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MySQL Articles
Page 283 of 355
What are the advantages and limitations of JDBC PreparedStatement?
Following are the advantages of the prepared statement:By avoiding multiple compilation and execution of statements, prepared statements perform faster.Using prepared statements, we can insert values to advanced datatypes such as BLOB, CLOB, OBJECT easily with the help of the setter methods provided by the PreparedStatement interface.By providing setter method to set values prepared statement avoids the use of quotes and other special characters with in the query, and thereby it escapes the SQL injection attacksFollowing are the limitations of prepared statements:Since a PreparedStatement object represents only one SQL statement at a time, we can execute only one statement by one ...
Read MoreCount multiple occurrences of separate texts in MySQL?
You can use aggregate function count along with if() for this. To understand the concept, let us create a table. The query to create a table is as followsmysql> create table CountOccurrencesDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> TechnicalSubject varchar(100) -> ); Query OK, 0 rows affected (0.68 sec)Now you can insert some records in the table using insert command. The query is as followsmysql> insert into CountOccurrencesDemo(TechnicalSubject) values('Java'); Query OK, 1 row affected (0.14 sec) mysql> insert into CountOccurrencesDemo(TechnicalSubject) values('MongoDB'); Query OK, 1 row affected (0.13 sec) mysql> insert into ...
Read MoreWhat is ResultSetMetaData in JDBC? What is its significance?
The ResultSetMetaData provides information about the obtained ResultSet object like, the number of columns, names of the columns, datatypes of the columns, name of the table etc…Following are some methods of ResultSetMetaData class.MethodDescriptiongetColumnCount()Retrieves the number of columns in the current ResultSet object.getColumnLabel()Retrieves the suggested name of the column for use.getColumnName()Retrieves the name of the column.getTableName()Retrieves the name of the table.Exampleimport java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.Statement; public class ResultSetMetadataExample { public static void main(String args[]) throws Exception { //Registering the Driver DriverManager.registerDriver(new com.mysql.jdbc.Driver()); //Getting the connection ...
Read MoreWhat is the difference between execute(), executeQuery() and executeUpdate() methods in JDBC?
Once you have created the statement object you can execute it using one of the execute methods of the Statement interface namely, execute(), executeUpdate() and, executeQuery().The execute() method: This method is used to execute SQL DDL statements, it returns a boolean value specifying weather the ResultSet object can be retrieved.Exampleimport java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.Statement; public class Example { public static void main(String args[]) throws SQLException { //Registering the Driver DriverManager.registerDriver(new com.mysql.jdbc.Driver()); //Getting the connection String mysqlUrl = "jdbc:mysql://localhost/sampleDB"; Connection con = ...
Read MoreWhy are Prepared Statements in JDBC faster than Statements? Explain?
While executing statements using Statement object, especially insert statements, each time a query is executed the whole statement is compiled and executed again and again where, the only difference among these statements is the values of the statements.Whereas, prepared statement is a precompiled statement i.e. the query is compiled and stored in the database, using place holders (?) instead of values and values to these place holders are supplied later.Thus, avoiding unnecessary compilation and execution of the statement again and again.ExampleSuppose, we have a table named Dataset in the database with the columns mobile_brand and unit_sale, if we want to ...
Read MoreHow many locking systems are there in JDBC?
You can lock a record, set of records, database table, table-space etc. and when we do we cannot change the locked values. Following are the types of locking in JDBC:Row and Key Locks: These are used to lock a particular row. Using these locks, you can achieve concurrency.Page Locks: These are used to lock a page. If you apply this, whenever the contents of a row changes, the database locks the entire page which holds the row. If you need to update/change large number of rows at once you can use this lock.Table Locks: You can lock a table using ...
Read MoreWhat are the important methods of the SQLException class?
An SQLException can occur both in the driver and the database. When such an exception occurs, an object of type SQLException will be passed to the catch clause.The passed SQLException object has the following methods available for retrieving additional information about the exception:MethodDescriptiongetErrorCode( )Gets the error number associated with the exception.getMessage( )Gets the JDBC driver's error message for an error, handled by the driver or gets the Oracle error number and message for a database error.getSQLState( )Gets the XOPEN SQLstate string. For a JDBC driver error, no useful information is returned from this method. For a database error, the five-digit ...
Read MoreCan we call functions using Callable Statements? Explain with an example in JDBC?
Like procedures, you can also create function in a database and store them.SyntaxFollowing is the syntax of creating a function in a(MySQL) database:CREATE FUNCTION Function_Name(input_arguments) RETURNS output_parameter BEGIN declare variables; statements . . . . . . . . . . return data_type; ENDExampleSuppose we have a table named Emp in the database with the following content:+--------+------------+----------------+ | Name | DOB | Location | +--------+------------+----------------+ | Amit | 1970-01-08 | Hyderabad | | Sumith | 1970-01-08 | Vishakhapatnam | | Sudha | 1970-01-05 | Vijayawada ...
Read MoreWhat is JDBC SQL Escape Syntax Explain?
The escape syntax gives you the flexibility to use database specific features unavailable to you by using standard JDBC methods and properties.The general SQL escape syntax format is as follow:{keyword 'parameters'}Following are various escape syntaxes in JDBC:d, t, ts Keywords: They help identify date, time, and timestamp literals. As you know, no two DBMSs represent time and date the same way. This escape syntax tells the driver to render the date or time in the target database's format{d 'yyyy-mm-dd'}Where yyyy = year, mm = month; dd = date. Using this syntax {d '2009-09-03'} is March 9, 2009.Example//Create a Statement object ...
Read MoreWhat is DatabaseMetaData in JDBC? What is its significance?
Generally, Data about data is known as metadata. The DatabaseMetaData interface provides methods to get information about the database you have connected with like, database name, database driver version, maximum column length etc...Following are some methods of DatabaseMetaData class.MethodDescriptiongetDriverName()Retrieves the name of the current JDBC drivergetDriverVersion()Retrieves the version of the current JDBC drivergetUserName()Retrieves the user name.getDatabaseProductName()Retrieves the name of the current database.getDatabaseProductVersion()Retrieves the version of the current database.getNumericFunctions()Retrieves the list of the numeric functions available with this database.getStringFunctions()Retrieves the list of the numeric functions available with this database.getSystemFunctions()Retrieves the list of the system functions available with this database.getTimeDateFunctions()Retrieves the list ...
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