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MySQL Articles
Page 300 of 355
Select current time with MySQL now() and convert it to GMT 0?
You can use utc_timestamp() for this. Following is the syntax −SELECT utc_timestamp();Let us check the current time using now().Following is the query −mysql> select now();This will produce the following output −+---------------------+ | now() | +---------------------+ | 2019-04-11 17:50:05 | +---------------------+ 1 row in set (0.00 sec)Following is the query to get GMT 0 −mysql> SELECT utc_timestamp();This will produce the following output −+---------------------+ | utc_timestamp() | +---------------------+ | 2019-04-11 12:20:08 | +---------------------+ 1 row in set (0.00 sec)
Read MoreHow to check if a table exists in MySQL and create if it does not already exist?
If you try to create a table and the table name already exist then MySQL will give a warning message. Let us verify the concept.Here, we are creating a table that already exist −mysql> CREATE TABLE IF NOT EXISTS DemoTable ( CustomerId int, CustomerName varchar(30), CustomerAge int ); Query OK, 0 rows affected, 1 warning (0.05 sec)The table name DemoTable is already present. Let us check the warning message.Following is the query −mysql> show warnings;This will produce the following output i.e. the warning message −+-------+------+------------------------------------+ | Level | Code | Message ...
Read MoreGet the average row length of a MySQL table
In order to get the average row length of a table in MySQL, you can use INFORMATION_SCHEMA.TABLES. Let us first create a table. Following is the query −mysql> create table Client_information -> ( -> Id int, -> Name varchar(10) -> ); Query OK, 0 rows affected (0.48 sec)Following is the query to insert some records in the table using insert command −mysql> insert into Client_information values(1, 'Larry'); Query OK, 1 row affected (0.14 sec) mysql> insert into Client_information values(2, 'Mike'); Query OK, 1 row affected (0.17 sec) mysql> insert into Client_information values(3, 'Sam'); Query ...
Read MoreIs it possible to divide records in both ascending and descending order in MySQL and display them alternatively?
Yes, you can perform this in MySQL by first getting the middle value. Let us first create a table:mysql> create table DemoTable ( UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY ); Query OK, 0 rows affected (0.65 sec)Following is the query to insert some records in the table using insert command:mysql> insert into DemoTable values(); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable values(); Query OK, 1 row affected (0.16 sec) mysql> ...
Read MoreHow to form a composite key to be unique in MySQL?
To form a composite key to be unique, you need to use ADD UNIQUE command. Following is the syntax −alter table yourTableName add unique yourUniqueName( yourColumnName1, yourColumnName2, .......N);Let us first create a table. Following is the query −mysql> create table makeCompositeKeyDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(40), -> StudentAge int, -> StudentGrade char(1) -> ); Query OK, 0 rows affected (2.34 sec)Now check the description of the table using DESC command. Following is the query −mysql> desc makeCompositeKeyDemo;This will produce the following output −+--------------+-------------+------+-----+---------+----------------+ | Field ...
Read MoreDrop a MySQL Table after x hours?
You need to create event to drop table after x hours. The syntax is as follows −CREATE EVENT yourEventName ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL x HOUR DO DROP TABLE IF EXISTS yourTableName;Let us first create a table −mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudnetFirstName varchar(20), StudentLastName varchar(20), StudnetAge int ); Query OK, 0 rows affected (0.52 sec)Now implement the above event in order to drop table after 2 hours −mysql> CREATE EVENT drop_table_event_after2HoursDemo ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 2 HOUR DO DROP TABLE IF EXISTS DemoTable; Query OK, ...
Read MoreHow to display some columns (not all) in MySQL?
In order to show some columns, use NOT IN and set those columns which you do not want to display. Let us first create a table. Following is the query −mysql> create table student_Information -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(50), -> StudentAge int, -> StudentAddress varchar(100), -> StudentAllSubjectScore int -> ); Query OK, 0 rows affected (0.69 sec)Following is the query to display a description about the above table −mysql> desc student_Information;This will produce the following output −+------------------------+--------------+------+-----+---------+----------------+ | Field ...
Read MoreCounting number of positive and negative votes in MySQL?
To count number of positive and negative votes, you can use CASE statement along with aggregate function SUM().Let us first create a table −mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Vote int ); Query OK, 0 rows affected (1.70 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(Vote) values(-10); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable(Vote) values(100); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(Vote) values(45); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(Vote) values(-6); Query OK, 1 row ...
Read MoreCheck that a table exists in MySQL?
In order to check a table exists in MySQL, you can use INFORMATION_SCHEMA.TABLES. Let us first create a table −mysql> create table Client_information -> ( -> Id int, -> Name varchar(10) -> ); Query OK, 0 rows affected (0.48 sec)Following is the query to insert some records in the table using insert command −mysql> insert into Client_information values(1, 'Larry'); Query OK, 1 row affected (0.14 sec) mysql> insert into Client_information values(2, 'Mike'); Query OK, 1 row affected (0.17 sec) mysql> insert into Client_information values(3, 'Sam'); Query OK, 1 row affected (0.19 sec)Following is the ...
Read MoreHow to set default date time as system date time in MySQL?
You can use CURRENT_TIMESTAMP to set system date time. Let us first create a table −mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, ClientFirstName varchar(20), ClientLastName varchar(20), ClientAge int ); Query OK, 0 rows affected (0.66 sec)Following is the query to set default datetime as system date time in MySQL −mysql> alter table DemoTable add column ClientProjectDeadline timestamp default current_timestamp; Query OK, 0 rows affected (0.46 sec) Records: 0 Duplicates: 0 Warnings: 0Let us check the description of table once again −mysql> desc DemoTable;This will produce the following output −+-----------------------+-------------+------+-----+-------------------+----------------+ | Field ...
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