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Object Oriented Programming Articles
Page 569 of 589
How to change the datatype of a column in an existing table using JDBC API?
You can change the datatype of a column in a table using the ALTER TABLE command.SyntaxALTER TABLE Sales MODIFY COLUMN column_name column_new_datatuypeAssume we have a table named Sales in the database with 7 columns namely ProductName, CustomerName, DispatchDate, DeliveryTime, Price, Location and, ID with description as:+--------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName | varchar(255) | YES | | NULL | | | CustomerName | varchar(255) | YES | | NULL ...
Read MoreHow to add a primary key constraint to a column of a table in a database using JDBC API?
You can add a primary key constraint to a column of a table using the ALTER TABLE command.SyntaxALTER TABLE table_name ADD CONSTRAINT MyPrimaryKey PRIMARY KEY (column1, column2...);Assume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:+--------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName | varchar(255) | YES | | NULL | | | CustomerName | varchar(255) | ...
Read MoreHow to drop constraint on a column of a table in a database using JDBC API?
You can drop a constraint on a column of a table using the ALTER TABLE command.SyntaxALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint;Assume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:+--------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName | varchar(255) | YES | UNI | NULL | | | CustomerName | varchar(255) | YES | | NULL | ...
Read MoreThe get() method of AbstractList class in Java
The get() method of the AbstractList class is used to get the element at the specified position in the list. It returns the element at the position set as parameter.The syntax is as follows:public abstract E get(int index)Here, index is the index of the element to return.To work with the AbstractList class, import the following package:import java.util.AbstractList;The following is an example to implement get() method of the AbstractlList class in Java:Exampleimport java.util.LinkedList; import java.util.AbstractList; public class Demo { public static void main(String[] args) { AbstractList myList = new LinkedList(); myList.add(50); ...
Read MoreHow to set auto-increment to an existing column in a table using JDBC API?
You can add/set an auto increment constraint to a column in a table using the ALTER TABLE command.SyntaxALTER TABLE table_name ADD id INT PRIMARY KEY AUTO_INCREMENTAssume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:+--------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName | varchar(255) | YES | UNI | NULL | | | CustomerName | varchar(255) | YES | ...
Read MoreHow to set/insert null values to in to a column of a row using JDBC program?
You can insert null values into a table in SQL in two ways:Directly inserting the value NULL into the desired column as:Insert into SampleTable values (NULL);Using ‘ ’ as nullInsert into SampleTable values (NULL);While inserting data into a table using prepared statement object you can set null values to a column using the setNull() method of the PreparedStatement interface.pstmt.setNull(parameterIndex, sqlType);ExampleAssume we have a table named cricketers_data in the database with the following contents:+------------+------------+---------------+----------------+-------------+ | First_Name | Last_Name | Date_Of_Birth | Place_Of_Birth | Country | +------------+------------+---------------+----------------+-------------+ | Shikhar | Dhawan | 1981-12-05 | ...
Read MoreHow to get the number of records in a table using JDBC?
The ResultSet class doesn’t provide any direct method to get the number of records in a table.The beforeFirst() method navigates the pointer/curser of the ResultSet object to its default position before first.In the same way the last() method positions the cursor at the last row of the ResultSet object.Using these methods you can find the number of records in the current ResultSet object.ExampleAssume we have a table named customers table with contents as shown below:+----+---------+-----+---------+----------------+ | ID | NAME | AGE | SALARY | ADDRESS | +----+---------+-----+---------+----------------+ | 1 | Amit | 25 | 3000.00 ...
Read MoreHow to get the datatype of a column of a table using JDBC?
You can get the datatype of a column of a table using the getColumnType() method of the ResultSetMetaData class.//Retrieving the ResultSetMetaData object ResultSetMetaData rsmd = rs.getMetaData(); //getting the column type String column_name = rsmd.getColumnTypeName(2);Assume we have a table named employee_data in the database with the description as shown below:+----------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | Name | varchar(255) ...
Read MoreHow to get the size of a column of a table using JDBC?
You can get the size of a column of a table using the getPrecision() method of the ResultSetMetaData class.//Retrieving the ResultSetMetaData object ResultSetMetaData rsmd = rs.getMetaData(); //getting the column type int size_name = rsmd. getPrecision(3);Assume we have a table named employee_data in the database with description as shown below:+----------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | Name | varchar(255) | YES | ...
Read MoreHow to delete a row from ResultSet object using JDBC?
The deleteRow() method of the ResultSet interface deletes the current row from the current ResultSet object.//Deleting a column from the ResultSet object rs.deleteRow();Assume we have a table named Cricketers_Data with 6 records as shown below:+----+------------+------------+---------------+----------------+-------------+ | ID | First_Name | Last_Name | Year_Of_Birth | Place_Of_Birth | Country | +----+------------+------------+---------------+----------------+-------------+ | 1 | Shikhar | Dhawan | 1981-12-05 | Delhi | India | | 2 | Jonathan | Trott | 1981-04-22 | CapeTown | SouthAfrica | | 3 ...
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