Article Categories
- All Categories
-
Data Structure
-
Networking
-
RDBMS
-
Operating System
-
Java
-
MS Excel
-
iOS
-
HTML
-
CSS
-
Android
-
Python
-
C Programming
-
C++
-
C#
-
MongoDB
-
MySQL
-
Javascript
-
PHP
-
Economics & Finance
MySQL Articles
Page 102 of 355
How to add columns to an existing MySQL table?
By using ALTER command we can add columns to an existing table.SyntaxAlter table table-name ADD (column-name datatype);Example In the example below, with the help of ALTER Command, column ‘GRADE’ is added to the table ‘Student’.mysql> Alter table Student ADD (Grade Varchar(10)); Query OK, 5 rows affected (1.05 sec) Records: 5 Duplicates: 0 Warnings: 0
Read MoreWhat are the different commands used in MySQL?
SQL language is divided into four types of primary language statements: DML, DDL, DCL and TCL. Using these statements, we can define the structure of a database by creating and altering database objects and we can manipulate data in a table through updates or deletions. We also can control which user can read/write data or manage transactions to create a single unit of work.The four main categories of SQL statements are as follows −DML (Data Manipulation Language)DML statements affect records in a table. These are basic operations we perform on data such as selecting a few records from a table, ...
Read MoreHow can I use INTERVAL keyword with MySQL NOW() and CURDATE() functions?
INTERVAL keyword with NOW() and CURDATE() MySQL functions can be used in similar fashion as it can be used with time, date or datetime units of a date value.ExampleUsing INTERVAL with MySQL NOW()mysql> Select NOW() + INTERVAL 2 day; +------------------------+ | NOW() + INTERVAL 2 day | +------------------------+ | 2017-10-30 09:19:31 | +------------------------+ 1 row in set (0.00 sec) mysql> Select NOW() - INTERVAL 2 day; +------------------------+ | NOW() - INTERVAL 2 day | +------------------------+ | 2017-10-26 09:19:45 | +------------------------+ 1 row in set (0.00 sec) mysql> Select NOW() - INTERVAL 2 hour; +-------------------------+ | NOW() ...
Read MoreHow can we convert TIME and DATETIME values to numeric form in MySQL?
Conversion of TIME(N) and DATETIME(N) values to numeric form can be done by adding 0(+0) to them. Followings are the rules for such kind of conversion −Converted to INTEGERThe TIME(N) and DATETIME(N) values will be converted to an integer when N is 0.For example, the values of CURTIME() and NOW() can be converted to integer values as follows −mysql> SELECT CURTIME(), CURTIME()+0; +-----------+-------------------+ | CURTIME() | CURTIME()+0 | +-----------+-------------------+ | 19:42:54 | 194254 | +-----------+-------------------+ 1 row in set (0.04 sec) mysql> SELECT NOW(), NOW()+0; +-------------------------+----------------------------------+ | NOW() ...
Read MoreWhat is the difference between YEAR(2) and YEAR(4) in MySQL?
YEAR(2) stores a year in 2-digit format. For example, we can write 69 to store 1969 a year. In YEAR (2), the year can be specified from 1970 to 2069 (70 to 69).YEAR(4) stores a year in 4-digit format. For example, we need to write 19669 to store 1969 as a year. In YEAR (4), the year can be specified from 1901 to 2155.MySQL interprets 2-digit year values with the assistance of following rules:Year values within the vary 00-69 are converted to 2000-2069.Year values in the range 70-99 are converted to 1970-1999.We must not store date values as a 2-digit ...
Read MoreHow can we emulate CHECK CONSTRAINT by using views?
As we know that MySQL supports foreign key for referential integrity but it does not support CHECK constraint. But we can emulate them by using triggers. It can be illustrated with the help of an example given below −ExampleSuppose we have a table named ‘car1’ which can have the fix syntax registration number like two letters, a dash, three digits, a dash, two letters as follows −mysql> Create table car1 (number char(9)); Query OK, 0 rows affected (0.32 sec) mysql> Insert into car1 values('AB-235-YZ'); Query OK, 1 row affected (0.10 sec)The above value is a valid one but what ...
Read MoreHow can we emulate CHECK CONSTRAINT by using MySQL GENERATED COLUMN?
As we know that MySQL supports foreign key for referential integrity but it does not support CHECK constraint. But we can emulate them by using triggers. It can be illustrated with the help of an example given below −ExampleSuppose we have a table named ‘car’ which can have the fix syntax registration number like two letters, a dash, three digits, a dash, two letters as follows −mysql> Create table car2 (number char(9)); Query OK, 0 rows affected (0.32 sec) mysql> Insert into car2 values('AB-235-YZ'); Query OK, 1 row affected (0.10 sec)The above value is a valid one but what ...
Read MoreHow can we emulate CHECK CONSTRAINT by using triggers?
As we know that MySQL supports foreign key for referential integrity but it does not support CHECK constraint. But we can emulate them by using triggers. It can be illustrated with the help of an example given below −ExampleSuppose we have a table named ‘car’ which can have the fix syntax registration number like two letters, a dash, three digits, a dash, two letters as follows −mysql> Create table car (number char(9)); Query OK, 0 rows affected (0.32 sec) mysql> Insert into car values('AB-235-YZ'); Query OK, 1 row affected (0.10 sec)The above value is a valid one but what ...
Read MoreWhat is the difference between MySQL DATETIME and TIMESTAMP data type?
Both the data types store data in “YYYY-MM-DD HH:MM:SS” format and include date as well as time. In spite of these similarities they are having the following differences −Range − Datetime data type supports a date along with time in the range between 1000-01-01 00:00:00 and 9999-12-31 23:59:59. But timestamp data type supports a date along with time in the range between ‘1970-01-01 00:00:01’ to ‘2038-01-19 08:44:07’.Size − Datetime requires 5 bytes along with 3 additional bytes for fractional seconds’ data storing. On the other hand, timestamp datatype requires 4 bytes along with 3 additional bytes for fractional seconds’ data ...
Read MoreHow many DATE data types are supported by MySQL?
MySQL supports following 5 types of DATE data type −DATE - A date is in the range between 1000-01-01 and 9999-12-31. “YYYY-MM-DD” is the default DATE format. For example, January 17th, 1984 would be stored as 1984-01-17.DATETIME − This data type supports a date along with time in the range between 1000-01-01 00:00:00 and 9999-12-31 23:59:59. “YYYY-MM-DD HH:MM:SS” is the default DATETIME format. For example, 2:20 in the afternoon on January 17th, 1984 would be stored as 1984-01-17 14:20:00.TIMESTAMP − A timestamp data type supports a date along with time in the range between ‘1970-01-01 00:00:01’ to ‘2038-01-19 08:44:07’. It ...
Read More