Sql subquery
- 1. SQL Subquery By raveena thakur
- 2. What is SQL Sub query? A sub query is a SQL query nested inside a larger query.
- 3. Where Sub query occurs? A subquery may occurs in: • A SELECT clause • A WHERE clause • The sub query can be nested inside a SELECT, INSERT, UPDATE, or DELETE statement or inside another sub query. • A sub query is usually added within the WHERE clause of another SQL SELECT statement. • You can use the comparison operators, such as >, <, or =. The comparison operator can also be a multiple-row operator, such as IN, ANY, or ALL.
- 4. SUBQUERY SYNTAX • The subquery (inner query) executes before the main query(outer query). • The result of the subquery is used by the main query.
- 5. TYPE OF SUBQUERIES • Single row subquery : Returns zero or one row. • Multiple row subquery : Returns one or more rows. • Multiple column subqueries : Returns one or more columns.
- 6. SINGLE ROW SUBQUERIES • The single row subquery returns one row. The single row query uses any operator in the query i.e. (=,<=, >=, <>, <, > ). • EXAMPLE: • department table Employee table
- 7. • Suppose you want to find out the ename, job,sal of the employees whose salaries are less than that of an employee whose empno= 7876 from EMP table. Now you need to perform two queries in order to get the desired result. 1. We will find out the salary of the employee whose empno=7876. the query is as under: 2. Now in second query we will apply the condition from which we will find the ename, job and sal. We will use the query as under:
- 8. • The above two queries can be used as single query by using the concept of subquery. It will combine the result into a single query as under:
- 9. MULTIPLE ROW SUBQUERY • Returns sets of rows. Query uses the set comparison operators (IN, ALL, ANY). if u use a multirow subquery with the equals comparison operators, the database will return an error if more than one row is returned. SYMBOL MEANING IN Equal to any member in a list. ANY Return rows that match any value on a list. ALL Return rows that match all the values in a list.
- 10. IN Operator • The IN operator retirns true if the comparison value is contained in the list. • The following statement finds the employee whose salary is the same as the minimum salary of the employees in the department.
- 11. ANY Operator • The ANY operator return true if the comparison value matches any of the values in the list. • Display the employees whose salary is more than the minimum salary of the employees in any department.
- 12. ALL Operator • Returns true only if the comparison value matches all the values in the list. • Display the employee detail with salary less than those whose job is ‘MANAGER’.
- 13. MULTIPLE COLUMN SUBQUERY • A subquery that compares more than one column between the parent query and subquery is called the multiple column subqueries. • List the employees that makes the same salary as other employee with empno=7521 with the same job also.
- 14. Deleting Tables • One can delete from a table by using DELETE FROM statement. The DELETE statement removes rows from a table, but it does not release storage space. • SYNTAX: DELETE FROM table_name; • Example: To remove all rows in the student table, you just execute the following query: DELETE FROM student;
- 15. Thank you