CH-15 SIMPLE QUERY AND GROUPING

Transcription

1 SQL SELECT STATEMENT. ASHOK GARG CH-15 SIMPLE QUERY AND GROUPING The SELECT statement is used to retrieve information from a table. Syntax: SELECT <column-list> FROM <table-name> [WHERE <condition>] [GROUP BY <column-name(s)>] [HAVING <condition>] [ORDER BY <expression>] [ ] optional < > must A table can have all the clause or few clauses, but the order of evolution will remain the same as described in the syntax. 1. Show the detail of EMP table. SQL> SELECT * FROM EMP; EMPNO JOB MGR HIREDATE SAL COMM DEPTNO SMITH CLERK DEC ALLEN SALESMAN FEB WARD SALESMAN FEB JONES MANAGER APR MARTIN SALESMAN SEP BLAKE MANAGER MAY CLARK MANAGER JUN SCOTT ANALYST APR KING PRESIDENT 17-NOV TURNER SALESMAN SEP ADAMS CLERK MAY JAMES CLERK DEC FORD ANALYST DEC MILLER CLERK JAN rows selected. 2. Show the employee no and name. SQL> SELECT EMPNO, FROM EMP; EMPNO

2 7369 SMITH 7499 ALLEN 7521 WARD 7566 JONES 7654 MARTIN 7698 BLAKE 7782 CLARK 7788 SCOTT 7839 KING 7844 TURNER 7876 ADAMS 7900 JAMES 7902 FORD 7934 MILLER 14 rows selected. 3. Show employee no, dept no and salary. SQL> SELECT EMPNO, DEPTNO, SAL FROM EMP; EMPNO DEPTNO SAL rows selected. Above command shows that order of column is not important. NOTE: We can give the entire command in one line or in separate lines, or one word per line. WHERE clause: The WHERE clause is used along with SELECT statement to specify the condition, based on which the rows will be extracted from a table with SELECT. When a WHERE clause is present, the database program goes through the entire table one row at a time and examines each row to determine if the condition is true with the row. 2

3 Operators used to specify the conditions: Relational Operators = Equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to <>,!=, ^= Not equal to Special Operators AND OR NOT Logical Operators Logical AND Logical OR Logical NOT IN BETWEEN LIKE Checking a value in a set Checking a value with in a range. Both the values included in the range. Matching a pattern from a column % One or more or no character _ One and only one character EXAMPLES: 13. Show the details of employees belonging to the department 10. SQL>SELECT * FROM EMP WHERE DEPTNO=10; EMPNO JOB MGR HIREDATE SAL COMM DEPTNO CLARK MANAGER JUN KING PRESIDENT 17-NOV MILLER CLERK JAN List the name and salary of the employees whose salary is more than SQL> SELECT, SAL FROM EMP WHERE SAL>2900; SAL JONES 4284 CLARK 3528 SCOTT 4320 KING 7200 FORD List the employee no and name of Managers. SQL> SELECT EMPNO, FROM EMP WHERE JOB='MANAGER'; 3

4 EMPNO JONES 7698 BLAKE 7782 CLARK 16. List the name of clerks working in department no 30. SQL> SELECT FROM EMP WHERE JOB='CLERK' AND DEPTNO=30; JAMES 17. List the name of clerks and managers. SQL> SELECT FROM EMP WHERE JOB='CLERK' OR JOB='MANAGER'; SMITH JONES BLAKE CLARK ADAMS JAMES MILLER 7 rows selected. 18. List the name of the employees who are not SALESMAN. SQL> SELECT FROM EMP WHERE JOB<>'SALESMAN'; SMITH JONES BLAKE CLARK SCOTT KING ADAMS JAMES FORD MILLER 10 rows selected. 4

5 19. List the details of the employees who joined before the end of October 81. SQL> SELECT * FROM EMP WHERE HIREDATE<'31-OCT-81'; EMPNO JOB MGR HIREDATE SAL COMM DEPTNO SMITH CLERK DEC ALLEN SALESMAN FEB WARD SALESMAN FEB JONES MANAGER APR MARTIN SALESMAN SEP BLAKE MANAGER MAY CLARK MANAGER JUN TURNER SALESMAN SEP Note: The special operator IN and BETWEEN can be used in place of complex relational logical operator. 8. List the employee name whose employee numbers are 7521, 7369, 7839,7934 SQL> SELECT FROM EMP WHERE EMPNO=7521 OR EMPNO=7369 OR EMPNO=7839 OR EMPNO=7934; The above query can be written using the IN operator as follows. SQL> SELECT FROM EMP WHERE EMPNO IN(7521, 7369, 7839,7934); MILLER KING SMITH WARD 9. List the employee details not belonging to department 10, 30 and 40 SQL> SELECT * FROM EMP WHERE DEPTNO NOT IN(10,30,40); EMPNO JOB MGR HIREDATE SAL COMM DEPTNO SMITH CLERK DEC JONES MANAGER APR SCOTT ANALYST APR ADAMS CLERK MAY FORD ANALYST DEC BETWEEN operator is used to specify a range of values. 10 List the employee name and salary, whose salary is between 2000 and SQL> SELECT, SAL FROM EMP WHERE SAL BETWEEN 2000 AND 3000; SAL

6 BLAKE 2850 DISTINCT Clause DISTINCT clause is used to remove duplicate values from a column. List the different jobs available in EMP table. SQL> SELECT DISTINCT JOB FROM EMP; JOB ANALYST CLERK MANAGER PRESIDENT SALESMAN NULL values: NULL values are not a 0 or a blank. It is an unknown or inapplicable value. It can not be compared using the relational or logical operators. The special operator IS is used with the keyword NULL to locate NULL values. 1. List the employee names who are not eligible for commission. SQL> SELECT FROM EMP WHERE COMM IS NULL; SMITH JONES BLAKE CLARK SCOTT KING ADAMS JAMES FORD MILLER 2. List the name and designation of the employee who is not reporting to any one. SQL> SELECT, JOB FROM EMP WHERE MGR IS NULL; JOB

7 KING PRESIDENT 3. List the employees who are eligible for commission. SQL> SELECT FROM EMP WHERE COMM IS NOT NULL; ALLEN WARD MARTIN TURNER 4. List the detail of the employees whose salary is more than 2500 and commission is NULL. SQL> SELECT * FROM EMP WHERE SAL>2500 AND COMM IS NULL; EMPNO JOB MGR HIREDATE SAL COMM DEPTNO JONES MANAGER APR BLAKE MANAGER MAY CLARK MANAGER JUN SCOTT ANALYST APR KING PRESIDENT 17-NOV FORD ANALYST DEC LIKE Operator: The LIKE operator is used with CHAR and VARCHAR2 to match a pattern. % represent a sequence of zero or more characters and _ represents a single character. 1. List the employees whose names start with an S. SQL> SELECT FROM EMP WHERE LIKE 'S%'; SMITH SCOTT 2. List the employee names whose name ends with S. SQL> SELECT FROM EMP WHERE LIKE '%S'; JONES ADAMS JAMES 7

8 3. List the employee names whose names have exactly 4 characters. SQL> SELECT FROM EMP WHERE LIKE ' '; WARD KING FORD 4. List the employee names having I as the second character. SQL> SELECT FROM EMP WHERE LIKE '_I%'; KING MILLER 5. List the employee names who have either LL or TT in their names. SQL> SELECT FROM EMP WHERE LIKE '%LL%' OR LIKE '%TT%'; ALLEN SCOTT MILLER ARITHMETIC COMPUTATIONS WITH COLUMNS: Arithmetic computation can be done on numeric columns. Alias names can be given to column or expressions on query outputs. They are displayed in place of column names. Alias names are given to the right of a column name, enclosed with in double quotes. List the name, salary and PF (10% of salary) of all the employees. SQL> SELECT, SAL, SAL*10/100 "PF" FROM EMP; SAL PF SMITH ALLEN WARD JONES MARTIN BLAKE CLARK

9 SCOTT KING TURNER ADAMS JAMES FORD MILLER ORDER BY: ASHOK GARG The ORDER BY clause sorts the query output according to the values in one or more selected columns. Multiple columns are ordered one within another, and the user can specify whether to order them in ascending or descending order. Ascending is by default. In place of column names we can use numbers to indicate the fields being used to order the output. These numbers will refer their order in the output. SELECT [DISTINCT]<column-list> <expr> FROM <table>[,<table>][where condition] [ORDER BY <columns>][asc DESC] List the employee name and hiredate in descending order of hiredate. SQL> SELECT, HIREDATE FROM EMP ORDER BY HIREDATE DESC; HIREDATE ADAMS 23-MAY-87 SCOTT 19-APR-87 MILLER 23-JAN-82 JAMES 03-DEC-81 FORD 03-DEC-81 KING 17-NOV-81 MARTIN 28-SEP-81 TURNER 08-SEP-81 CLARK 09-JUN-81 BLAKE 01-MAY-81 JONES 02-APR-81 WARD 22-FEB-81 ALLEN 20-FEB-81 SMITH 17-DEC-80 List the empno, ename and sal in ascending order of salary. SQL> SELECT EMPNO,, SAL FROM EMP ORDER BY SAL; EMPNO SAL JAMES SMITH WARD

10 7654 MARTIN TURNER ADAMS ALLEN MILLER BLAKE CLARK JONES SCOTT FORD KING 7200 ASHOK GARG List the employee no, salary, job and department no in the ascending order of department no and descending order of salary. SQL> SELECT EMPNO, DEPTNO, JOB, SAL FROM EMP ORDER BY DEPTNO, SAL DESC; EMPNO DEPTNO JOB SAL PRESIDENT MANAGER CLERK ANALYST ANALYST MANAGER CLERK CLERK MANAGER SALESMAN SALESMAN SALESMAN SALESMAN CLERK 950 List the employee number, name and salary in the descending order of salary. SQL> SELECT EMPNO,, SAL FROM EMP ORDER BY 3 DESC; EMPNO SAL KING SCOTT FORD JONES CLARK BLAKE MILLER ALLEN ADAMS TURNER

11 7521 WARD MARTIN SMITH JAMES 950 ASHOK GARG List the employee number, name and PF(10% salary) in the descending order of PF. SQL> SELECT EMPNO,, SAL*10/100 "PF" FROM EMP ORDER BY 3 DESC; EMPNO PF KING SCOTT FORD JONES CLARK BLAKE MILLER ALLEN ADAMS TURNER WARD MARTIN SMITH JAMES 95 AGGREGATE FUNCTIONS: The aggregate functions produces a single value for an entire group or table. They are used to produce summarized results. They operate on sets of rows. They return results based on group of rows. By default all rows in a table are treated as one group. The GROUP BY clause of the SELECT statement is used to divide rows into smaller groups. COUNT determines the number of rows or non NULL column values. If * is passed, then the total number of rows is returned. When column name is specified, the NULL values will be ignored. Syntax: COUNT(* [Distinct] ALL Column name) 1. How many persons are working in the company. (EMP table) SQL> SELECT COUNT(*) "NO OF EMPLOYEE" FROM EMP; NO OF EMPLOYEE List the no of jobs available in the company. 11

12 SQL> SELECT COUNT(DISTINCT JOB) "NO OF JOBS" FROM EMP; NO OF JOBS 5 3. List the no of clerks in the company. SQL> SELECT COUNT(*) FROM EMP WHERE JOB='CLERK'; COUNT(*) SUM determines the sum of all selected columns. Syntx: SUM([Distinct ALL ] Column name) Show the total salary payable in department no 20. SQL> SELECT SUM(SAL) "TOTAL SALARY" FROM EMP WHERE DEPTNO=20; TOTAL SALARY MAX determines the largest of all selected values of a column Syntx: MAX(Column name) List the maximum salary payable among Salesmans. SQL> SELECT MAX(SAL) "MAXIMUM SALARY" FROM EMP WHERE DEPTNO=20; MAXIMUM SALARY MIN determines the smallest of all selected values of a column. Syntax: 12

13 MIN(Column name) List the minimum salary payable among dept 30. SQL> SELECT MIN(SAL) FROM EMP WHERE DEPTNO=30; MIN(SAL) AVG determines the average of all select values of a column. Syntax: AVG([Distinct ALL ] Column name) list the average salary in the company. SQL> SELECT AVG(SAL) FROM EMP; AVG(SAL) GROUP BY: The GROUP BY clause is used to divide the rows in a table into smaller groups. The GROUP BY clause is used with SELECT to combine a group of rows based on the values of a particular column or expression. Aggregate functions are used to return summary information for each group. A group of rows within another group is called Nested group. Up to 10 level of nesting is supported in a GROUP by expression. 1. List the department no and number of employees in the company. SQL> SELECT DEPTNO, COUNT(*) "NO OF EMPLOYEES" FROM EMP GROUP BY DEPTNO; DEPTNO NO OF EMPLOYEES List the Job and total salary payable in each job. SQL> SELECT JOB, SUM(SAL) "TOTAL SALARY" FROM EMP GROUP BY JOB; JOB TOTAL SALARY 13

14 ANALYST 8640 CLERK 5558 MANAGER PRESIDENT 7200 SALESMAN List the average salary for each job excluding managers. SQL> SELECT JOB, AVG(SAL) FROM EMP WHERE JOB!='MANAGER' GROUP BY JOB; JOB AVG(SAL) ANALYST 4320 CLERK PRESIDENT 7200 SALESMAN List the total salary for each job within the department. SQL> SELECT DEPTNO, JOB, SUM(SAL) FROM EMP GROUP BY DEPTNO, JOB; DEPTNO JOB SUM(SAL) CLERK MANAGER PRESIDENT ANALYST CLERK MANAGER CLERK MANAGER SALESMAN 5600 HAVING Clause: HAVING Clause is used to specify which groups are to be displayed, that is, restrict the groups that you return on the basis of aggregate functions. 1. List average salary of all the departments employing more than 5 persons. SQL> SELECT DEPTNO, AVG(SAL) FROM EMP GROUP BY DEPTNO HAVING COUNT(*)>5; DEPTNO AVG(SAL) List job of all the employees where minimum salary is less than

15 SQL> SELECT JOB, MIN(SAL) FROM EMP GROUP BY JOB HAVING MIN(SAL)<1000; JOB MIN(SAL) CLERK 950 List the total salary, maximum salary, minimum salary, average salary, no of persons job wise for department no 20 only and display only those rows having average salary greater than 1000 and order the result in the descending order of total salary. SQL> SELECT JOB, SUM(SAL) "TOTAL SALARY", MAX(SAL) "MAXIMUM SALARY", MIN(SAL) "MINIMUM SALARY", COUNT(*) "NO OF EMPLOYEES", AVG(SAL) "AVERAGE SALARY" FROM EMP WHERE DEPTNO=20 GROUP BY JOB HAVING AVG(SAL)>1000 ORDER BY SUM(SAL); JOB TOTAL SALARY MAXIMUM SALARY MINIMUM SALARY NO OF EMPLOYEES AVERAGE SALARY CLERK MANAGER ANALYST