SQL : Query Language Part II CS3431

Sorting: ORDER BY clause SELECT * FROM Student WHERE sNumber >= 1 ORDER BY sNumber, sName  (sNumber, sName) ( (sNumber >= 1) (Student)) CS3431

Subqueries Subquery returns a relation Nest subqueries into WHERE clause Nest subqueries into FROM clause CS3431

Subqueries SELECT * FROM Student WHERE professor = (SELECT pName FROM Professor WHERE pNumber=1) Note: The inner subquery returns a relation, but SQL runtime ensures that subquery returns a relation with one column and with one row, otherwise it is a run-time error. CS3431

Subqueries - Example Student SELECT * FROM Student WHERE professor = (SELECT pName FROM Professor WHERE pNumber=1) sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER Professor pNumber pName address 1 MM 141FL 2 ER 201FL sNumber sName address professor 1 Dave 320FL MM 2 Greg CS3431

Subqueries We can use IN, EXISTS, NOT IN, and NOT EXISTS ALL, ANY can be used with comparisons SELECT * FROM Student WHERE (sNumber, professor) IN (SELECT pNumber, pName FROM Professor) CS3431

Subqueries - Example Student Professor SELECT * FROM Student sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER pNumber pName address 1 MM 141FL 2 ER 201FL SELECT * FROM Student WHERE (sNumber, professor) IN (SELECT pNumber, pName FROM Professor) sNumber sName address professor 1 Dave 320FL MM CS3431

Subqueries: EXISTS Professor Student SELECT * FROM Student WHERE EXISTS (SELECT pName FROM Professor WHERE Student.professor=pName) Professor pNumber pName address 1 MM 141FL 2 ER 201FL Student sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER CS3431

Subqueries with negation SELECT * FROM Student WHERE (sNumber, professor) NOT IN (SELECT pNumber, pName FROM Professor) Professor pNumber pName address 1 MM 141FL 2 ER 201FL Student sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER sNumber sName address professor 2 Greg 320FL MM 3 Matt ER CS3431

Subqueries with negation Student Professor sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER pNumber pName address 1 MM 141FL 2 ER 201FL SELECT * FROM Student WHERE NOT EXISTS (SELECT pName FROM Professor WHERE Student.professor=pName) sNumber sName address professor CS3431

Subqueries: ALL, ANY CS3431

Subqueries: ALL - Example Student Professor sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER pNumber pName address 1 MM 141FL 2 ER 201FL SELECT * FROM Student WHERE sNumber > ALL (SELECT pNumber FROM Professor) sNumber sName address professor 3 Matt 320FL ER CS3431

Subqueries: ANY - Example Student Professor sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER pNumber pName address 1 MM 141FL 2 ER 201FL SELECT * FROM Student WHERE sNumber = ANY (SELECT pNumber FROM Professor) sNumber sName address professor 1 Dave 320FL MM 2 Greg CS3431

Subqueries: NOT ALL - Example Student Professor sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER pNumber pName address 1 MM 141FL 2 ER 201FL SELECT * FROM Student WHERE NOT sNumber > ALL (SELECT pNumber FROM Professor) sNumber sName address professor 1 Dave 320FL MM 2 Greg CS3431

Subqueries: NOT ANY - Example Student Professor sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER pNumber pName address 1 MM 141FL 2 ER 201FL SELECT * FROM Student WHERE NOT sNumber = ANY (SELECT pNumber FROM Professor) sNumber sName address professor 3 Matt 320FL ER CS3431

Subqueries: Correlation CS3431

Subqueries in FROM clause SELECT sName, pName FROM Student, (SELECT * FROM Professor WHERE pNumber=1) WHERE professor=pName; Professor pNumber pName address 1 MM 141FL 2 ER 201FL Student sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER sName pName Dave MM Greg CS3431

Duplicate Elimination SELECT DISTINCT address FROM Student WHERE sNumber >= 1; SELECT DISTINCT * FROM Student; (Student) ( (address) ( (sNumber >= 1) (Student))) Student sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER address 320FL CS3431

Aggregation + GroupBy CS3431

Aggregation Functions SELECT COUNT (*) FROM Student; SELECT COUNT (sNumber) FROM Student; SELECT MIN (sNumber) FROM Student; SELECT MAX (sNumber) FROM Student; SELECT SUM (sNumber) FROM Student; SELECT AVG (sNumber) FROM Student; We can have distinct such as: SELECT COUNT (DISTINCT sNumber) FROM Student CS3431

Grouping SELECT COUNT (sName) as cnum FROM Student GROUP BY address; (COUNT (sName) as snum) ( (address, COUNT (sName)) (Student)) Student sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER COUNT (sName) 3 CS3431

Grouping SELECT address, COUNT (sNumber) FROM Student WHERE sNumber > 1 GROUP BY address HAVING COUNT (sNumber) > 1; Student sNumber sName address professor 1 Dave 320FL MM 2 Greg 3 Matt ER 4 Ben 300FL address COUNT (sNumber) 320FL 2 CS3431

Aggregation and NULLs NULLs are ignored in any aggregation; except COUNT (*) However if the set of attributes to be grouped on has null values, then grouping is done on the null values as well. CS3431

SQL Queries - Summary SELECT [DISTINCT] a1, a2, …, an FROM R1, R2, …, Rm [WHERE C1] [GROUP BY g1, g2, …, gl [HAVING C2]] [ORDER BY o1, o2, …, oj] CS3431