We have to use GROUP BY clause if we want to use group functions with non-group fields in the SELECT query. The general syntax can be as followsSyntaxSELECT group_function1, …, non-group-column1, … from table_name GROUP BY column_name;Examplemysql> Select COUNT(*), id from Student GROUP BY id; +----------+------+ | COUNT(*) | id   | +----------+------+ | 1        | 1    | | 1        | 2    | | 1        | 15   | | 1        | 17   | | 1        | 20   | +----------+------+ 5 ... Read More

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 More

As we know that group function operates on the sets of value that is why if group functions will be used in SELECT clause then they will be used on the rows that meet the query selection criteria and the output of group functions will be returned as the output of the query.ExampleIn the example below, we have used some group functions in a SELECT statement on the fields of ‘Student’ table and the output of the statement is the output of those group functions −mysql> Select COUNT(Name), MIN(Id), AVG(Id), MAX(Id), COUNT(*) from Student; +-------------+---------+---------+---------+----------+ | COUNT(Name) | MIN(Id) | ... Read More

As we know that the range of TIME field in MySQL is ‘-838:59:59’ to ‘838:59:59’. Now, if TIMEDIFF() function’s output surpasses this range then MySQL will return either ‘-838:59:59’ or ‘838:59:59’ depends upon the values of the argument. Example mysql> Select TIMEDIFF('2017-09-01 03:05:45', '2017-10-22 03:05:45')AS 'Out of Range TIME Difference'; +------------------------------+ | Out of Range TIME Difference | +------------------------------+ | -838:59:59 | +------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> Select TIMEDIFF('2017-10-22 04:05:45', '2017-09-01 03:05:45')AS 'Out of Range ... Read More

MySQL would return the output in time value after converting the difference between date-and-time values being provided to TIMEDIFF() function as arguments.Example mysql> Select TIMEDIFF('2017-10-22 04:05:45', '2017-10-21 03:04:44')AS 'Difference in Time'; +--------------------+ | Difference in Time | +--------------------+ | 25:01:01           | +--------------------+ 1 row in set (0.00 sec)Here in this example, we can see that MySQL converts the difference in date-and-time values into time values and return the output in time value as well.

With the help of TIMEDIFF() MySQL function the difference between two-time values can be calculated.Examplemysql> Select TIMEDIFF('04:05:45','03:05:45') AS ‘Difference in Time’; +---------------------------------+ | Difference in Time              | +---------------------------------+ | 01:00:00                        | +---------------------------------+ 1 row in set (0.00 sec)

We can use 2-digit year value either in single date expression or in both date expressions used as argument/s in MySQL DATEDIFF() function.For example, the query below is using 2-digit year value in first date expression and other is having 4-digit year value.mysql> Select DATEDIFF('18-10-22', '2017-10-22'); +-----------------------------------+ | DATEDIFF('18-10-22', '2017-10-22') | +-----------------------------------+ |                               365 | +-----------------------------------+ 1 row in set (0.00 sec)And the query below is using 2-digit year value in both date expressions.mysql> Select DATEDIFF('18-10-22', '17-10-22'); +---------------------------------+ | DATEDIFF('18-10-22', '17-10-22') | +---------------------------------+ |   ... Read More

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   | Harshit | Delhi   | Commerce  | | 17   | Raman   | ... Read More

We need to use COUNT(*) function with SELECT clause to count the total number of rows in a table.Examplemysql> Select COUNT(*) from Student; +----------+ | COUNT(*) | +----------+ | 4        | +----------+ 1 row in set (0.06 sec)The query above counts the total number of rows of ‘Student’ table.We can also use WHERE clause with COUNT(*) function as follows:mysql> Select COUNT(*) from Student where Address = 'Delhi'; +----------+ | COUNT(*) | +----------+ | 2        | +----------+ 1 row in set (0.00 sec)

MySQL DATEDIFF() function also works with date and time values but it ignores the time value. Hence even if we include the time value in DATEDIFF() function MySQL will return the difference, in days, between dates by ignoring the time values.mysql> Select DATEDIFF('2018-10-22 04:05:36', '2017-10-22 03:05:45'); +-------------------------------------------------------+ | DATEDIFF('2018-10-22 04:05:36', '2017-10-22 03:05:45') | +-------------------------------------------------------+ |                                                   365 | +-------------------------------------------------------+ 1 row in set (0.00 sec) mysql> Select DATEDIFF('2017-10-22 04:05:36', '2017-10-22 03:05:45'); +-------------------------------------------------------+ | DATEDIFF('2017-10-22 04:05:36', ... Read More