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MySQL Articles
Page 303 of 355
Resolve Unknown database in JDBC error with Java-MySQL?\\n
This type of error occurs if you select any database that does not exist in MySQL. Let us first display the error of unknown database in JDBC.The Java code is as follows. Here, we have set the database as ‘onlinebookstore’, which does not exist:import java.sql.Connection; import java.sql.DriverManager; public class UnknownDatabaseDemo { public static void main(String[] args) { String JdbcURL = "jdbc:mysql://localhost:3306/onlinebookstore?useSSL=false"; String Username = "root"; String password = "123456"; Connection con = null; try { con = DriverManager.getConnection(JdbcURL, Username, password); ...
Read MoreHow to add column using alter in MySQL?\\n
Following is the syntax to add column using alter in MySQL:alter table yourTableName add column yourColumnName yourDataType default yourValue;Let us first create a table:mysql> create table alterTableDemo -> ( -> Id int, -> Name varchar(10) -> ); Query OK, 0 rows affected (0.69 sec)Let us check the description of the table using DESC command. This displays Field, Type, Key, etc. of the table:mysql> desc alterTableDemo;This will produce the following output+-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | Id | int(11) | YES ...
Read MoreGet the count of only unique rows in a MySQL column?
In MySQL, COUNT() will display the number of rows. DISTINCT is used to ignore duplicate rows and get the count of only unique rows.Let us first create a table:mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, FirstName varchar(10) ); Query OK, 0 rows affected (0.47 sec)Following is the query to insert some records in the table using insert command:mysql> insert into DemoTable(FirstName) values('Larry'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable(FirstName) values('John'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable(FirstName) values('Sam'); Query OK, 1 row affected (0.13 sec) ...
Read MoreHow to change a primary key in MySQL to auto_increment?\\n
To change a primary key to auto_increment, you can use MODIFY command. Let us first create a table.mysql> create table changePrimaryKeyInAutoIncrement -> ( -> StudentId int not null primary key, -> StudentName varchar(100), -> StudentAge int, -> StudentAddress varchar(100) -> ); Query OK, 0 rows affected (0.63 sec)Let us now check the description of table using desc command:mysql> desc changePrimaryKeyInAutoIncrement;This will produce the following output+----------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------------+--------------+------+-----+---------+-------+ | StudentId | int(11) ...
Read MoreMySQL query to get sum of each column where every column has same number of values?
You can use aggregate function SUM() for this. Let us first create a table −mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, FirstValue int, SecondValue int, ThirdValue int ); Query OK, 0 rows affected (0.57 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(FirstValue, SecondValue, ThirdValue) values(10, 20, 30); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable(FirstValue, SecondValue, ThirdValue) values(60, 50, 40); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable(FirstValue, SecondValue, ThirdValue) values(80, 90, 100); Query OK, 1 row affected ...
Read MoreMySQL query to select one specific row and another random row?\\n
To select one specific row and another random row, you can use ORDER BY and RAND(). Let us first create a sample table:mysql> create table oneSpecificRowAndOtherRandom -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(20) -> ); Query OK, 0 rows affected (0.72 sec)Following is the query to insert some records in the table using insert command:mysql> insert into oneSpecificRowAndOtherRandom(Name) values('Larry'); Query OK, 1 row affected (0.56 sec) mysql> insert into oneSpecificRowAndOtherRandom(Name) values('Sam'); Query OK, 1 row affected (0.13 sec) mysql> insert into oneSpecificRowAndOtherRandom(Name) values('Mike'); Query OK, 1 row affected ...
Read MoreCan I use SUM() with IF() in MySQL?
Yes, you can use SUM() with IF() in MySQL. Let us first create a demo table:mysql> create table DemoTable ( Value int, Value2 int ); Query OK, 0 rows affected (0.51 sec)Following is the query to insert some records in the table using insert command:mysql> insert into DemoTable values(100, 400); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(100, 400); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable values(400, 100); Query OK, 1 row affected (0.14 sec)Following is the query to display records from the table using select command:mysql> select *from DemoTable;This ...
Read MoreHow to use “OR” condition in MySQL CASE expression?\\n
Set the same condition like “OR” in a MySQL CASE expression. Let us first create a sample table.Following is the querymysql> create table caseOrConditionDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(100), -> Score int -> ); Query OK, 0 rows affected (0.49 sec)Following is the query to insert some records in the table using insert command:mysql> insert into caseOrConditionDemo(Name, Score) values('Larry', 85); Query OK, 1 row affected (0.18 sec) mysql> insert into caseOrConditionDemo(Name, Score) values('Sam', 74); Query OK, 1 row affected (0.20 sec) mysql> insert into caseOrConditionDemo(Name, ...
Read MoreDo Double Equal Sign exist in MySQL?
There is no double equal sign concept. It can be used to compare two values. If you use double equal sign(==) in MySQL, you will get an error message.Let us verify the concept is true or not. Declare a variable −mysql> set @Number=10; Query OK, 0 rows affected (0.00 sec)Now, compare the above variable value with 10. If both the values are same then the result will be 1 otherwise 0.Using double equal sign −mysql> select 10==@Number;This will produce the following output i.e. an error −ERROR 1064 (42000): You have an error in your SQL syntax; check the manual ...
Read MoreHow to copy data from one field to another on every row in MySQL?
To copy data from one field to another on every row, use the UPDATE command.Let us first create a table −mysql> create table DemoTable ( StudentId int, StudentFirstName varchar(20), StudentMarks int default 0 ); Query OK, 0 rows affected (0.49 sec)Following is the query to insert records in the table using insert command −mysql> insert into DemoTable(StudentId, StudentFirstName) values(89, 'Larry'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(StudentId, StudentFirstName) values(35, 'Robert'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable(StudentId, StudentFirstName) values(48, 'Chris'); Query OK, 1 row affected (0.13 sec) ...
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