Database Articles - Page 265 of 671

To swap two values in a column, use CASE WHEN statement. Let us first create a table −mysql> create table DemoTable1382    -> (    -> StudentName varchar(20)    -> ); Query OK, 0 rows affected (0.57 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1382 values('John'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1382 values('Chris'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1382 values('Adam'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1382 values('Bob'); Query OK, 1 row affected (0.17 sec)Display all records from the table using ... Read More

For maximum value, use MAX() along with CAST() for conversion. Since we want maximum value from string-numbers beginning with specific characters, use RLIKE. Let us first create a table −mysql> create table DemoTable1381    -> (    -> DepartmentId varchar(40)    -> ); Query OK, 0 rows affected (0.48 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1381 values('IT794'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable1381 values('AT1034'); Query OK, 1 row affected (0.52 sec) mysql> insert into DemoTable1381 values('IT967'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1381 values('IT874'); Query ... Read More

Let us first create a table −mysql> create table DemoTable1    -> (    -> StudentId int,    -> StudentName varchar(20)    -> ); Query OK, 0 rows affected (1.24 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1 values(210, 'Adam'); Query OK, 1 row affected (0.11 sec)Display all records from the table using select statement −mysql> select * from DemoTable1;This will produce the following output −+-----------+-------------+ | StudentId | StudentName | +-----------+-------------+ |       210 | Adam        | +-----------+-------------+ 1 row in set (0.00 sec)Here is the query to create ... Read More

To view cascades, use SHOW CREATE TABLE in MySQL. Let us first create a table −mysql> create table DemoTable1378    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> EmployeeId varchar(20),    -> EmployeeFirstName varchar(20),    -> EmployeeLastName varchar(20),    -> EmployeeCountryName varchar(40),    -> EmployeeAge int,    -> EmployeeSalary int,    -> UNIQUE(EmployeeFirstName, EmployeeSalary),    -> INDEX First_Last_NameIndex(EmployeeFirstName, EmployeeLastName)    -> ); Query OK, 0 rows affected (0.93 sec)Let us now view cascades in MySQL −mysql> show create table DemoTable1378;This will produce the following output −+---------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table         | Create Table ... Read More

For this, use INTERVAL in MySQL. Let us first create a table −mysql> create table DemoTable1376    -> (    -> AdmissionDate date    -> ); Query OK, 0 rows affected (0.68 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1376 values('2018-01-21'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1376 values('2017-12-01'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1376 values('2018-11-02'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable1376 values('2019-03-14'); Query OK, 1 row affected (0.17 sec)Display all records from the table using select statement−mysql> select * from ... Read More

The EXPLAIN keyword tells how MySQL executes the query. Let us first create a table −mysql> create table DemoTable1375    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> FirstName varchar(20),    -> INDEX FIRST_INDEX(FirstName)    -> ); Query OK, 0 rows affected (0.73 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1375(FirstName) values('Chris'); Query OK, 1 row affected (0.25 sec) mysql> insert into DemoTable1375(FirstName) values('Bob'); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable1375(FirstName) values('Sam'); Query OK, 1 row affected (1.06 sec) mysql> insert into DemoTable1375(FirstName) values('David'); Query OK, ... Read More

Use CASE WHEN for this in MySQL and set CASE condition inside the COUNT() method to count. Let us first create a table −mysql> create table DemoTable1374    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> Name varchar(20),    -> Score int    -> ); Query OK, 0 rows affected (0.61 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1374(Name, Score) values('Chris', 45); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable1374(Name, Score) values('David', 78); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1374(Name, Score) values('Bob', 45); ... Read More

To display records like JSON format, use MySQL concat(). Let us first create a table −mysql> create table DemoTable1373    -> (    -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> StudentDetails text    -> ); Query OK, 0 rows affected (0.86 sec)Insert some records in the table using insert command. Here, we haven’t inserted anything −mysql> insert into DemoTable1373 values(); Query OK, 1 row affected (0.27 sec) mysql> insert into DemoTable1373 values(); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable1373 values(); Query OK, 1 row affected (0.18 sec)Display all records from the table using ... Read More

For this, just update the table and subtract. Let us first create a table −mysql> create table DemoTable1372    -> (    -> Value int    -> ); Query OK, 0 rows affected (0.77 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1372 values(500); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable1372 values(100); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable1372 values(900); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable1372 values(1000); Query OK, 1 row affected (0.32 sec)Display all records from the table using select statement −mysql> ... Read More

For this, use GROUP_CONCAT(). Do not use GROUP BY clause, since GROUP_CONTACT() is a better and quick solution.Let us first create a table −mysql> create table DemoTable1371    -> (    -> Id int,    -> CountryName varchar(40)    -> ); Query OK, 0 rows affected (0.89 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1371 values(100, 'US'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable1371 values(100, 'UK'); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable1371 values(101, 'AUS'); Query OK, 1 row affected (0.27 sec) mysql> insert into DemoTable1371 values(101, ... Read More