sql demo
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xiangwb
@@ -36,7 +36,7 @@ LPAD,RPAD补位函数,若补位小于原长度,一律从左往右截
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要求显示指定内容指定位数,若不足则补充若干指定字符以达到要显示的长度
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SELECT ENAME,rPAD(SAL,5,'$') FROM EMP_XWBING;
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SUBSTR截取字符串
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SUBSTR 截取字符串
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截取给定字符串,从指定位置开始截取指定个字符,在数据库中,下标都是从1开始的!!!
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SELECT SUBSTR('think in java',5,3) FROM dual;
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SELECT SUBSTR('think in java',-4,3) FROM dual;
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@@ -54,7 +54,7 @@ SELECT INSTR('think in java','in',2,2)FROM dual;
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SELECT ENAME,SAL,DEPTNO FROM emp_xwbing WHERE LOWER(ENAME)='smith';
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SELECT ename,sal FROM emp_xwbing WHERE LENGTH(ename)=5;
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SELECT ename,sal FROM emp_xwbing WHERE substr(ename,1,1)='A';
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SELECT ename,sal FROM emp_xwbing WHERE SUBSTR(ename,1,1)='A';
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数字函数
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@@ -143,7 +143,7 @@ CREATE TABLE STUDENT_XWBING(ID NUMBER(4),NAME CHAR(20),GENDER CHAR(1));
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INSERT INTO STUDENT_XWBING VALUES(1000,'李莫愁','f');
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insert into student_xwbing values(1001,'林平之',NULL);
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insert into student_xwbing(id,name) values(1002,'张无忌');
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SELECT *FROM student_xwbing;
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SELECT * FROM student_xwbing;
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UPDATE student_xwbing SET gender='m' WHERE gender IS NULL;
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UPDATE student_xwbing SET gender=NULL WHERE gender='m';
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@@ -157,9 +157,10 @@ SELECT ENAME,SAL,COMM FROM EMP_XWBING;
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NVL(P1,P1) 若p1为NULL,函数返回p2. 若不为NULL,函数返回p1自身.所以该函数的作用是将NULL替代换为非NULL值
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查看每个员工的收入?
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SELECT ENAME,SAL,SAL+nvl(BOUNS,0) FROM EMP_XWBING;
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SELECT ENAME,SAL,IFNULL(BOUNS,0) FROM EMP_XWBING;//MYSQL
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SELECT ENAME,SAL,SAL+IFNULL(BOUNS,0) FROM EMP_XWBING;//MYSQL
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NVL2(P1,P2,P3) 若p1不为NULL值为p2,p1为NULL值为p3
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查看每个员工的奖金情况?
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SELECT ENAME,SAL,nvl2(BOUNS,'有奖金','无奖金') FROM EMP_XWBING;
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SELECT ENAME,SAL,NVL2(BOUNS,'有奖金','无奖金') FROM EMP_XWBING;
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IF(ISNULL(p1),p2,p3) 若p1为null
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SELECT ENAME,SAL,IF(ISNULL(BOUNS),'无奖金','有奖金') FROM EMP_XWBING;//MYSQL ISNULL(字段) true返回1
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@@ -1,6 +1,6 @@
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SELECT 子句中 可以对字段加别名,别名前加空格或as,若希望别名区分大小写或者包含空格,可以使用双引号将别名括起来
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SELECT ENAME,SAL*12 SAL FROM EMP_XWBING;
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SELECT ename,sal*12 AS "s al" FROM emp_xwbing;
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SELECT ENAME,SAL*12 SAL FROM EMP_XWBING;
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SELECT ename,sal*12 AS "S al" FROM emp_xwbing;
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查询条件:
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<>不等于
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@@ -8,7 +8,7 @@ SELECT ename,sal FROM emp_xwbing WHERE sal<2000;
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SELECT * FROM emp_xwbing WHERE deptno<>10;
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SELECT * FROM emp_xwbing WHERE hiredate<to_date('1981-1-1','yyyy-mm-dd');
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AND OR 与和或 AND优先级高于or
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AND OR 与和或 AND 优先级高于 OR
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SELECT * FROM emp_xwbing WHERE sal>1000 AND job='CLERK';
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SELECT * FROM emp_xwbing WHERE sal>1000 OR job='CLERK';
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SELECT * FROM emp_xwbing WHERE sal>1000 AND (job='CLERK' OR JOB='SALESMAN');
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@@ -24,16 +24,16 @@ IN(list), NOT IN(list)
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判断是否在列表中,常用在子查询中
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SELECT * FROM EMP_XWBING WHERE JOB IN('CLERK','SALESMAN');
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BETWEEN...AND...之间
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BETWEEN AND 之间
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SELECT sal FROM emp_xwbing WHERE sal BETWEEN 1500 AND 3000;
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IS NULL ,IS NOT NULL
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ANY,ALL 需要配合> >= < <= 一个列表使用,常用于判断子查询的结果
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SELECT * FROM emp_xwbing WHERE sal>all(2800,3000,1800);
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IS NULL,IS NOT NULL
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SELECT * FROM emp_xwbing WHERE comm IS NOT NULL AND sal>1300;
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SELECT * FROM emp_xwbing WHERE hiredate>to_date('1981-1-1','yyyy-mm-dd') AND sal*12>30000;
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ANY,ALL 需要配合> >= < <= 一个列表使用,常用于判断子查询的结果
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SELECT * FROM emp_xwbing WHERE sal>ALL(2800,3000,1800);
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DISTINCT 过滤重复,必须跟在SELECT后面.可以对多列去重,去重原则是这些列的组合没有重复
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SELECT DISTINCT job FROM emp_xwbing;
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@@ -51,49 +51,47 @@ DESC:降序
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SELECT ename ,sal FROM emp_xwbing ORDER BY sal;
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SELECT ename ,sal,deptno FROM emp_xwbing ORDER BY deptno,sal DESC;
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SELECT ename FROM emp_xwbing ORDER BY ename;
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ORDER BY field(字段,'','');//mysql
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SELECT * FROM emp_xwbing ORDER BY field(字段,'','');//mysql
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聚合函数又称多行函数:用来统计结果的
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max,min 统计最大值,最小值
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MAX,MIN 统计最大值,最小值
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查看最高工资?
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SELECT max(sal),min(sal) FROM emp_xwbing;
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SELECT MAX(sal),MIN(sal) FROM emp_xwbing;
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avg,sum 统计平均值与总和
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AVG,SUM 统计平均值与总和
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查看平均工资和工资总和
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SELECT trunc(avg(sal)) avg,sum(sal) sum FROM emp_xwbing;
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SELECT trunc(AVG(sal)) avg,SUM(sal) sum FROM emp_xwbing;
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count 统计的是记录条数,而不关注具体该字段的取值,
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COUNT 统计的是记录条数,而不关注具体该字段的取值,
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统计表中记录数,常使用 COUNT(*)
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查看公司员工人数?
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SELECT count(ename) FROM emp_xwbing;
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统计表中记录数,常使用couont (*)
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SELECT count(*) FROM emp_xwbing;
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SELECT COUNT (*) FROM emp_xwbing;
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所有聚合函数忽略NULL值
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SELECT avg(nvl(comm,0)),sum(comm) FROM emp_xwbing;
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SELECT AVG(nvl(comm,0)),SUM(comm) FROM emp_xwbing;
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分组:
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GROUP BY 子句
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GROUP BY 子句允许将结果集按照给定的字段值相同的额记录看作一组,然后配合聚合函数对每组记录进行统计
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GROUP BY 子句允许将结果集按照给定的字段值相同的记录看作一组,然后配合聚合函数对每组记录进行统计
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查看每个部门的最高工资?
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SELECT deptno FROM emp_xwbing GROUP BY deptno;
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当SELECT中含有聚合函数时,凡不在聚合函数中的单独字段都必须出现在GROUP BY子句中
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SELECT MAX (sal),deptno FROM emp_xwbing GROUP BY deptno;
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当SELECT中含有聚合函数时,凡不在聚合函数中的单独字段都必须出现在 GROUP BY 子句中
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查看每个职位的平均工资和工资总和?
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SELECT avg(sal), sum(sal) FROM emp_xwbing GROUP BY job;
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SELECT AVG(sal), SUM(sal) FROM emp_xwbing GROUP BY job;
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查看每个部门各有多少人?
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SELECT count(ename),deptno FROM emp_xwbing GROUP BY deptno;
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SELECT COUNT(*),deptno FROM emp_xwbing GROUP BY deptno;
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查看每个部门的平均工资,前提是该部门平均工资高于2000?
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SELECT avg(sal),deptno FROM emp_xwbing WHERE avg(sal)>2000 GROUP BY deptno;
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WHERE中不允许使用聚合函数作为过滤条件,原因在于过滤时机不同.WHERE的过滤时机是在第一次从表中检索数据是添加过滤条件,用来确定那些数据可以被查出来,以确定结果集
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HAVING子句:having必须跟在 GROUP BY 子句之后,可以使用聚合函数作为过滤条件.使之可以对分组进行过滤,将满足条件的分组保留,不满足的去掉
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SELECT avg(sal),deptno FROM emp_xwbing GROUP BY deptno having avg(sal)>2000;
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HAVING子句:HAVING必须跟在 GROUP BY 子句之后,可以使用聚合函数作为过滤条件.使之可以对分组进行过滤,将满足条件的分组保留,不满足的去掉
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SELECT AVG(sal),deptno FROM emp_xwbing GROUP BY deptno HAVING AVG(sal)>2000;
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@@ -114,7 +112,7 @@ SELECT e.ename,e.deptno,d.dname FROM emp_xwbing e,dept_xwbing d WHERE e.deptno=d
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SELECT e.ename,d.dname FROM emp_xwbing e,dept_xwbing d WHERE e.deptno=d.deptno AND d.loc='NEW YORK';
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查看平均工资高于2000的部门所在地?
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SELECT avg(e.sal), d.loc ,d.dname FROM emp_xwbing e,dept_xwbing d WHERE e.deptno=d.deptno GROUP BY d.dname,d.loc having avg(e.sal)>2000;
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SELECT AVG(e.sal), d.loc ,d.dname FROM emp_xwbing e,dept_xwbing d WHERE e.deptno=d.deptno GROUP BY d.dname,d.loc HAVING AVG(e.sal)>2000;
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内连接:关联查询的另一种写法
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查看sales部门员工信息?
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@@ -136,7 +134,7 @@ SELECT E.ENAME ,M.ENAME BOSS FROM EMP_XWBING E,EMP_XWBING M WHERE E.MGR=M.EMPN
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JONES的手下?
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SELECT E.ENAME FROM EMP_XWBING E,EMP_XWBING M WHERE E.MGR=M.EMPNO(+) AND m.ename='JONES';
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查看每个领导有几个手下?
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SELECT count(e.mgr),m.ename FROM EMP_XWBING E,EMP_XWBING M WHERE E.MGR=M.EMPNO GROUP BY m.ename;
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SELECT COUNT(e.mgr),m.ename FROM EMP_XWBING E,EMP_XWBING M WHERE E.MGR=M.EMPNO GROUP BY m.ename;
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查看JONES的上司在哪个城市?
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SELECT d.loc FROM EMP_XWBING E,EMP_XWBING M , dept_xwbing d WHERE E.MGR=M.EMPNO AND m.deptno=d.deptno AND e.ename='JONES' ;
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@@ -29,20 +29,20 @@ SELECT * FROM EMP_XWBING;
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多行单列:常用在WHERE中(配合 IN,ANY,ALL)
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多行多列:常用在WHERE中作为表看待
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查看比clerk和salesman部门工资都高的额员工?
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查看比clerk和salesman部门工资都高的员工?
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SELECT ename,sal FROM emp_xwbing WHERE sal>ALL(SELECT deptno FROM emp_xwbing WHERE job='SALESMAN' OR job='CLERK');
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查看和clerk相同部门的其他职位员工?
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SELECT ename FROM emp_xwbing WHERE deptno in (SELECT deptno FROM emp_xwbing WHERE JOB='CLERK');
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EXISTS 关键字
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用在WHERE中,其后要根一个子查询,作用是若子查询至少可以查询出一条记录,那么exisets表达式返回真,NOT EXISTS则起到相反的作用,查不到数据则返回真
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用在WHERE中,其后要根一个子查询,作用是若子查询至少可以查询出一条记录,那么exisets表达式返回真,NOT EXISTS 则起到相反的作用,查不到数据则返回真
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产看有员工的部门?
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SELECT d.deptno,d.dname,d.loc FROM dept_xwbing d WHERE EXISTS(SELECT *FROM EMP_XWBING e WHERE e.deptno=d.deptno);
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没有下属的员工?
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SELECT n.ENAME FROM EMP_XWBING n WHERE NOT EXISTS(SELECT *FROM EMP_XWBING m WHERE N.EMPNO=M.MGR);
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查询列出最低薪水高于部门30的最低薪水的部门的最低薪水?
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SELECT min(sal),deptno FROM emp_xwbing GROUP BY deptno having min(sal)>(SELECT min(sal) FROM emp_xwbing WHERE deptno=30 );
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SELECT min(sal),deptno FROM emp_xwbing GROUP BY deptno having min(sal)>(SELECT min(sal) FROM emp_xwbing WHERE deptno=30);
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子查询在FROM部分:
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查看高于自己所在部门平均工资的员工信息?
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@@ -1,4 +1,4 @@
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CREATE OR REPLACE VIEW V_EMP_10_XWBING AS SELECT empno id,ename,sal*12 salary ,deptno FROM EMP_XWBING WHERE deptno=10 WITH READ ONLY;
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CREATE OR REPLACE VIEW V_EMP_10_XWBING AS SELECT empno id,ename,sal*12 salary ,deptno FROM EMP_XWBING WHERE deptno=10 WITH READ ONLY;
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CREATE OR REPLACE VIEW V_EMP_10_XWBING AS SELECT empno id,ename,sal*12 salary ,deptno FROM EMP_XWBING WHERE deptno=10 WITH CHECK OPTION;
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视图:
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数据库对象之一
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