SQL: Data Manipulation

1. SQL: Data Manipulation Presented by Mary Choi For CS157B Dr. Sin Min Lee

2. Introduction • Structured Query Language (SQL) • Writing an SQL Command • Retrieving Data • Building SQL Statements • Performing Database Updates

3. What is SQL? • SQL is an example of a transform-oriented language. • A language designed to use relations to transform inputs into required outputs. Source: Database Systems Connolly/Begg

4. What is SQL? • ISO SQL has two major components: • Data Definition Language (DDL) • Data Manipulation Language (DML) Source: Database Systems Connolly/Begg

5. Data Definition Language (DDL) • Defining the database structure • Tables • Controlling access to the data • What a user can legally access Source: Database Systems Connolly/Begg

6. Data Manipulation Language (DML) • Retrieving Data • Query tables • Updating Data • Populate tables Source: Database Systems Connolly/Begg

7. Writing SQL Commands • SQL statement consists of reserved words and user-defined words • Reservedwords are a fixed part of the SQL language and have a fixed meaning • User-defined words are made up by the user (according to syntax rules) Source: Database Systems Connolly/Begg

8. Reserved Words • Are fixed part of the SQL language • Have a fixed meaning • Require exact spelling • Kept on the same line Source: Database Systems Connolly/Begg

9. User-defined Words • Are made up by the user • Governed by a set of syntax rules • Represent names of database objects such as: • Tables • Columns • Views • Indexes Source: Database Systems Connolly/Begg

10. Data Manipulation • Select: query data in the database • Insert: insert data into a table • Update: updates data in a table • Delete: delete data from a table Source: Database Systems Connolly/Begg

11. Literals • Non-numeric data values must be enclosed in single quotes: • ’16 Holland Drive’ • ‘CS157B’ • Numeric data values must NOT be enclosed in single quotes: • 6 • 600.00 Source: Database Systems Connolly/Begg

12. Writing SQL Commands Most components of an SQL statement are case insensitive, but one exception is that literal character data must be typed exactly as it appears in the database. Source: Database Systems Connolly/Begg

13. Simple Query • Select specifies which columns are to appear in the output. • From specifies the table(s) to be used. • Where filters the rows subject to some condition(s). Source: Database Systems Connolly/Begg

14. Simple Query • Group By forms groups of rows with the same column value. • Having filters the groups subject to some condition. • Order By specifies the order of the output. Source: Database Systems Connolly/Begg

15. Retrieve all columns and all rows SELECT firstColumn,…,lastColumn FROM tableName; SELECT* FROM tableName;

16. Use of Distinct SELECT DISTINCT columnName FROM tableName;

17. Calculated fields SELECT columnName/2 FROM tableName

18. Comparison Search Condition = equals < > is not equal to (ISO standard) != “ “ “ “ (allowed in some dialects) < is less than > is greater than <= is less than or equal to >= is greater than or equal to Source: Database Systems Connolly/Begg

19. Comparison Search Condition • An expression is evaluated left to right. • Subexpressions in brackets are evaluated first. • NOTs are evaluated before ANDs and ORs. • ANDs are evaluated before ORs. Source: Database Systems Connolly/Begg

20. Range Search Condition SELECT columnName FROM tableName WHERE columnName BETWEEN 20 AND 30; SELECT columnName FROM tableName WHERE columnName >= 20 AND columnName <= 30;

21. Set membership search condition SELECT columnName FROM tableName WHERE columnName IN (‘name1’, ‘name2’); SELECT columnName FROM tableName WHERE columnName = ‘name1’ OR columnName = ‘name2’;

22. Pattern matching symbols % represents any sequence of zero or more characters (wildcard). _ represents any single character Source: Database Systems Connolly/Begg

23. Pattern match search condition ‘h%’ : begins with the character h . ‘h_ _ _’ : four character string beginning with the character h. ‘%e’ : any sequence of characters, of length at least 1, ending with the character e. ‘%CS157B%’ : any sequence of characters of any length containing CS157B Source: Database Systems Connolly/Begg

24. Pattern match search condition LIKE ‘h%’ begins with the character h . NOT LIKE ‘h%’ does not begin with the character h. Source: Database Systems Connolly/Begg

25. Pattern match search condition To search a string that includes a pattern-matching character ‘15%’ Use an escape character to represent the pattern-matching character. LIKE ‘15#%’ ESCAPE ‘#’ Source: Database Systems Connolly/Begg

26. NULL search condition DOES NOT WORK comment = ‘ ’ comment != ‘ ’ DOES WORK comment IS NULL comment IS NOT NULL

27. Sorting • The ORDER BY clause • consists of list of column identifiers that the result is to be sorted on, separated by commas. • Allows the retrieved rows to be ordered by ascending (ASC) or descending (DESC) order Source: Database Systems Connolly/Begg

28. Sorting • Column identifier may be • A column name • A column number (deprecated) Source: Database Systems Connolly/Begg

29. Sorting SELECT type, rent FROM tableName ORDER BY type, rent ASC; Source: Database Systems Connolly/Begg

30. Aggregate Functions • COUNT returns the number … • SUM returns the sum … • AVG returns the average … • MIN returns the smallest … • MAX returns the largest … value in a specified column. Source: Database Systems Connolly/Begg

31. Use of COUNT( * ) How many students in CS157B? SELECT COUNT( * ) AS my count FROM CS157B

32. GROUP BY clause • When GROUP BY is used, each item in the SELECT list must be single-valued per group. • The SELECT clause may contain only • Column names • Aggregate functions • Constants • An expression involving combinations of the above Source: Database Systems Connolly/Begg

33. Grouping SELECTdept,COUNT(staffNo)AS my count SUM(salary) FROM tableName GROUP BY dept ORDER BY dept

34. Restricting Grouping • HAVING clause • is with the GROUPBY clause. • filters groups into resulting table. • includes at least one aggregate function. • WHERE clause • filters individual rows into resulting table. • Aggregate functions cannot be used. Source: Database Systems Connolly/Begg

35. SELECT dept, COUNT(staffNo) AS my count, SUM(salary) AS my sum FROM Staff GROUP BY dept HAVING COUNT(staffNo) > 1 ORDER BY dept; Source: Database Systems Connolly/Begg

36. Subqueries SELECT columnNameA FROM tableName1 WHERE columnNameB = (SELECT columnNameB FROM tableName2 WHERE condition); result from inner SELECT applied as a condition for the outer SELECT Source: Database Systems Connolly/Begg

37. Subquery with Aggregate Function List all staff whose salary is greater than the average salary, show by how much their salary is greater than the average. SELECT fName, salary – ( SELECTAVG(salary) FROM Staff ) AS salDiff FROM Staff WHERE salary > ( SELECT AVG(salary) FROM Staff ); Source: Database Systems Connolly/Begg

38. Nested Subqueries: Use of IN SELECT property FROM PropertyForRent WHERE staff IN( SELECT staff FROM Staff WHERE branch = ( SELECT branch FROM Branch WHERE street = ‘112 A St’)); Selects branch at 112 A St Source: Database Systems Connolly/Begg

39. Nested Subqueries: Use of IN SELECT property FROM PropertyForRent WHERE staff IN( SELECT staff FROM Staff WHERE branch = (branch ) ); Select staff members who works at branch. Source: Database Systems Connolly/Begg

40. Nested Subqueries: Use of IN SELECT property FROM PropertyForRent WHERE staff IN( staffs who works at branch on ‘112 A St’); Since there are more than one row selected, “=“ cannot be used. Source: Database Systems Connolly/Begg

41. Use of ANY/SOME SELECT name, salary FROM Staff WHERE salary > SOME( SELECT salary FROM Staff WHERE branch = ‘A’ ); Result: {list of staff with salary greater than 2000.} Result:{2000,3000,4000} Source: Database Systems Connolly/Begg

42. Use of ALL SELECT name, salary FROM Staff WHERE salary > ALL( SELECT salary FROM Staff WHERE branch = ‘A’ ); Result: {list of staff with salary greater than 4000.} Result:{2000,3000,4000} Source: Database Systems Connolly/Begg

43. Use of Any/Some and All • If the subquery is empty: • ALL returns true • ANY returns false • ISO standard allows SOME to be used interchangeably with ANY. Source: Database Systems Connolly/Begg

44. Multi-Table Queries • Join • Inner Join • Left Outer Join • Right Outer Join • Full Outer Join Source: Database Systems Connolly/Begg

45. Join SELECT client FROM Client c, View v WHERE c.client = v.client; ISO standard Alternatives FROM Client c JOIN View v ON c.client = v.client (creates two identical client columns) FROM Client JOIN View USING client FROM Client NATURALJOIN View Source: Database Systems Connolly/Begg

46. Join • The join operation combines data from two tables by forming pairs of related rows where the matching columns in each table have the same value. • If one row of a table is unmatched, the row is omitted from the resulting table. Source: Database Systems Connolly/Begg

47. Inner Join SELECT b.*,p.* FROM Branch b, Property p WHERE b.bCity = p.pCity; Source: Database Systems Connolly/Begg

48. Inner Join Result SELECT b.*,p.* FROM Branch b, Property p WHERE b.bCity = p.pCity; Source: Database Systems Connolly/Begg

49. Left Outer Join SELECT b.*,p.* FROM Branch b LEFT JOIN Property p ON b.bCity = p.pCity; Source: Database Systems Connolly/Begg

50. Right Outer Join SELECT b.*,p.* FROM Branch b RIGHT JOIN Property p ON b.bCity = p.pCity; Source: Database Systems Connolly/Begg