MANAGING DATA(BASES) USING SQL (NON-PROCEDURAL SQL, X401.9)

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1 Technology & Information Management Instructor: Michael Kremer, Ph.D. Class 3 Professional Program: Data Administration and Management MANAGING DATA(BASES) USING SQL (NON-PROCEDURAL SQL, X401.9)

2 AGENDA 5. SQL Data Types and Functions 5.1 Numeric Data 5.2 Temporal Data 5.3 Character Data

3 SQL Data Types and Functions 5.

4 5.1 NUMERIC DATA 69 SQL is not a computational or a procedural language Arithmetic capability is weaker than in many other programming languages SQL standard possesses a wide range of numeric types Database vendors add their own numeric extensions(currency) Exact and Approximate Numeric Data Types Numbers are either classified as exact or approximate: Exact number: Precision (p) and a scale (s) (or accuracy): Precision p (positive integer (1 or greater)) = number of significant digits Scale s (nonnegative integer (0 or greater)) = number of decimal places

5 5.1 NUMERIC DATA 70 Approximate Number: Consists of a mantissa and an exponent Exponent is a signed integer specifying the magnate of the mantissa Approximate numeric value has a precision Precision is a positive integer specifying the number of significant digits in the mantissa

5.1 NUMERIC DATA 71 Rounding is almost always necessary, happens automatically: When different numeric data types are assigned to each other When a numeric value is stored into a column of a table

6 5.1 NUMERIC DATA 71 Rounding is almost always necessary, happens automatically: When different numeric data types are assigned to each other When a numeric value is stored into a column of a table Explicit rounding using round function: Rounds number n to specified decimal d Number 5 is rounded up d > 0 rounded to d decimals, d=0 Integer, d < 0 rounded to d digits to the left of decimal point

7 5.1 NUMERIC DATA 72 Truncation function: trunc simply drops digits without rounding Decimal d can be positive, negative, or zero Digit 5 is not rounded up

8 5.1 NUMERIC DATA 73 Data type conversion is common and sometimes necessary Oracle does not allow types to be mixed in one column, even in memory 3 main conversion functions: Use to_number function to convert a string into a number for storing it into the database as a number type Use to_char function to format a number for displaying purposes (such as currency symbol, leading/trailing zeros, thousand separators, etc.)

9 5.1 NUMERIC DATA 74 Formatting symbols for TO_CHAR function for number types:

10 5.1 NUMERIC DATA 75 Oracle specific numeric functions:

11 5.1 NUMERIC DATA 76 Many of these functions are vendor specific Most database platforms have similar functions

greater numbers move towards zero COALESCE function returns the

12 5.1 NUMERIC DATA 77 CEIL function returns the smallest integer greater than or equal to the decimal value For negative numbers, greater numbers move towards zero COALESCE function returns the first non-null value in the list of columns provided as arguments for the function

13 5.1 NUMERIC DATA 78 COUNT(*) counts all records in a table COUNT(col) counts only non-null values of col COUNT(*) of employees table returns 107 records COUNT(manager_id) returns only 106 records

14 5.1 NUMERIC DATA 79 EXP function FLOOR function, opposite behavior of CEIL function GREATEST function: Returns highest value of columns per row

15 5.1 NUMERIC DATA 80 LEAST function: opposite of GREATEST Natural logarithm (LN) and logarithm (LOG) functions

16 5.1 NUMERIC DATA 81 MIN, MAX MEDIAN functions

17 5.1 NUMERIC DATA 82 Nesting of functions call a function within another function Sales_by_quarter lists sales by quarter (horizontally) and by year (vertically) What is the highest value in this matrix GREATEST function nested inside MAX function

18 5.1 NUMERIC DATA 83 REMAINDER and MOD function are very similar MOD function uses FLOOR of quotient to determine the nearest integer REMAINDER uses ROUND

19 5.1 NUMERIC DATA 84 NVL Function: Replace NULL with something else Numeric context: Replace NULL with zero

20 5.1 NUMERIC DATA 85 NVL2 Function: Replace NULL with a specific value (like NVL) Replace NON-NULL with another value Convert column values into two-valued logic, non-null and null values

21 5.1 NUMERIC DATA 86 POWER function SIGN function (3-valued logic) SQRT function (square root) STDEV, VARIANCE

22 5.2 TEMPORAL DATA 87 Calendar year has days, over time misaligned with seasons leap day (0.25 x 4 years = 1 day) Still, fraction (0.0022) adds up over time, in 1582 two weeks were dropped! Abbreviations A.D and B.C replaced by C.E. (Common Era) and B.C.E (Before Common Era) Beginning of the year varies from country to country Format of dates varies by region Standard SQL date format: yyyy-mm-dd Timestamp can be either local or UTC/GMT Daylight saving times further complicates dealing with dates and times across time zones

23 5.2 TEMPORAL DATA 88 All databases have a DATE/TIME data type Point in time Timestamp data type for more precision (fractional seconds) SQL standard contains Interval data type (Day, Hour, Minute, Second) Duration of time Oracle stores dates internally as 7 byte fields: TIMESTAMP Data Type Extends DATE type to support more precise time values Includes all DATE type components plus fractional seconds (nanoseconds precision) INTERVAL Data Type Common part of our life: age of person, maturity period of bonds Two types of Interval:

24 5.2 TEMPORAL DATA 89 Standard SQL has a full set of operators for all these date data types No database vendor has fully implement it Database vendor implemented their own functions before standard

25 5.2 TEMPORAL DATA 90 Default format in Oracle is: dd-mon-yy or dd-mon-yyyy Default format is used when no format is specified Use TO_CHAR function to format date/time data stored in the database (DB User) Use TO_DATE function to store string of date using a format into the database (User/App DB)

26 5.2 TEMPORAL DATA 91 TO_CHAR Current Date, SYSDATE

27 5.2 TEMPORAL DATA 92 ADD_MONTHS GREATEST, LEAST

28 5.2 TEMPORAL DATA 93 INTERVAL LAST_DAY Particularly useful when determining last day in February (leap day?)

29 5.2 TEMPORAL DATA 94 LAST_DAY function is very useful Other database may not have this function Build your own LAST_DAY function using existing, other functions

30 5.2 TEMPORAL DATA 95 MIN, MAX MONTHS_BETWEEN NEXT_DAY

31 5.2 TEMPORAL DATA 96 ROUND function TRUNC function

32 5.3 CHARACTER DATA 97 Character data was fixed-length in SQL 89 (char(n)) SQL 92 added varying character data type (varchar(n)) Varchar(10) is a varying character with a maximum length 10 SQL 92 allows DBA to define collating sequence, the order of characters Character strings are printable characters enclosed in single quotation marks Cannot use double quotes, reserved for database objects

33 5.3 CHARACTER DATA 98 No two languages agree on how to compare character strings as equal unless they are totally equal Is uppercase equal to lowercase letter? Some languages do not even have this concept Most programming languages (including SQL) ignore case in program text but not necessarily in data Equality of strings of unequal length is processed by first padding the shorter string with blanks on the right side until the strings are of the same length. Then they are matched, position for position, for identical values. If one position fails to match, the equality fails SQL 92 defines standard string functions that most vendors support To add strings together, use concatenation operator ( )

34 5.3 CHARACTER DATA 99 SQL String Functions

35 5.3 CHARACTER DATA 100 ASCII Function

36 5.3 CHARACTER DATA 101 INITCAP, LOWER, UPPER Functions Last part shows optimal way to write WHERE clause Convert both sides to either upper or lower case

37 5.3 CHARACTER DATA 102 CHR Function INSTR Function Returns integer position at which substring is found within a string Additional argument allows to specify start position from where to search

38 5.3 CHARACTER DATA 103 LENGTH Function LPAD, RPAD Functions

39 5.3 CHARACTER DATA 104 TRIM Function Removes leading and trailing spaces REVERSE Function Switches characters from right to left

40 5.3 CHARACTER DATA 105 REPLACE Function: Replace one string with another string ( est replaced with ub ) TRANSLATE Function: Replaces string on a character by character basis Unequal lengths: letters dropped

41 5.3 CHARACTER DATA 106 Count number of slashes: Length of original string minus length of string without slashes using replace function SUBSTR Function

42 5.3 CHARACTER DATA 107 INSTR Function Extract filename from filepath

SQL FUNCTIONS. Prepared By:Dr. Vipul Vekariya.

SQL FUNCTIONS. Prepared By:Dr. Vipul Vekariya. SQL FUNCTIONS Prepared By:Dr. Vipul Vekariya. SQL FUNCTIONS Definition of Function Types of SQL Function Numeric Function String Function Conversion Function Date Function SQL Function Sub program of SQL