使用 HAVING 短语 SELECT job, SUM(sal) PAYROLL FROM emp WHERE job NOT LIKE 'SALES%' GROUP BY job HAVING SUM(sal)>5000 ORDER BY SUM(sal); JOB PAYROLL --------- --------- ANALYST 6000 MANAGER 8275

嵌套的集函数 SELECT max(avg(sal)) 2 FROM emp 3 GROUP BY deptno; MAX(AVG(SAL)) ------------- 2916.6667

练习： ,[object Object],[object Object],Select * from orders where customerid like ‘A%’ and year(orderdate)=1996 order by orderid Select supplierid,avg(unitprice) from products group by supllierid

WHERE 和 HAVING ,[object Object],[object Object],[object Object]

2. 嵌套查询 ,[object Object],[object Object],[object Object]

嵌套查询 ,[object Object],[object Object],[object Object],[object Object],[object Object]

嵌套分类 ,[object Object],[object Object],[object Object],[object Object]

带有 IN 谓词的子查询 ,[object Object],[object Object],[object Object],[object Object],[object Object]

多层嵌套 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

带有比较运算符的子查询 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

使用嵌套解决问题 ,[object Object],“ 哪一个雇员的工资比 Jones 高 ?” 主查询 ? “ Jones 的工资是多少 ?” ? 子查询

嵌套查询的实现 SELECT ename FROM emp WHERE sal > (SELECT sal FROM emp WHERE empno=7566); ENAME ---------- KING FORD SCOTT 2975

嵌套查询的实现 ENAME JOB ---------- --------- MILLER CLERK SELECT ename, job FROM emp WHERE job = (SELECT job FROM emp WHERE empno = 7369) AND sal > (SELECT sal FROM emp WHERE empno = 7876); CLERK 1100

HAVING 短语中使用嵌套查询 SELECT deptno, MIN(sal) FROM emp GROUP BY deptno HAVING MIN(sal) > (SELECT MIN(sal) FROM emp WHERE deptno = 20); DEPTNO MIN(SAL) ---------- ---------- 10 1300 30 950 800

以下两个查询结果一样吗 ? SELECT ename, deptno, sal, comm FROM emp WHERE (sal, comm) IN (SELECT sal, comm FROM emp WHERE deptno = 30); SELECT ename, deptno, sal, comm FROM emp WHERE sal IN (SELECT sal FROM emp WHERE deptno = 30) AND comm IN (SELECT comm FROM emp WHERE deptno = 30);

带有 ANY 或 ALL 的子查询 ,[object Object],大于等于 ( 小于等于 ) 子查询中的所有值 >=(<=)ALL 等于 ( 不等于 ) 子查询中的所有值 =(!=)ALL 大于 ( 小于 ) 子查询中的所有值 >(<)ALL 等于 ( 不等于 ) 子查询中某个值 =(!=)ANY 大于等于 ( 小于等于 ) 子查询中某个值 >=(<=)ANY 大于 ( 小于 ) 子查询中某个值 >(<)ANY

示例 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],<all 小于子查询结果中的所有值 <any 小于子查询结果中的某个值 >= MAX >MAX <= MIN <MIN NOT IN ALL >= MIN >MIN <= MAX <MAX IN ANY >= > <= < <> =

使用 ANY 运算符 EMPNO ENAME JOB --------- ---------- --------- 7654 MARTIN SALESMAN 7521 WARD SALESMAN SELECT empno, ename, job FROM emp WHERE sal < ANY (SELECT sal FROM emp WHERE job = 'CLERK') AND job <> 'CLERK'; 950 800 1100 1300

使用 ALL 运算符 EMPNO ENAME JOB --------- ---------- --------- 7839 KING PRESIDENT 7566 JONES MANAGER 7902 FORD ANALYST 7788 SCOTT ANALYST SQL> SELECT empno, ename, job FROM emp WHERE sal > ALL (SELECT avg(sal) FROM emp GROUP BY deptno); 2916.6667 2175 1566.6667

练习 : ,[object Object],select productid,quantity from "order details" where productid in (Select productid from products where unitprice<10)

练习 : ,[object Object],select productid,quantity from "order details" where unitprice <all (Select unitprice from products where categoryid=2)

带有 EXISTS 谓词的子查询 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object]

EXISTS 短语 ,[object Object],[object Object],[object Object],[object Object],[object Object],注：带 exists 的子查询不返回任何数据，只产生逻辑真或逻辑假。

EXISTS 短语 ,[object Object],select productid,quantity from "order details“ where exists (Select productid from products where productid="order details".productid and unitprice<10)

4. 集合查询 ,[object Object],[object Object],[object Object],[object Object]

集合查询 (2) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

3. 多表查询 ,[object Object],[object Object],[object Object],[object Object],[object Object]

连接查询 ( 涉及多个表的查询 ) EMPNO DEPTNO LOC ----- ------- -------- 7839 10 NEW YORK 7698 30 CHICAGO 7782 10 NEW YORK 7566 20 DALLAS 7654 30 CHICAGO 7499 30 CHICAGO ... 14 rows selected. EMP DEPT EMPNO ENAME ... DEPTNO ------ ----- ... ------ 7839 KING ... 10 7698 BLAKE ... 30 ... 7934 MILLER ... 10 DEPTNO DNAME LOC ------ ---------- -------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON

用 SELECT 语句实现连接操作 ,[object Object],[object Object],[object Object],SELECT 表名 1. 目标列 , 表名 2. 目标列 FROM 表名 1, 表名 2 WHERE 表名 1. 列 < 比较运算符 > 表名 2. 列 ; WHERE 表名 1. 列 <BETWEEN> 表名 2. 列 AND 表名 3. 列 ;

等值连接 ,[object Object],[object Object],[object Object]

等值连接 EMP DEPT EMPNO ENAME DEPTNO ------ ------- ------- 7839 KING 10 7698 BLAKE 30 7782 CLARK 10 7566 JONES 20 7654 MARTIN 30 7499 ALLEN 30 7844 TURNER 30 7900 JAMES 30 7521 WARD 30 7902 FORD 20 7369 SMITH 20 ... 14 rows selected. DEPTNO DNAME LOC ------- ---------- -------- 10 ACCOUNTING NEW YORK 30 SALES CHICAGO 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 20 RESEARCH DALLAS 20 RESEARCH DALLAS ... 14 rows selected. Foreign key Primary key

等值连接的实现 SELECT emp.empno, emp.ename, emp.deptno, dept.deptno, dept.loc FROM emp, dept WHERE emp.deptno=dept.deptno; EMPNO ENAME DEPTNO DEPTNO LOC ----- ------ ------ ------ --------- 7839 KING 10 10 NEW YORK 7698 BLAKE 30 30 CHICAGO 7782 CLARK 10 10 NEW YORK 7566 JONES 20 20 DALLAS ... 14 rows selected.

使用表的别名简化工作 SELECT emp.empno, emp.ename, emp.deptno, dept.deptno, dept.loc FROM emp, dept WHERE emp.deptno=dept.deptno; SELECT e.empno, e.ename, e.deptno, d.deptno, d.loc FROM emp e, dept d WHERE e.deptno=d.deptno;

非等值连接 EMP SALGRADE EMPNO ENAME SAL ------ ------- ------ 7839 KING 5000 7698 BLAKE 2850 7782 CLARK 2450 7566 JONES 2975 7654 MARTIN 1250 7499 ALLEN 1600 7844 TURNER 1500 7900 JAMES 950 ... 14 rows selected. GRADE LOSAL HISAL ----- ----- ------ 1 700 1200 2 1201 1400 3 1401 2000 4 2001 3000 5 3001 9999 “ EMP 表中的工资数额在 SALGRADE 表的 LOSAL 和 HISAL 之间”

非等值连接的实现 ENAME SAL GRADE ---------- --------- --------- JAMES 950 1 SMITH 800 1 ADAMS 1100 1 ... 14 rows selected. SELECT e.ename, e.sal, s.grade FROM emp e, salgrade s WHERE e.sal BETWEEN s.losal AND s.hisal;

笛卡尔积： ENAME DNAME ------ ---------- KING ACCOUNTING BLAKE ACCOUNTING ... KING RESEARCH BLAKE RESEARCH ... 56 rows selected. EMP (14 rows) EMPNO ENAME ... DEPTNO ------ ----- ... ------ 7839 KING ... 10 7698 BLAKE ... 30 ... 7934 MILLER ... 10 WHERE 短句省略或无效时，表与表进行笛卡尔积运算。 DEPT (4 rows) DEPTNO DNAME LOC ------ ---------- -------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON “ Cartesian product: 14*4=56 rows”

自身连接 ,[object Object],[object Object],[object Object],[object Object],[object Object],5 3 5 2 6 2 1 second.cpno first.cno

自身连接 EMP (WORKER) EMP (MANAGER) EMPNO ENAME MGR ----- ------ ---- 7839 KING 7698 BLAKE 7839 7782 CLARK 7839 7566 JONES 7839 7654 MARTIN 7698 7499 ALLEN 7698 EMPNO ENAME ----- -------- 7839 KING 7839 KING 7839 KING 7698 BLAKE 7698 BLAKE “ 表中的雇员之间存在上下级关系 "

自身连接的实现 WORKER.ENAME||'WORKSFOR'||MANAG ------------------------------- BLAKE works for KING CLARK works for KING JONES works for KING MARTIN works for BLAKE ... 13 rows selected. SELECT worker.ename+' works for ‘+manager.ename FROM emp worker, emp manager WHERE worker.mgr = manager.empno;

两个以上的表的连接 NAME CUSTID ----------- ------ JOCKSPORTS 100 TKB SPORT SHOP 101 VOLLYRITE 102 JUST TENNIS 103 K+T SPORTS 105 SHAPE UP 106 WOMENS SPORTS 107 ... ... 9 rows selected. CUSTOMER CUSTID ORDID ------- ------- 101 610 102 611 104 612 106 601 102 602 106 604 106 605 ... 21 rows selected. ORD ORDID ITEMID ------ ------- 610 3 611 1 612 1 601 1 602 1 ... 64 rows selected. ITEM

外连接 ,[object Object],[object Object]

外连接 EMP DEPT ENAME DEPTNO ----- ------ KING 10 BLAKE 30 CLARK 10 JONES 20 ... DEPTNO DNAME ------ ---------- 10 ACCOUNTING 30 SALES 10 ACCOUNTING 20 RESEARCH ... 40 OPERATIONS 没有雇员在 OPERATIONS 部门

SQL Server 中的外连接 ,[object Object],[object Object],[object Object],[object Object],SELECT 表名 1. 目标列 , 表名 2. 目标列 FROM 表 1 <left outer join /right outer join /full outer join> 表 2 ON 表名 1. 列 = 表名 2. 列 ;

示例关系 Loan: 关系 Borrow: Perryridge Redwood Downtown Bname 1700 4000 3000 amount L-230 Smith L-230 L-155 Mary L-260 L-170 Jones L-170 Loanno custna Loanno

示例 Loan inner join Borrow on Loan.Loanno=Borrow.Loanno Redwood Downtown Bname 4000 3000 amount L-230 Smith L-230 L-170 Jones L-170 Loanno custna Loanno

示例 Loan natural inner join Borrow on Loan.Loanno=Borrow.Loanno Redwood Downtown Bname 4000 3000 amount Smith L-230 Jones L-170 custna Loanno

示例 Loan left outer join Borrow on Loan.Loanno=Borrow.Loanno NULL NULL 1700 Perryridge L-260 L-230 Smith 4000 Redwood L-230 Downtown Bname 3000 amount L-170 Jones L-170 Loanno custna Loanno

示例 Loan natural right outer join Borrow on Loan.Loanno=Borrow.Loanno Mary NULL NULL L-155 Smith 4000 Redwood L-230 Downtown Bname 3000 amount Jones L-170 custna Loanno

示例 Loan full outer join Borrow on Loan.Loanno=Borrow.Loanno NULL 1700 Perryridge L-260 Mary NULL NULL L-155 Smith 4000 Redwood L-230 Downtown Bname 3000 amount Jones L-170 custna Loanno

复合条件连接 ,[object Object],[object Object],[object Object],[object Object],[object Object]

复合条件连接 ,[object Object],[object Object],[object Object],[object Object]

练习： ,[object Object],Select categories.*,products.* from categories,products where categories.categoryid=products.categoryid

练习： ,[object Object],Select orders.customerid, companyname,orderid,orderdate from customers,orders where customers.customerid=orders.customerid and orders.customerid like “A%”

练习： ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

练习： ,[object Object],select orders.orderid,customers.companyname from orders,customers where orders.customerid=customers.customerid 或： select orders.orderid,customers.companyname from orders inner join customers on orders.customerid=customers.customerid

连接查询 (8) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

第6章数据查询

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