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The following will describe how to create an open database, create a table, add data, update data, delete data, and delete tables.

Let's introduce three core methods.

1. OpenDatabase: this method creates database objects using an existing database or creating a new database.

2. Transaction: this method allows us to control transaction commit or rollback depending on the situation.

3. ExecuteSql: this method is used to execute a real SQL query.

Step 1: open the connection and create the database

The copy code is as follows:

Var dataBase = openDatabase ("student", "1.0", "Student form", 1024 * 1024, function () {})

If (! dataBase) {

Alert ("Database creation failed!")

} else {

Alert ("Database created successfully!")

}

Explain that the openDatabase method opens an existing database and can also create a database if it does not exist. The meanings of several parameters are:

1, database name.

2, version number is currently 1. 0, regardless of him, write dead OK.

3. Description of the database.

4, set the size of the data.

5, callback function (can be omitted).

The database is created the first time the call is made, and then the connection is established.

The created database exists locally, and the path is as follows:

C:\ Users\ Administrator\ AppData\ Local\ Google\ Chrome\ User Data\ Default\ databases\ http_localhost_4987.

Create a sqllite database, you can use SQLiteSpy to open the file, you can see the data inside. SQLiteSpy is a green software, you can download the address of Baidu or SQLiteSpy official download: SQLiteSpy.

Step 2: create a datasheet

The copy code is as follows:

This.createTable=function () {

DataBase.transaction (function (tx) {

Tx.executeSql (

"create table if not exists stu (id REAL UNIQUE, name TEXT)"

[]

Function (tx,result) {alert ('stu table created successfully');}

Function (tx, error) {alert ('failed to create stu table:' + error.message)

});

});

}

Explain,

The executeSql function has four parameters, which mean:

1) represents the string of the query, and the SQL language used is SQLite 3.6.19.

2) the string data inserted into the query where the question mark is located.

3) callback function executed on success. Returns two parameters: tx and the result of the execution.

4) A callback function that is executed on failure. Returns two parameters: tx and a failed error message.

Step 3: add, delete, modify and check

1) add data:

The copy code is as follows:

This.insert = function () {

DataBase.transaction (function (tx) {

Tx.executeSql (

"insert into stu (id, name) values"

[id,'Xu Mingxiang']

Function () {alert ('data added successfully');}

Function (tx, error) {alert ('failed to add data:' + error.message)

})

});

2) query data

The copy code is as follows:

This.query = function () {

DataBase.transaction (function (tx) {

Tx.executeSql (

"select * from stu", []

Function (tx, result) {/ / callback function executed successfully

/ / do what you want to do to result here.

}

Function (tx, error) {

Alert ('query failed:' + error.message)

})

});

}

Explain

The successful callback function in the above code has an argument result.

Result: the dataset that is queried. Its data type is SQLResultSet, just like DataTable in C #.

SQLResultSet is defined as:

The copy code is as follows:

Interface SQLResultSet {

Readonly attribute long insertId

Readonly attribute long rowsAffected

Readonly attribute SQLResultSetRowList rows

}

The most important attribute, the rows of type SQLResultSetRowList, is the "row" of the dataset.

Rows has two properties: length and item.

Therefore, get the value of a row or column of the query result: result.rows [I] .item [fieldname].

3) Update data

The copy code is as follows:

This.update = function (id, name) {

DataBase.transaction (function (tx) {

Tx.executeSql (

"update stu set name =? where id=?"

[name, id]

Function (tx, result) {

}

Function (tx, error) {

Alert ('update failed:' + error.message)

});

});

}

4) Delete data

The copy code is as follows:

This.del = function (id) {

DataBase.transaction (function (tx) {

Tx.executeSql (

"delete from stu where id=?"

[id]

Function (tx, result) {

}

Function (tx, error) {

Alert ('deletion failed:' + error.message)

});

});

}

5) Delete the data table

The copy code is as follows:

This.dropTable = function () {

DataBase.transaction (function (tx) {

Tx.executeSql ('drop table stu')

});

}

These are all the contents of the article "html Local Database instance Analysis". Thank you for reading! I believe you will gain a lot after reading this article. The editor will update different knowledge for you every day. If you want to learn more knowledge, please pay attention to the industry information channel.

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