Simple Subqueries in select statement : Subquery Basics « Subquery « Oracle PL / SQL






  1. Oracle PL / SQL
  2. Subquery
  3. Subquery Basics

Simple Subqueries in select statement

    
SQL>
SQL>
SQL> CREATE TABLE emp (
  2     empID INT NOT NULL PRIMARY KEY,
  3     Name      VARCHAR(50) NOT NULL);

Table created.

SQL> INSERT INTO emp (empID,Name) VALUES (1,'Tom');

1 row created.

SQL> INSERT INTO emp (empID,Name) VALUES (2,'Jack');

1 row created.

SQL> INSERT INTO emp (empID,Name) VALUES (3,'Mary');

1 row created.

SQL> INSERT INTO emp (empID,Name) VALUES (4,'Bill');

1 row created.

SQL> INSERT INTO emp (empID,Name) VALUES (5,'Cat');

1 row created.

SQL> INSERT INTO emp (empID,Name) VALUES (6,'Victor');

1 row created.

SQL> CREATE TABLE empExam (
  2     empID  INT NOT NULL,
  3     ExamID     INT NOT NULL,
  4     Mark       INT,
  5     IfPassed   SMALLINT,
  6     Comments   VARCHAR(255),
  7     CONSTRAINT PK_empExam PRIMARY KEY (empID, ExamID));

Table created.

SQL>
SQL>
SQL> INSERT INTO empExam (empID,ExamID,Mark,IfPassed,Comments) VALUES (1,1,55,1,'Satisfactory');

1 row created.

SQL> INSERT INTO empExam (empID,ExamID,Mark,IfPassed,Comments) VALUES (1,2,73,1,'Good result');

1 row created.

SQL> INSERT INTO empExam (empID,ExamID,Mark,IfPassed,Comments) VALUES (2,3,44,1,'Hard');

1 row created.

SQL> INSERT INTO empExam (empID,ExamID,Mark,IfPassed,Comments) VALUES (2,5,39,0,'Simple');

1 row created.

SQL> INSERT INTO empExam (empID,ExamID,Mark,IfPassed) VALUES (2,6,63,1);

1 row created.

SQL>
SQL>
SQL>
SQL> SELECT empID, Name,
  2     (SELECT COUNT(*) FROM empExam
  3      WHERE empExam.empID = emp.empID)
  4      AS ExamsTaken
  5  FROM emp
  6  ORDER BY ExamsTaken DESC;

     EMPID NAME                                               EXAMSTAKEN
---------- -------------------------------------------------- ----------
         2 Jack                                                        3
         1 Tom                                                         2
         5 Cat                                                         0
         4 Bill                                                        0
         6 Victor                                                      0
         3 Mary                                                        0

6 rows selected.

SQL>
SQL> drop table empExam;

Table dropped.

SQL> drop table emp;

Table dropped.








Related examples in the same category

1.Use sub query as a virtual table
2.Compare with data from subquery
3.An example of a nested three-level subquery
4.If an inner query returns a NULL, the outer query also returns NULL
5.Working with multi-column subqueries
6.Use aggregate function in sub query
7.Sub query: 'SELECT 1 FROM dept d'
8.Using the EXISTS and NOT EXISTS operators
9.Writing Single Row Subqueries
10.Compare with the sub query result
11.Subqueries in a HAVING Clause: Uses a subquery in the HAVING clause of the outer query
12.Subqueries in a FROM Clause (Inline Views)
13.Single Row Subqueries May Return a Maximum of One Row
14.Subqueries May Not Contain an ORDER BY Clause
15.Sub query with table join
16.Writing Multiple Column Subqueries with table join
17.Subquery just returns a literal value: improve performance of your query
18.EXISTS typically offers better performance than IN with subqueries
19.NVL() is used to convert null in correlated query
20.Writing Nested Subqueries
21.subqueries in the SELECT column list (New Way)
22.subqueries in the SELECT column list (Old way)
23.Not equals and subquery
24.Greater than average salary
25.Greater than max(salary)
26.Larger than value from subquery
27.Subquery in select statement
28.Subquery in where clause
29.Subqueries That Return Multiple Results
30.Subqueries in the WHERE Clause: equals
31.Subqueries in the WHERE Clause: less than
32.Single-row subqueries return only one row of result.
33.The parent query of a single-row subquery can return more than one row.
34.Born after employee 4 was born
35.inline view: What percentage of these items exist in each bin selected