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In MySQL, we can insert current date and time automatically to a column on inserting the NULL values in other columns by declaring that column as DEFAULT CURRENT_TIMESTAMP. In this case, we cannot declare the column NOT NULL in which we want to insert NULL values.mysql> Create Table Testing1(Name Varchar(20), RegStudent TIMESTAMP DEFAULT CURRENT_TIMESTAMP); Query OK, 0 rows affected (0.15 sec)Above query will create a table ‘Testing1’ with a column named ‘Name’(not declared ‘NOT NULL’) and other column named ‘RegDate’ declared as DEFAULT CURRENT_TIMESTAMP. Now, on inserting the NULL values Name column, the current date and time will be inserted ... Read More
With the help of following MySQL query, we can get the first day of previous month −mysql> SELECT DATE_FORMAT(CURDATE() - INTERVAL 1 MONTH,'%Y-%m-01') AS 'FIRST DAY OF PREVOIUS MONTH'; +-----------------------------+ | FIRST DAY OF PREVOIUS MONTH | +-----------------------------+ | 2017-09-01 | +-----------------------------+ 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)
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)
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
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
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.
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
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)
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)