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Chapter 8A Relational Set Operators UNION UNION

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Chapter 8A Relational Set Operators UNION UNION Chapter 8a Relational Set Operators Objectives: to learn Outline • Based on relational algebra/ set operations • the relational set • Relational Set operators Operators • Work properly if relations are union-compatible – UNION, • SEQUENCE Objects – Names of relation attributes must be the same and – UNION ALL, • SQL Built-in Functions their data types must be identical – INTERSECT, and – Numeric • SQL-’99 ANSI Standard commands – MINUS – String – UNION • How to create and use – Date Sequence objects as – Misc – INTERSECT an ‘autonumber’ – Pseudo Columns – MINUS (called ‘EXCEPT’ in the 99 standards) • SQL functions to • Some DMS’s may not implement these. manipulate dates, strings, and other data Fall 2010 - CS275 1 Fall 2010 - CS275 2 UNION UNION ALL • Combines tables eliminating duplicate rows. • Combines tables retaining duplicate rows. • Can be used to unite more than two queries SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, CUS_AREACODE, CUS_PHONE CUS_AREACODE, CUS_PHONE FROM CUSTOMER FROM CUSTOMER UNION ALL UNION SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, SELECT CUS_LNAME, CUS_FNAME,CUS_INITIAL, CUS_AREACODE, CUS_PHONE CUS_AREACODE, CUS_PHONE FROM CUSTOMER_2; FROM CUSTOMER_2; Fall 2010 - CS275 3 Fall 2010 - CS275 4 1 INTERSECT INTERSECT • Combines rows from two queries, returning only SELECT CUS_CODE the rows that appear in both sets. FROM CUSTOMER WHERE CUS_AREACODE = ‘615’ INTERSECT SELECT DISTINCT CUS_CODE • Example: FROM CUSTOMER; SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, FROM CUSTOMER INTERSECT SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, CUS_AREACODE, CUS_PHONE FROM CUSTOMER_2; Fall 2010 - CS275 5 Fall 2010 - CS275 6 Syntax Alternatives - Intersect MINUS • Generalized Syntax: • Combines rows from two queries, returning only Select <columns> the rows that appear in the first set but not in the from t1 where t1.fieldA in (select t2.fieldA from t2); second • Example: solving the previous problem: – Example: Select cus_code SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, from customer CUS_AREACODE, FROM CUSTOMER where cus_areacode= ‘615’ and MINUS cus-code in (select distinct cus_code from SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, Invoice) CUS_AREACODE, FROM CUSTOMER_2 Fall 2010 - CS275 8 Fall 2010 - CS275 7 2 MINUS Syntax Alternatives -Minus Example reversing the tables: SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, • Generalized Syntax CUS_AREACODE, CUS_PHONE FROM CUSTOMER_2 Select <columns> from t1 w here t1.key not in (select MINUS SELECT CUS_LNAME, CUS_FNAME, CUS_INITIAL, t2.key from t2); CUS_AREACODE, CUS_PHONE FROM CUSTOMER • Example starting with previous problem, but using another table(non-union compatiable): Select cus_code from customer where cus_areacode= ‘615’ and cus_code not in (select distinct cus_code from Invoice); • IN and NOT IN subqueries can be used in place of INTERSECT & MINUS Fall 2010 - CS275 9 Fall 2010 - CS275 10 Oracle Sequences Oracle Sequence • Sequence Numbers: allows establishing an • Create sequence <seq_name> start with <n> “autonumber” sequence Increment by <n>; • Oracle sequences – Examples: – Independent object in the database Create sequence cust_code start with 100 – Are named and used anywhere a numeric value is increment by 1; expected Create sequence product_num NOCACHE; – Not tied to a table or column – Generates new numeric values that can be • Viewing your sequences assigned to any column in any table Select * from user_sequences; – A named sequence can be created and deleted at any time Fall 2010 - CS275 11 Fall 2010 - CS275 12 3 Oracle Sequence Oracle Sequence Create sequence cus_code_seq start with 20010 • Sequence numbers are used via a keyword nocache; – NEXTVAL Create sequence inv_number_seq start with 4010 • used to generate a new number • Often used as a primary key for a table row nocache; • Example: Insert into table invoice values (inv_sequence.NEXTVAL, 20010, sysdate); – CURRVAL • Used to retrieve the current value of the sequence. • Cannot directly retrieve attributes from a sequence. • Example: Select inv_sequence.CURRVAL from dual; Fall 2010 - CS275 13 Fall 2010 - CS275 14 Oracle Sequences SQL (non-aggregate) Functions inserting a series of rows with auto sequence • Functions manipulate data items and return a numbers. Insert into customer values ( single result . ( i.e. SQL functions are similar to cus_code_seq.nextval, functions in programming languages.) ‘Connery’, ‘Sean’, NULL, ‘615’, ‘898-2007’, 0.00); • Oracle has more than 150 different functions. (See Insert into Invoice values ( link on our resource page to the Oracle inv_number_seq.nextval, 20010, sysdate); documentation ) Insert into Line values (inv_number_seq.currval, 1, • Functions use numerical, date, or string values, ’13-Q2/P2’, 1, 14.99); which may be part of a command or a table Insert into line values( attribute. inv_number_seq.currval, 2, ‘23109-HB’, 1, 9.95); • The Function may appear anywhere in an SQL statement Fall 2010 - CS275 15 Fall 2010 - CS275 16 4 Numeric Functions SQL Functions - Numeric • Grouped in different ABS(n) -Absolute value of n ways CEIL(n) -Smallest integer greater or equal to n – Algebraic, FLOOR(n) -Largest integer equal to or less than n trigonometric, MOD(m,n) -Remainder of m divided by n logarithmic, etc. POWER(m,n) -m raised to the nth power • Do not confuse with ROUND(n,[m]) -n rounded to m decimal places. aggregate functions SIGN(n) -If n<0 returns -1, if n= 0 returns 0, if – Aggregate functions n>0 returns 1 operate over sets SQRT(n) -Square root of n, if n<0 returns NULL – Numeric functions TRUNC(c[m]) -n truncated to m decimal places operate over single row Fall 2010 - CS275 17 Fall 2010 - CS275 18 String Functions SQL Functions - String • The most used ASCII(str) – Returns ASCII value of first character in str functions are the CHR(n) – Character with ASCII value n String functions CONCAT(str1,str2) – Returns the combined data items. • Examples: Upper/Lower INITCAP(str) – Capitalizes the first letter of each word Substr INSTR(str1,str2[,n[m]]) – Returns the position of the mth occurrence Length of str2, begins search at position n. || - or Concat SUBSTR(str, start, length) – Returns substring of str LENGTH(str) – Returns the length of str LOWER(str) – Forces all letters to lower case L/RPAD(str1,n[,str2]) – Left or Right pads str1 to length n with sequence of characters in str2 (if unspecified, pads with blanks) Fall 2010 - CS275 19 Fall 2010 - CS275 20 5 SQL Functions – String SQL Functions – Date & Time L/RTRIM(str,set) – Removes characters starting from the Left or Right in str up to the first character not in • All SQL-standard DBMSs support date and time set. functions REPLACE(str,’literal1’,’literal2’) • Date functions take one parameter – Search str for 1st string and replace w/2nd • Commonly used Functions: string. Similar to translate. ADD_MONTHS(d,n) – Date d plus n months SOUNDEX(str) – Returns a str value representing the sound of the word(s) in str. LAST_DAY(d) – Date of last day of month containing d SUBSTR(str,m[,n]) – Returns substring of str, beginning at MONTHS_BETWEEN(d,e) – Number of months between dates d & e character m, for length of n. TRANSLATE(str,frm,to) – str is translated from the character set frm NEW_TIME(d,a,b) – Date and time in timezone b when d is to the character set to. from timezone a. – Forces all letters to upper case. NEXT_DAY(d,char) – Date of first day of week named by char UPPER(str) => d USERENV(str) – Returns user information for writing audit trails. TRUNC(date) – Date with time of day removed. Fall 2010 - CS275 21 Fall 2010 - CS275 22 SQL Functions - Data Conversions Data Conversion Examples CHARTOROWID(char) – Converts char to a row ID TO_DATE :using character HEXTORAW(char) – Converts char, which must contain a formats to return a date. hexadecimal number to a binary value TO_CHAR: using a date and RAWTOHEX(raw) – Converts raw to char value containing a hex number. returning pieces of the date – Converts a row ID to a char value as character values. ROWIDTOCHAR(rowid) – Converts expr, a number or date value to TO_CHAR(expr[,fmt]) a char value. Format may be used to convert dates. TO_DATE(char[,fmt]) – Converts from char value to a date value. fmt specifies the format of the parameter char TO_DATE(n, fmt) – Converts a number into a date TO_NUMBER(char) – Converts a char value to a number . Fall 2010 - CS275 23 Fall 2010 - CS275 24 6 Data Conversion Examples SQL Functions - Miscellaneous TO_CHAR: converting a number to a • Misc. Functions- data type on item returned is character string variable TO_NUMBER: converting a character DECODE (expr, search1, return1, search2, return2,…[default]) string to a number If expr equals any search, returns the NVL: converts a null to a string following return; DECODE: returns associated value if not, returns default when matched or a default value DUMP (expr[, radix[,start-positions[,bytes]]]) Display the contents of internal data areas GREATEST (expr,expr,..) Returns greatest of a list of values LEAST (expr,expr,…) Returns the least of a list of values NVL (expr1,expr2) If expr1 is null, returns expr2; if expr1 is not null, returns expr1 VSIZE (expr) Returns the number of bytes in ORACLE’s internal representation of expr Fall 2010 - CS275 26 Fall 2010 - CS275 25 SQL Functions -Pseudo-Columns Chapter 8A Summary Level - 1 for root node, 2 for child - used in • Relational set operators combine output of two queries to generate new relation ..Select...Connect By • Set operations using the key words UNION, Null - Returns a null value - used in Insert UNION ALL, INTERSECT, and MINUS are part of statements for blank data the new SQL-’99 extensions. RowID - ID for each row in a table • Oracle sequences may be used to generate values RowNum - Order in which the row was extracted to be assigned to a record Sysdate - Current date and time • SQL functions are used to extract or transform UID - User ID data USER - Name of current user (Login name) • SQL has Numeric, String (Character), Date, Misc./Conversion functions, and Pseudo columns 28 Fall 2010 - CS275 27 Fall 2010 - CS275 7.
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