What is the use of FETCH command? OLA interview question
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Answers ( 10 )
The FETCH command cannot be used alone. It has to be used in conjunction with the OFFSET command.
It is used to return a set of number of rows.
The OFFSET argument is used to identify the starting point to return rows from a result set.
Basically, it exclude the first set of records.
Example
SELECT * FROM Employee
ORDER BY Salary
OFFSET 5 ROWS
FETCH NEXT 10 ROWS ONLY;
The above query will skip the first 5 rows and return the next 10 rows.
ORDER BY clause is mandatory to be used with OFFSET and FETCH.
OFFSET value must be greater than or equal to 0. It cannot be negative.
FETCH command is used with OFFSET after ORDER by clause. It returns a set of rows as mentioned by the user
The OFFSET specifies from where to start getting the records, and FETCH will specify till what number of rows that needs to be returned
FETCH command is used to retrieve the rows SEQUENTIALLY.
It is used with OFFSET Command.
SELECT *
FROM Student
ORDER BY Marks
OFFSET 10 ROWS
FETCH NEXT 15 ROWS ONLY
The FETCH argument is used to return a set of number of rows. FETCH can’t be used itself, it is used in conjuction with OFFSET.
Syntax:
SELECT column_name(s)
FROM table_name
ORDER BY column_name
OFFSET rows_to_skip
FETCH NEXT number_of_rows ROWS ONLY;
Example:
Print the Fname, Lname from 3rd to 6th tuple of Employee table when sorted according to the Salary.
SELECT Fname, Lname
FROM Employee
ORDER BY Salary
OFFSET 2 ROWS
FETCH NEXT 4 ROWS ONLY;
The OFFSET FETCH clause allows you to skip N first rows in a result set before starting to return any rows. The FETCH command cannot be used alone. It has to be used in conjunction with the OFFSET command.
To limit the number of rows returned by a query, you use the LIMIT clause. It is widely supported by many database systems However, the LIMIT clause is not a SQL standard clause. SQL:2008 introduced the OFFSET FETCH clause which has a similar function to the LIMIT clause.
Example:
SELECT name, salary FROM employees
ORDER BY salary DESC
OFFSET 5 ROWS
FETCH NEXT 5 ROWS ONLY;
This sorts the employees by salary, skips the first five employees with the highest salary, and fetches the next five ones.
ORDER BY clause is mandatory to be used with OFFSET and FETCH.
OFFSET value must be greater than or equal to 0. It cannot be negative.
The OFFSET FETCH clause is typically used in the client or web applications that require pagination. For example, if each page has ten rows, to get the rows of the second page, you can skip the first ten rows and returns the next ten rows.
FETCH command used with an ORDER BY clause in conjunction with an OFFSET set to retrieve or fetch selected rows sequentially using a cursor that advances through rows and sequentially processes rows one by one till the cursor reaches the terminating condition mentioned in the command.
The essential steps which are involved in declaring a FETCH command are:
1) Declaration of the cursor which will sequentially process each row one at a time
2) Opening of the declared cursor
3) Fetching one row at a time
4) Closing the cursor on the termination condition, i.e. on reaching the last row in the count of rows to be processed (as mentioned as a part of the FETCH command).
syntax:-
SELECT column_name(s)
FROM table_name
ORDER BY column_name
OFFSET starting_point
FETCH NEXT terminating_point ROWS ONLY;
OFFSET and FETCH Clause are used in conjunction with SELECT and ORDER BY clause to provide a means to retrieve a range of records.
SELECT column_name(s)
FROM table_name
ORDER BY column_name
OFFSET rows_to_skip
FETCH NEXT number_of_rows ROWS ONLY;
The FETCH clause specifies the number of rows to return after the OFFSET clause has been processed.
The OFFSET clause specifies the number of rows to skip before starting to return rows from the query.
OFFSET and FETCH clauses must be used with the ORDER BY clause. Otherwise, it returns an error.
ORDER BY column_list [ASC |DESC]
OFFSET offset_row_count {ROW | ROWS}
FETCH {FIRST | NEXT} fetch_row_count {ROW | ROWS} ONLY
*Random example:
SELECT product_name, list_price FROM products
ORDER BY list_price DESC
OFFSET 0 ROWS
FETCH FIRST 10 ROWS ONLY;
This example shows the OFFSET clause is mandatory for the FETCH clause to exist. The FETCH clause is optional. Also, the FIRST and NEXT are synonyms respectively so you can use them interchangeably. Similarly, you can use the FIRST and NEXT interchangeably.
FETCH command is used along with OFFSET.
OFFSET skips first N rows from the beginning and FETCH retrieves the next M rows after the OFFSET has been processed.
ORDER BY clause is mandatory to be used with OFFSET and FETCH.
e.g.
SELECT * FROM Employee
ORDER BY Name
OFFSET 10 ROWS
FETCH NEXT 5 ROWS ONLY;
After ordering by Name column, This query will skip the first 10 rows and return the next 5 rows.
FETCH command is used to return a set number of rows. It cannot be used alone and is always used in conjunction with the OFFSET command. ORDER BY co9mmand is also mandatory to be used.
Syntax:
SELECT (col1, col2, …)
FROM table_name
ORDER BY col_name
OFFSET num_of _rows_to_offset ROWS
FETCH NEXT num_of_rows_reqd ROWS ONLY;