SQL Server/T-SQL/Subquery/Subqueries Exists

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EXISTS evaluates to true if its result contains at least one row

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3> 4> CREATE TABLE works_on (emp_no INTEGER NOT NULL, 5> project_no CHAR(4) NOT NULL, 6> job CHAR (15) NULL, 7> enter_date DATETIME NULL) 8> 9> insert into works_on values (1, "p1", "analyst", "1997.10.1") 10> insert into works_on values (1, "p3", "manager", "1999.1.1") 11> insert into works_on values (2, "p2", "clerk", "1998.2.15") 12> insert into works_on values (2, "p2", NULL, "1998.6.1") 13> insert into works_on values (3, "p2", NULL, "1997.12.15") 14> insert into works_on values (4, "p3", "analyst", "1998.10.15") 15> insert into works_on values (5, "p1", "manager", "1998.4.15") 16> insert into works_on values (6, "p1", NULL, "1998.8.1") 17> insert into works_on values (7, "p2", "clerk", "1999.2.1") 18> insert into works_on values (8, "p3", "clerk", "1997.11.15") 19> insert into works_on values (7, "p1", "clerk", "1998.1.4") 20> GO (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) 1> 2> -- EXISTS evaluates to true if its result contains at least one row 3> 4> SELECT job FROM works_on WHERE exists (SELECT emp_no FROM employee) 5> GO job


analyst manager clerk NULL NULL analyst manager NULL clerk clerk clerk (11 rows affected) 1> 2> drop table works_on 3> GO 1>

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EXISTS Function and Subqueries

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17> 18> CREATE TABLE employee (emp_no INTEGER NOT NULL, 19> emp_fname CHAR(20) NOT NULL, 20> emp_lname CHAR(20) NOT NULL, 21> dept_no CHAR(4) NULL) 22> 23> insert into employee values(1, "Matthew", "Smith", "d3") 24> insert into employee values(2, "Ann", "Jones", "d3") 25> insert into employee values(3, "John", "Barrimore","d1") 26> insert into employee values(4, "James", "James", "d2") 27> insert into employee values(5, "Elsa", "Bertoni", "d2") 28> insert into employee values(6, "Elke", "Hansel", "d2") 29> insert into employee values(7, "Sybill", "Moser", "d1") 30> 31> select * from employee 32> GO (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) emp_no emp_fname emp_lname dept_no


-------------------- -------------------- -------
         1 Matthew              Smith                d3
         2 Ann                  Jones                d3
         3 John                 Barrimore            d1
         4 James                James                d2
         5 Elsa                 Bertoni              d2
         6 Elke                 Hansel               d2
         7 Sybill               Moser                d1

(7 rows affected) 1> 2> CREATE TABLE works_on (emp_no INTEGER NOT NULL, 3> project_no CHAR(4) NOT NULL, 4> job CHAR (15) NULL, 5> enter_date DATETIME NULL) 6> 7> insert into works_on values (1, "p1", "analyst", "1997.10.1") 8> insert into works_on values (1, "p3", "manager", "1999.1.1") 9> insert into works_on values (2, "p2", "clerk", "1998.2.15") 10> insert into works_on values (2, "p2", NULL, "1998.6.1") 11> insert into works_on values (3, "p2", NULL, "1997.12.15") 12> insert into works_on values (4, "p3", "analyst", "1998.10.15") 13> insert into works_on values (5, "p1", "manager", "1998.4.15") 14> insert into works_on values (6, "p1", NULL, "1998.8.1") 15> insert into works_on values (7, "p2", "clerk", "1999.2.1") 16> insert into works_on values (8, "p3", "clerk", "1997.11.15") 17> insert into works_on values (7, "p1", "clerk", "1998.1.4") 18> 19> select * from works_on 20> GO (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) (1 rows affected) emp_no project_no job enter_date


---------- --------------- -----------------------
         1 p1         analyst         1997-10-01 00:00:00.000
         1 p3         manager         1999-01-01 00:00:00.000
         2 p2         clerk           1998-02-15 00:00:00.000
         2 p2         NULL            1998-06-01 00:00:00.000
         3 p2         NULL            1997-12-15 00:00:00.000
         4 p3         analyst         1998-10-15 00:00:00.000
         5 p1         manager         1998-04-15 00:00:00.000
         6 p1         NULL            1998-08-01 00:00:00.000
         7 p2         clerk           1999-02-01 00:00:00.000
         8 p3         clerk           1997-11-15 00:00:00.000
         7 p1         clerk           1998-01-04 00:00:00.000

(11 rows affected) 1> -- EXISTS Function and Subqueries 2> 3> -- EXISTS function takes a subquery as an argument and returns true if the subquery returns one or more rows, and it returns false if the subquery returns zero rows. 4> 5> SELECT emp_lname FROM employee WHERE EXISTS 6> (SELECT * FROM works_on WHERE employee.emp_no = works_on.emp_no AND project_no="p1") 7> 8> drop table works_on 9> drop table employee 10> GO emp_lname


Smith Bertoni Hansel Moser (4 rows affected) 1>

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NOT EXISTS(): Add the NOT operator before the EXISTS statement

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1> create table employee( 2> ID int, 3> name nvarchar (10), 4> salary int ) 5> GO 1> 2> create table job( 3> ID int, 4> title nvarchar (10), 5> averageSalary int) 6> GO 1> 2> 3> insert into employee (ID, name, salary) values (1, "Jason", 1234) 4> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (2, "Robert", 4321) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (3, "Celia", 5432) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (4, "Linda", 3456) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (5, "David", 7654) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (6, "James", 4567) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (7, "Alison", 8744) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (8, "Chris", 9875) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (9, "Mary", 2345) 2> GO (1 rows affected) 1> 2> insert into job(ID, title, averageSalary) values(1,"Developer",3000) 3> GO (1 rows affected) 1> insert into job(ID, title, averageSalary) values(2,"Tester", 4000) 2> GO (1 rows affected) 1> insert into job(ID, title, averageSalary) values(3,"Designer", 5000) 2> GO (1 rows affected) 1> insert into job(ID, title, averageSalary) values(4,"Programmer", 6000) 2> GO (1 rows affected) 1> 2> 3> select * from employee; 4> GO ID name salary


---------- -----------
         1 Jason             1234
         2 Robert            4321
         3 Celia             5432
         4 Linda             3456
         5 David             7654
         6 James             4567
         7 Alison            8744
         8 Chris             9875
         9 Mary              2345

(9 rows affected) 1> select * from job; 2> GO ID title averageSalary


---------- -------------
         1 Developer           3000
         2 Tester              4000
         3 Designer            5000
         4 Programmer          6000

(4 rows affected) 1> 2> 3> -- NOT EXISTS() Add the NOT operator before the EXISTS statement: 4> 5> SELECT ID, Name 6> FROM Employee 7> WHERE NOT EXISTS 8> (SELECT * FROM Job 9> WHERE ID = Employee.ID) 10> GO ID Name


----------
         5 David
         6 James
         7 Alison
         8 Chris
         9 Mary

(5 rows affected) 1> 2> 3> 4> drop table employee; 5> drop table job; 6> GO 1>

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Using the EXISTS() Function

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1> 2> create table employee( 3> ID int, 4> name nvarchar (10), 5> salary int ) 6> GO 1> 2> create table job( 3> ID int, 4> title nvarchar (10), 5> averageSalary int) 6> GO 1> 2> 3> insert into employee (ID, name, salary) values (1, "Jason", 1234) 4> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (2, "Robert", 4321) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (3, "Celia", 5432) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (4, "Linda", 3456) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (5, "David", 7654) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (6, "James", 4567) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (7, "Alison", 8744) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (8, "Chris", 9875) 2> GO (1 rows affected) 1> insert into employee (ID, name, salary) values (9, "Mary", 2345) 2> GO (1 rows affected) 1> 2> insert into job(ID, title, averageSalary) values(1,"Developer",3000) 3> GO (1 rows affected) 1> insert into job(ID, title, averageSalary) values(2,"Tester", 4000) 2> GO (1 rows affected) 1> insert into job(ID, title, averageSalary) values(3,"Designer", 5000) 2> GO (1 rows affected) 1> insert into job(ID, title, averageSalary) values(4,"Programmer", 6000) 2> GO (1 rows affected) 1> 2> 3> select * from employee; 4> GO ID name salary


---------- -----------
         1 Jason             1234
         2 Robert            4321
         3 Celia             5432
         4 Linda             3456
         5 David             7654
         6 James             4567
         7 Alison            8744
         8 Chris             9875
         9 Mary              2345

(9 rows affected) 1> select * from job; 2> GO ID title averageSalary


---------- -------------
         1 Developer           3000
         2 Tester              4000
         3 Designer            5000
         4 Programmer          6000

(4 rows affected) 1> 2> 3> -- Using the EXISTS() Function 4> 5> -- It doesn"t really matter what column or columns are returned in the subquery because you don"t actually use these values. 6> 7> SELECT ID, Name 8> FROM Employee 9> WHERE EXISTS 10> (SELECT * FROM Job 11> WHERE ID = Employee.ID) 12> GO ID Name


----------
         1 Jason
         2 Robert
         3 Celia
         4 Linda

(4 rows affected) 1> 2> drop table employee; 3> drop table job; 4> GO 1>

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