Html web sql database

HTML5 – Web SQL Database
The Web SQL Database API isn't actually part of the HTML5 specification but it is a separate specification
which introduces a set of APIs to manipulate client-side databases using SQL .
I'm assuming you are a great web developer and if that is the case then no doubt, you would be well
aware of SQL and RDBMS concepts. If you still want to have a session with SQL then, you can go through
our SQL Tutorial .
Web SQL Database will work in latest version of Safari, Chrome and Opera.
The Core Methods :
There are following three core methods defined in the spec that I am going to cover in this tutorial -
openDatabase - This method creates the database object either using existing database or creating
new one.
transaction - This method gives us the ability to control a transaction and performing either commit or
rollback based on the situation.
executeSql - This method is used to execute actual SQL query.

Open Database :
The openDatabase method takes care of opening a database if it already
exists, this method will create it if it already does not exist.
To create and open a database, use the following code -
var db = openDatabase('mydb', '1.0', 'Test DB', 2 * 1024 * 1024);
The above method took the following five parameters Database name
Version number Text description
• Size of database
• Creation callback
The last and 5th argument, creation callback will be called if the database is
being created.Without this feature, however, the databases are still being
created on the fly and correctly versioned.

Executing Queries
To execute a query you use the database.transaction() function. This function needs a single
argument, which is a function that takes care of actually executing the query as follows –
The above query will create a table called LOGS in 'mydb' database.
var dbopenDatabase( I mydb' ,' 1 . 0 ' , 'Test DB' , 2 * 1024 * 1024);
db. transaction(function (tx) { tx.executeSq1( 'CREATE TABLE IF
NOT EXISTS LOGS (id unique, log) l ) ;

INSERT Operation
To create enteries into the table we add simple SQL query in the above example as follows –
var db openDatabase( I mydb' , ' 1 . 0 1 , 'Test DB' , 2 * 1024 * 1024);
db. transaction(function (tx) { tx.executeSq1( 'CREATE TABLE IF NOT EXISTS LOGS (id unique, log) ' ) ;
tx.executeSq1( 'INSERT INTO LOGS (id, log) VALUES (1, "foobar") I ) ; tx.executeSq1( 'INSERT INTO
LOGS (id, log) VALUES (2, "logmsg"),);
We can pass dynamic values while creating entering as follows –
var db openDatabase( I mydb' , '1.0 1 'Test DB' , 2 * 1024 * 1024);
db. transaction(function (tx) { tx.executeSq1( 'CREATE TABLE IF NOT EXISTS LOGS (id unique, log) l ) ;
tx.executeSq1( 'INSERT INTO LOGS (id,log) VALUES ( ? , [e_id, e_log]
Here e_id and e_log are external variables, and executeSql maps each item in the array argument to
the "?"s.

READ Operation
To read already existing records we use a callback to capture the results as follows:
db.transaction(function (tx) {
tx.executeSql('CREATE TABLE IF NOT EXISTS LOGS (id unique, log)');
tx.executeSql('INSERT INTO LOGS (id, log) VALUES (1, "foobar")');
tx.executeSql('INSERT INTO LOGS (id, log) VALUES (2, "logmsg")');
});
tx.executeSql('SELECT * FROM LOGS', [], function (tx, results) {
var len = results.rows.length, i;
msg = "<p>Found rows: " + len + "</p>";
document.querySelector('#status').innerHTML += msg;
for (i = 0; i < len; i++) {
alert(results.rows.item(i).log );
}
}, null);
});

Final Example :
So finally, let us keep this example in a full-fledged HTML5 document as follows and try to run it in the
browser :
<!DOCTYPE HTML>
<html>
<head>
<script type = "text/javascript">
var msg;
tx.executeSql('CREATETABLE IF NOT EXISTS LOGS (id unique, log)');
tx.executeSql('INSERT INTO LOGS (id, log)VALUES (1, "foobar")');
tx.executeSql('INSERT INTO LOGS (id, log)VALUES (2, "logmsg")');
msg = '<p>Log message created and row inserted.</p>';
document.querySelector('#status').innerHTML = msg;
})

tx.executeSql('SELECT * FROM LOGS', [], function (tx,
results) {
var len = results.rows.length, i;
msg = "<p>Found rows: " + len + "</p>";
for (i = 0; i < len; i++) {
msg = "<p><b>" + results.rows.item(i).log + "</b></p>";
}
}, null);
});
</script>
</head>
<body>
<div id = "status" name = "status">Status Message</div>
</body>
</html>

This will produce the following result –
Log message created and row inserted.
Found rows: 2
foobar
logmsg

Html web sql database

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