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MySQL Articles
Page 130 of 355
Is there a naming convention for tables in MySQL?
No, MySQL does not have a preferred naming convention standard. If the name we have chosen is logical and consistent then it would be ok.Two major points need to be remembered, one is that no two tales/databases can have the same name and second we can choose any of the reserved words as the name of table/database.
Read MoreHow to get the first day of the current month in MySQL?
With the help of following MySQL query, we can get the first day of the current month −mysql> SELECT DATE_SUB(LAST_DAY(NOW()),INTERVAL DAY(LAST_DAY(NOW()))- 1 DAY) AS 'FIRST DAY OF CURRENT MONTH'; +----------------------------+ | FIRST DAY OF CURRENT MONTH | +----------------------------+ | 2017-10-01 | +----------------------------+ 1 row in set (0.00 sec)
Read MoreHow will addition, subtraction, multiplication and division operator work with date values stored in MySQL table?
When we try to do such kind of operations with date values stored in the table then MySQL is assuming the date values as the number and perform the arithmetic.Suppose we have a table named ‘example’ having a date value in ‘orderdate’ column then following arithmetic operation will clarify the above −mysql> select * from example; +------------+ | orderdate | +------------+ | 2017-05-25 | +------------+ 1 row in set (0.00 sec) mysql> select orderdate+10 from example; +--------------+ | orderdate+10 | +--------------+ | 20170535 | +--------------+ 1 row in set (0.00 sec) mysql> select orderdate*10 from example; ...
Read MoreHow can I check MySQL tables from a database in accordance with particularncolumn/s name?
The following statement shows the list of two tables having a column ‘email’ in Sample database −mysql> SELECT DISTINCT TABLE_NAME -> FROM INFORMATION_SCHEMA.COLUMNS -> WHERE COLUMN_NAME IN('EMAIL') -> AND TABLE_SCHEMA = 'SAMPLE'; +---------------+ | TABLE_NAME | +---------------+ | employee | | new_student | +---------------+ 2 rows in set (0.04 sec)
Read MoreWhat is the way to check the size of all the MySQL databases?
We can check the size of all MySQL databases with the help of the following statementmysql> SELECT table_schema "Database", -> SUM(data_length + index_length)/1024/1024 "Size in MB" -> FROM information_schema.TABLES GROUP BY table_schema; +--------------------+----------------+ | Database | Size in MB | +--------------------+----------------+ | gaurav | 1.04785156 | | information_schema | 0.00878906 | | mysql | 0.68551350 | | performance_schema | 0.00000000 | | sample | 0.04687500 | | tutorial | 0.03125000 | +--------------------+----------------+ 6 rows in set, 1 warning (0.33 sec)
Read MoreHow MySQL behaves when we use INTERVAL of time unit with CURDATE() function?
As we know that CURDATE() only returns the date unit so it would be ambiguous to use INTERVAL of time unit with CURDATE(). MySQL always represents current date with ‘00:00:00’ time hence when we use INTERVAL of time unit with CURDATE() then such kind of time arithmetic would take this time into consideration. Following examples will clarify it −mysql> Select CURDATE() + INTERVAL 0 hour; +-----------------------------+ | curdate() + Interval 0 hour | +-----------------------------+ | 2017-10-28 00:00:00 | +-----------------------------+ 1 row in set (0.00 sec) mysql> select CURDATE() + INTERVAL 1 hour; +-----------------------------+ | curdate() ...
Read MoreWhy I got output 0(Zero) on converting date like '1965-05-15' to TIMESTAMP?
As we know that with the help of MySQL UNIX_TIMESTAMP function, we can produce the number of seconds from given date/DateTime. But when we try to convert a date like ‘1965-05-15’ it would give 0(Zero) as output because the range of TIMESTAMP is between ‘1970-01-01 00:00:01’ to ‘2038-01-19 08:44:07’. Hence, the date values beyond TIMESTAMP range cannot be converted and will return 0 as output always.Examples are given below −mysql> Select UNIX_TIMESTAMP ('1965-05-15'); +----------------------------------------------+ | unix_timestamp('1965-05-15 05:04:30') | +----------------------------------------------+ | ...
Read MoreHow can we know about the starting range of TIMESTAMP data type with the help of MySQL FROM_UNIXTIME() function?
As we know that this function converts a number of seconds into TIMESTAMP value. So by providing 0 seconds as the argument, it will give us the starting range of TIMESTAMP data type.mysql> Select FROM_UNIXTIME(0); +-------------------------+ | FROM_UNIXTIME(0) | +-------------------------+ | 1970-01-01 05:30:00 | +-------------------------+ 1 row in set (0.00 sec)Now if we will change the argument from 0 to 60 seconds then the time will be changed by 01 minutes.mysql> Select FROM_UNIXTIME(60); +-------------------------+ | FROM_UNIXTIME(60) | +-------------------------+ | 1970-01-01 05:31:00 | +-------------------------+ 1 row in set (0.00 sec)
Read MoreHow does comparison operator work with date values in MySQL?
Comparison operator between dates will work in a logical way. In the following example, while comparing two dates, MySQL is simply comparing two numbers or string −mysql> select 20171027 < 20150825; +---------------------------+ | 20171027 < 20150825 | +---------------------------+ | 0 | +---------------------------+ 1 row in set (0.00 sec)The 0 output shows that the result of the above query is FALSE.mysql> select 20171027 > 20150825; +--------------------------+ | 20171027 > 20150825 | +--------------------------+ | 1 | +--------------------------+ 1 row in set (0.00 sec)The output ‘1’ shows that the result of the above query is TRUE.
Read MoreHow should I display MySQL database that is currently in use?
We can display the name of MySQL database that is currently in use by Select Database() command.mysql> select database(); +------------+ | database() | +------------+ | tutorial | +------------+ 1 row in set (0.00 sec)This command shows that we currently use tutorial database.
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