CS Week 10 - Page 1

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1 CS 425 Week 10 Reading: 1. Silberschatz, Krth & Sudarshan, Chapter Objectives: 1. T learn mre abut SQL Functins used in queries. Cncepts: 1. SQL Functins Outline: SQL Functins Single rw functins Character Number Date Cnversin General Multiple rw functins r Grup functins AVG COUNT MAX MIN STDDEV SUM VARIANCE References: 1. See the assigned text bk CS Week 10 - Page 1

2 CS 425: Week 10 Lecture Ntes SQL FUNCTIONS Functins Single rw Functins Multiple rw Functins Single rw functins: These functins perate n single rws nly and return ne result per rw. There are different types f single rw functins. 1. Character 2. Number 3. Date 4. Cnversin 5. General Single rw functins: Manipulate data items Accept arguments and return ne value Act n each rw returned Return ne result per rw May mdify the data type Can be nested Accept arguments which can be a clumn r an expressin. Functin_name[(arg1, arg2, )] Character functins Case-manipulatin functins LOWER LOWER( SQL Curse ) sql curse CS Week 10 - Page 2

3 UPPER UPPER( SQL Curse ) SQL COURSE INITCAP INITCAP( SQL Curse ) Sql Curse Character-manipulatin functins CONCAT CONCAT( Hell, Wrld ) - HellWrld SUBSTR SUBSTR( HellWrld,1,5) - Hell LENGTH LENGTH( HellWrld ) - 10 INSTR INSTR( HellWrld, W ) - 6 LPAD RPAD LPAD(salary, 10, * ) - *****24000 RPAD(salary, 10, * ) 24000***** TRIM TRIM( H FROM HellWrld ) - ellwrld Number Functins ROUND Runds value t specified decimal ROUND(45.926, 2) = TRUNC Truncates value t the specified decimal TRUNC(45.926, 2) = MOD Returns remainder f divisin MOD(1600, 300) = 100 Example : SELECT ROUND(45.923, 2), TRUNC(45.923, 2), MOD(1600, 300) FROM DUAL; Date Functins Oracle database stres dates in an internal numeric frmat: century, year, mnth, day, hurs, minutes, secnds. The default date display frmat is DD-MON-RR. CS Week 10 - Page 3

4 SYSDATE is a functin that returns: Date Time Arithematic with Dates Operatin result descriptin date + number = Date :- adds a number f days t a date date number = Date :- subtracts a number f days t a date date - date = Number f days :- subtracts ne date frm anther date + number/24 = Date:- adds a number f hurs t a date. Date Functins Assume SYSDATE = 25-JUL-95 MONTHS_BETWEEN = number f mnths between tw dates MONTHS_BETWEEN( 01-SEP-95, 11-JAN-94 ) = ADD_MONTHS = add calendar mnths t date ADD_MONTHS( 11- JAN-94, 6) = 11-JUL-94 NEXT_DAY = next day f the date specified NEXT_DAY( 01-SEP-95, FRIDAY) = 08-SEP-95 LAST_DAY = last day f the mnth LAST_DAY( 01-FEB-95 ) = 28-FEB-95 ROUND = rund date ROUND( SYSDATE, MONTH ) = 01-AUG-95 ROUND( SYSDATE, YEAR ) = 01-JAN-96 TRUNC = truncate date TRUNC( SYSDATE, MONTH ) = 01-JUL-95 TRUNC( SYSDATE, YEAR ) = 01-JAN-95 Cnversin functins Implicit data-type cnversin Frm VARCHAR2 r CHAR T NUMBER Frm VARCHAR2 r CHAR T DATE Frm NUMBER T VARCHAR2 Frm DATE T VARCHAR2 CS Week 10 - Page 4

5 Explicit data-type cnversin TO_CHAR TO_CHAR(date, frmat_mdel ) The frmat mdel: Must be enclsed in single qutatin marks and is case sensitive Can include any valid date frmat elemet Has an fm element t remve padded blanks r suppress leading zers. Is separated frm the date value by a cmma. SELECT emp_id, TO_CHAR(hire_date, MM/YY ) Mnth_Hired FROM emplyees WHERE last_name = Higgins ; Answer: /94 TO_NUMBER TO_NUMBER( char[, frmat_mdel ]) TO_DATE TO_DATE( char[, frmat_mdel ]) General Functins NVL (expr1, expr2) Cnverts a null t an actual value Data types that can be used are date, character and number. Data types must match. SELECT last_name, salary, NVL(cmmissin_pct, 0), salary*12) + (salary*12*nvl(cmmissin_pct, 0)) AN_SAL FROM emplyees; NVL2(expr1, expr2, expr3) NVL2 functin examines the first expressin. If the first expressin is nt null, then the NVL2 functin returns the secnd expressin. If the first expressin is null, then the third expressin is returned. SELECT last_name, salary, cmmissin_pct, NVL2(cmmissin_pct, SAL+COMM, SAL ) incme FROM emplyees WHERE dept_id IN(50, 80); CS Week 10 - Page 5

6 NULLIF (expr1, expr2) It cmpares tw expressins. If they are equal, the functin returns null. If they are nt equal, the functin returns the first expressin. Yu cannt specify the unliteral NULL fr the first expressin. SELECT first_name, LENGTH(first_name) expr1, last_name, LENGTH(last_name) expr2 NULLIF(LENGTH(first_name), LENGTH(last_name)) result FROM emplyees; COALESCE(expr1, expr2, expr n) The COALESCE functin returns the first nn null expressin in the list. The advantage f COALESCE functin ver the NVL functin is that the COALESCE functin can take multiple alternate values. If the first expressin is nt null, it returns that expressin; therwise, it des a COALESCE f the remaining expressins. SELECT last_name, COALESCE(cmmissin_pct, salary, 10) cmm FROM emplyes ORDER BY cmmissin_pct; Multiple rw r GROUP functins Unlike single rw functins, grup functins perate n sets f rws t give ne result per grup. These sets may be the whle table r the table split int grups. Syntax SELECT [clumn,] grup_functin(clumn), FROM table [WHERE cnditin] [GROUP BY clumn] [ORDER BY clumn]; Types f GROUP functins AVG SUM We can use AVG and SUM fr numeric data. CS Week 10 - Page 6

7 SELECT AVG(salary), MAX(salary), MIN(salary), SUM(salary) FROM emplyees WHERE jb_id LIKE %REP% ; COUNT COUNT(expr) returns the number f rws with nn-null values fr the expr. COUNT(*) returns the number f rws in a table. COUNT(DISTINCT expr) returns the number f distinct nnnull values f the expr. SELECT COUNT(*) FROM emplyees WHERE dept_id = 50; MAX MIN We can use MIN and MAX fr any data type. SELECT MIN(hire_date), MAX(hire_date) FROM emplyees; STDDEV VARIANCE NOTE: Grup functins ignre null values in the clumn. CS Week 10 - Page 7