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Database Articles
Page 347 of 547
Select maximum of sum of two columns in MySQL
To select maximum of sum of two columns, use aggregate function MAX() along with subquery. Let us first create a table −mysql> create table DemoTable1587 -> ( -> Value1 int, -> Value2 int -> ); Query OK, 0 rows affected (0.59 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1587 values(30, 50); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable1587 values(80, 90); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1587 values(40, 67); Query OK, 1 row affected (0.13 sec)Display all records from the table using select ...
Read MoreDisplay information about field names in MySQL including TYPE, KEY, etc.
To display information about field names, the syntax is as follows −show columns from yourTableName;Let us first create a table −mysql> create table DemoTable1586 -> ( -> EmployeeId int, -> EmployeeFirstName varchar(20), -> EmployeeLastName varchar(20), -> EmployeeAge int, -> EmployeeCountryName varchar(20), -> EmployeeSalary int -> ); Query OK, 0 rows affected (0.78 sec)Following is the query to display field names −mysql> show columns from DemoTable1586;This will produce the following output −+---------------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | ...
Read MoreWhat will happen if we have set UNIQUE and multiple insertion with duplicate values
An error will arise and nothing will get inserted in the table Let us see an example and create a table −mysql> create table DemoTable1585 -> ( -> StudentId int, -> StudentMarks int, -> UNIQUE(StudentId) -> ); Query OK, 0 rows affected (1.02 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1585 values(1,87),(2,98),(3,91),(3,48); ERROR 1062 (23000): Duplicate entry '3' for key 'StudentId'Display all records from the table using select statement −mysql> select * from DemoTable1585;This will produce the following output. Nothing gets inserted:Empty set (0.00 sec)
Read MoreDeleting partial data from a field in MySQL?
To delete partial data, use UPDATE command along with REPLACE(). Let us first create a table −mysql> create table DemoTable1583 -> ( -> GameDetails text -> ); Query OK, 0 rows affected (1.38 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1583 values('=Candy, 2000'); Query OK, 1 row affected (0.53 sec) mysql> insert into DemoTable1583 values('=Lucky29, 10000'); Query OK, 1 row affected (0.25 sec)Display all records from the table using select statement −mysql> select * from DemoTable1583;This will produce the following output −+------------------------------------------------------------+ | GameDetails ...
Read MoreQuery MySQL table and fetch rows posted before the last 3 days?
Let’s say the current date is −'2019-10-20We will first see an example and create a table −mysql> create table DemoTable1582 -> ( -> PostedDate datetime -> ); Query OK, 0 rows affected (13.36 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1582 values('2019-01-21 12:34:40'); Query OK, 1 row affected (1.06 sec) mysql> insert into DemoTable1582 values('2019-10-15 11:00:00'); Query OK, 1 row affected (0.87 sec) mysql> insert into DemoTable1582 values('2019-10-25 1:10:00'); Query OK, 1 row affected (1.14 sec)Display all records from the table using select statement −mysql> select * from DemoTable1582;This will produce the ...
Read MoreHow to ensure that MySQL rows are unique?
To ensure that MySQL rows are unique, you need to use UNIQUE constraint. Let us first create a table −mysql> create table DemoTable1580 -> ( -> id int, -> Name varchar(20), -> Age int -> ); Query OK, 0 rows affected (0.73 sec)Here is the query to create unique constraints to ensure MySQL rows are unique −mysql> alter table DemoTable1580 add unique index(id, Name, Age); Query OK, 0 rows affected (0.45 sec) Records: 0 Duplicates: 0 Warnings: 0Insert some records in the table using insert command −mysql> insert into DemoTable1580 values(101, 'Chris', 21); Query OK, ...
Read MoreMySQL select and insert in two tables with a single query
Here is the query to create first table.mysql> create table DemoTable1 -> ( -> StudentName varchar(20), -> StudentMarks int -> ); Query OK, 0 rows affected (0.67 sec)To understand the above concept, let us create second table.mysql> create table DemoTable2 -> ( -> Name varchar(20) -> ); Query OK, 0 rows affected (0.61 sec)Insert some records in the table using insert command −mysql> insert into DemoTable2 values('Chris'); Query OK, 1 row affected (0.12 sec)Display all records from the table using select statement −mysql> select * from DemoTable2;This will produce the following output −+-------+ ...
Read MoreEasiest way to get number of rows in a MySQL table?
The easiest way to get number of rows, use aggregate function COUNT(*). Let us first create a table −mysql> create table DemoTable1575 -> ( -> FirstName varchar(20) -> ); Query OK, 0 rows affected (1.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1575 values('Chris'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1575 values('Bob'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1575 values('Adam'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable1575 values('Robert'); Query OK, 1 row affected (0.15 sec)Display all records from the table ...
Read MoreMySQL query to replace special characters from column value
Let us first create a table −mysql> create table DemoTable1574 -> ( -> StudentCode varchar(20) -> ); Query OK, 0 rows affected (0.59 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1574 values('111_Carol'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable1574 values('______'); Query OK, 1 row affected (0.30 sec) mysql> insert into DemoTable1574 values('David_12345'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable1574 values('______'); Query OK, 1 row affected (0.12 sec)Display all records from the table using select statement −mysql> select * from DemoTable1574;This will produce the following ...
Read MoreHow to order or choose rows in MySQL GROUP BY clause?
Let us first create a table −mysql> create table DemoTable1572 -> ( -> StudentId int, -> StudentMarks int, -> StudentName varchar(20) -> ); Query OK, 0 rows affected (0.56 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1572 values(1, 79, 'Sam'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1572 values(2, 89, 'Chris'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1572 values(3, 98, 'David'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable1572 values(4, 79, 'Bob'); Query OK, 1 row affected (0.10 sec)Display all ...
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