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Articles on Trending Technologies
Technical articles with clear explanations and examples
How can we apply filtering criteria at group levels of the result set returned by MySQL?
As we know that GROUP BY clause in a SELECT statement can divide the result set, returned by MySQL, in groups. Now if we want to return only some specific groups then need to apply filtering criteria at the group level. It can be done by using HAVING clause inside the GROUP BY clause. The example below will demonstrate it −ExampleSuppose we want to return only the group which is having an average salary of 55000 then we need to use filtering criteria as follows in HAVING clause −mysql> Select count(*), AVG(salary), Designation from employees GROUP BY designation having AVG(salary) ...
Read MoreHow can we divide the result set returned by MySQL into groups?
It can be done by using GROUP BY clause in the SELECT statement. We can specify a column as grouping criteria with the help of GROUP BY clause. Due to the specified grouping criteria, rows with the same value in a particular column are considered as a single group. In this way, the result set returned by MySQL SELECT statement will be divided into groups.ExampleFollowing is a good example to understand it −We have a table named ‘employees’ as follows −mysql> Select * from employees; +------+-------------+--------+------------+ | id | designation | Salary | DoJ | +------+-------------+--------+------------+ ...
Read MoreOn passing an out-of-range value in UNIX_TIMESTAMP() or FROM_UNIXTIME() function, what MySQL will return?
When we pass an out-of-range value in UNIX_TIMESTAMP, MySQL returns 0. The valid range of value is same as for the TIMESTAMP data type.Examplemysql> Select UNIX_TIMESTAMP('1969-01-01 04:05:45'); +---------------------------------------+ | UNIX_TIMESTAMP('1969-01-01 04:05:45') | +---------------------------------------+ | 0 | +---------------------------------------+ 1 row in set (0.00 sec)When we pass an out-of-range value in FROM_UNIXTIME, MySQL returns NULL. The valid range of values is same as for the INTEGER data type.Examplemysql> Select FROM_UNIXTIME(2147483648); +---------------------------+ | FROM_UNIXTIME(2147483648) | +---------------------------+ | NULL | +---------------------------+ 1 row in set (0.00 sec)
Read MoreWhat MySQL will return on adding microseconds in the timestamp value for converting it into an integer?
As we know that the value of timestamp can be converted to a number of seconds with the help of UNIX_TIMESTAMP() function. MySQL would ignore the microseconds added to the value of timestamp because the value of UNIX_TIMESTAMP is only 10digits long.Examplemysql> SELECT UNIX_TIMESTAMP('2017-10-22 04:05:36')AS 'Total Number of Seconds'; +-------------------------+ | Total Number of Seconds | +-------------------------+ | 1508625336 | +-------------------------+ 1 row in set (0.00 sec) mysql> SELECT UNIX_TIMESTAMP('2017-10-22 04:05:36.200000')AS 'Total Number of Seconds'; +-------------------------+ | Total Number of Seconds | +-------------------------+ | 1508625336 | +-------------------------+ ...
Read MoreHow is it possible to filter out the duplications in the rows of result set return by MySQL?
It can be possible by using the DISTINCT keyword in SELECT clause. The DISTINCT applies to the combination of all data fields specified in SELECT clause.ExampleWe have the table ‘Student’ on which we have applied DISTINCT keyword as follows −mysql> Select * from student; +------+---------+---------+-----------+ | Id | Name | Address | Subject | +------+---------+---------+-----------+ | 1 | Gaurav | Delhi | Computers | | 2 | Aarav | Mumbai | History | | 15 | ...
Read MoreWhat is the difference between UNIX TIMESTAMPS and MySQL TIMESTAMPS?
In MySQL, UNIX TIMESTAMPS are stored as 32-bit integers. On the other hand MySQL TIMESTAMPS are also stored in similar manner but represented in readable YYYY-MM-DD HH:MM:SS format.Examplemysql> Select UNIX_TIMESTAMP('2017-09-25 02:05:45') AS 'UNIXTIMESTAMP VALUE'; +---------------------+ | UNIXTIMESTAMP VALUE | +---------------------+ | 1506285345 | +---------------------+ 1 row in set (0.00 sec)The query above shows that UNIX TIMESTAMPS values are stored as 32 bit integers whose range is same as MySQL INTEGER data type range.mysql> Select FROM_UNIXTIME(1506283345) AS 'MySQLTIMESTAMP VALUE'; +----------------------+ | MySQLTIMESTAMP VALUE | +----------------------+ | 2017-09-25 01:32:25 | +----------------------+ 1 row in set (0.00 sec)The query ...
Read MoreHow to use compound INTERVAL unit in MySQL?
Compound INTERVAL unit keywords are made up of two keywords and separated by an underscore (_). For using them in MySQL the unit values must be enclosed in single quotes and separated by space.Example − Following query will add 2 years and 2 months in the date value.mysql> Select timestamp('2017-10-22 04:05:36' + INTERVAL '2 2' year_month) AS'Date After 2 Years and 2 Months'; +---------------------------------+ | Date After 2 Years and 2 Months | +---------------------------------+ | 2019-12-22 04:05:36 | +---------------------------------+ 1 row in set (0.00 sec)
Read MoreHow can we sort MySQL output in ascending order?
We need to specify ASC (short form for ASCENDING) keyword in ORDER BY clause if we want to sort out the result set in ascending order.SyntaxSelect column1, column2,…,columN From table_name ORDER BY column1[column2,…] ASC;ExampleIn the following example, we have sorted the result set by column ‘Name’ in the ascending order.mysql> Select * from Student ORDER BY Name ASC; +------+---------+---------+-----------+ | Id | Name | Address | Subject | +------+---------+---------+-----------+ | 2 | Aarav | Mumbai | History | | 1 | Gaurav | Delhi | Computers | | 15 | Harshit | Delhi | Commerce | | 17 | Raman | Shimla | Computers | +------+---------+---------+-----------+ 4 rows in set (0.00 sec)
Read MoreHow can we get sorted output based on multiple columns?
We can specify multiple columns in ORDER BY clause to get the sorted output based on those multiple columns. Following as an example to make this concept clearer −mysql> Select * from Student ORDER BY Name, Address; +------+---------+---------+-----------+ | Id | Name | Address | Subject | +------+---------+---------+-----------+ | 2 | Aarav | Mumbai | History | | 1 | Gaurav | Delhi | Computers | | 15 | Harshit | Delhi | Commerce | | 17 | Raman | Shimla | Computers | +------+---------+---------+-----------+ 4 rows in set (0.12 sec)
Read MoreHow can I use the arithmetic operators (+,-,*,/) with unit values of INTERVAL keyword in MySQL?
We can use arithmetic operators (+, -, *, /) with the unit values of INTERVAL keyword as follows −Use of Addition (+)mysql> Select date('2017-10-22' + INTERVAL 2+2 Year) AS 'Date After (2+2)Years'; +------------------------+ | Date After (2+2) Years | +------------------------+ | 2021-10-22 | +------------------------+ 1 row in set (0.00 sec)Use of Subtraction (-)mysql> Select date('2017-10-22' + INTERVAL 2-2 Year) AS 'Date After (2-2)Years'; +------------------------+ | Date After (2-2) Years | +------------------------+ | 2017-10-22 | +------------------------+ 1 row in set (0.00 sec)Use of Multiplication (*)mysql> Select date('2017-10-22' + INTERVAL ...
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