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MySQLi Articles
Page 116 of 341
What MySQL returns when we remove all the columns from a table by using ALTER TABLE command with DROP keyword?
Eventually, we cannot remove all the columns from a table by using ALTER TABLE command with DROP keyword. In this case, MySQL will return an error message. It is demonstrated with the help of the following exampleSuppose in table ‘Employee’ we have two columns ‘name’ and ‘id’, now if we will use ALTER TABLE to remove both the columns then MySQL returns an error as followsmysql> ALTER TABLE employee drop column name, drop column id; ERROR 1090 (42000): You can't delete all columns with ALTER TABLE; use DROP TABLE instead
Read MoreWhy MySQL uses the interval like 7 day and 2 hour instead of 7 days and 2 hours?
The reason behind this concept is that MySQL requires the unit keywords to be singular, regardless of the English grammar rules. If we will try to supply intervals like 7 days, 2 hours etc then MySQL will produce syntax error as follows −mysql> Select '2017-02-25 05:04:30' + INTERVAL 2 days; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'days' at line 1
Read MoreHow to get the first day of the previous month in MySQL?
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)
Read MoreHow to get the first day of next month in MySQL?
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)
Read MoreHow can we create a new MySQL table by selecting specific column/s from another existing table?
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 MoreHow can we copy data with some condition/s from existing MySQL table?
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 MoreHow can we get a list of columns in an existing MySQL table?
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.
Read MoreHow to get last day of the next month in MySQL?
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)
Read MoreIn which format Year(2) or Year(4) MySQL will return the value of year from date '0000-00-00'?
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 MoreWhat do you mean by default MySQL database for the user?
Actually, there is no default database for the user. But we have default database for the current session. It can be seen from the following query −mysql> Select Database(); +------------+ | Database() | +------------+ | sample | +------------+ 1 row in set (0.00 sec)The above result set shows that we are using ‘sample’ database currently. It is set for the current session. We can set another database, with the help of USE statement, also for the current session as follows −mysql> USE query; Database changed mysql> Select Database(); +------------+ | Database() | +------------+ | query ...
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