Database Articles - Page 658 of 671

Different unit values which can be used with MySQL INTERVAL keyword are as follows −MICROSECONDThis unit will be used for adding or subtracting the number of specified microseconds from the current time or as provided by the user.mysql> Select NOW()+INTERVAL 100 MICROSECOND +--------------------------------+ | NOW()+INTERVAL 100 MICROSECOND | +--------------------------------+ | 2017-10-28 18:47:25.000100     | +--------------------------------+ 1 row in set (0.00 sec)Above query will add 100 microseconds to the current date & time with the help of MySQL INTERVAL keyword.mysql> Select '2017-02-25 05:04:30' + INTERVAL 100 Microsecond; +--------------------------------------------------+ | '2017-02-25 05:04:30' + INTERVAL 100 Microsecond | +--------------------------------------------------+ | ... Read More

Suppose if we have stored a date value as ‘0000-00-00’ in MySQL table then on extracting year value from such kind of date, MySQL will return 0. It would not be in either Year(2) or Year(4) format. To understand it we are using the following data from ‘detail_bday’ table −mysql> Select * from detail_bday; +----+---------+------------+ | Sr | Name    | Birth_Date | +----+---------+------------+ | 1 | Saurabh  | 1990-05-12 | | 2 | Raman    | 1993-06-11 | | 3 | Gaurav   | 1984-01-17 | | 4 | Rahul    | 1993-06-11 | | 5 | Sonia   ... Read More

With the help of following MySQL query, we can get the last day of next month −mysql> SELECT LAST_DAY(now() + INTERVAL 1 MONTH) AS 'LAST DAY OF NEXT MONTH'; +------------------------+ | LAST DAY OF NEXT MONTH | +------------------------+ | 2017-11-30             | +------------------------+ 1 row in set (0.00 sec)

With the help of following MySQL query, we can get the last day of previous month −mysql> SELECT LAST_DAY(now() - INTERVAL 1 MONTH) AS 'LAST DAY OF PREVIOUS MONTH'; +----------------------------+ | LAST DAY OF PREVIOUS MONTH | +----------------------------+ | 2017-09-30                 | +----------------------------+ 1 row in set (0.00 sec)

Yes, we can use DESCRIBE or EXPLAIN statements instead of SHOW COLUMNS statement to get the list of the columns in an existing table. In the example below we have applied DESCRIBE and EXPLAIN statement on ‘Employee’ table and got the same result set as got after SHOW COLUMNS statement −mysql> DESCRIBE Employee\G *************************** 1. row ***************************   Field: Id    Type: int(11)    Null: YES     Key: Default: NULL   Extra: *************************** 2. row ***************************   Field: Name    Type: varchar(20)    Null: YES     Key: Default: NULL   Extra: 2 rows in set (0.05 sec) ... Read More

Suppose if we forgot the names of the columns in an existing table then we can use SHOW COLUMNS statement as follows to get the list of columns −mysql> SHOW COLUMNS from Employee\G *************************** 1. row ***************************   Field: Id    Type: int(11)    Null: YES     Key: Default: NULL   Extra: *************************** 2. row ***************************   Field: Name    Type: varchar(20)    Null: YES     Key: Default: NULL   Extra: 2 rows in set (0.07 sec)In the example above, we got the list of columns of ‘Employee’ table with the help of SHOW COLUMNS statement.

As we know that we can copy the data and structure from an existing table by CTAS script. If we want to copy data with some condition/s then we need to use WHERE clause with CTAS script. Consider the example below −mysql> Create table EMP_BACKUP2 AS SELECT * from EMPLOYEE WHERE id = 300 AND Name = 'Mohan'; Query OK, 1 row affected (0.14 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> Select * from EMP_BACKUP2; +------+-------+ | Id   | Name  | +------+-------+ | 300  | Mohan | +------+-------+ 1 row in set (0.00 sec)In the example ... Read More

As we know that we can copy the data and structure from an existing table by CTAS script. If we want to select some specific column/s from another table then we need to mention them after SELECT. Consider the following example in which we have created a table named EMP_BACKUP1 by selecting a specific column ‘name’ from already existing table ‘Employee’ −mysql> Create table EMP_BACKUP1 AS Select name from employee; Query OK, 3 rows affected (0.25 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> Select * from EMP_BACKUP1; +--------+ | name   | +--------+ | Ram    | | ... Read More

With the help of following MySQL query, we can get the last day of the current month −mysql> SELECT LAST_DAY(now()) AS 'LAST DAY OF CURRENT MONTH'; +---------------------------+ | LAST DAY OF CURRENT MONTH | +---------------------------+ | 2017-10-31                | +---------------------------+ 1 row in set (0.00 sec)

With the help of following MySQL query, we can get the first day of next month −mysql> SELECT DATE_FORMAT(CURDATE() + INTERVAL 1 MONTH,'%Y-%m-01') AS 'FIRST DAY OF NEXT MONTH'; +-------------------------+ | FIRST DAY OF NEXT MONTH | +-------------------------+ | 2017-11-01              | +-------------------------+ 1 row in set (0.00 sec)