Web SQL database usage tutorial

The Web SQL Database API is not part of the HTML5 specification, but it is an independent specification that introduces a set of APIs for using SQL to operate client databases.

Core method

openDatabase-create a database object using an existing database or a new database

transaction-can control a thing, and based on In this case, execute commit or rollback

executeSql-Execute the actual SQL statement

Open the database

//用openDatabase()方法打开已存在的数据库，如果数据库不存在，则会创建一个新的数据库var db = openDatabase('mydb', '1.0', 'Test DB', 2 * 1024 * 1024);

openDatabase( ) Description of the five parameters corresponding to the method:

1. Database name

2. Version number

3. Description Text

4. Database size (bytes)

5. Create callback (optional)

Five parameters, the creation callback will be called after the database is created.

Create table

var db = openDatabase('mydb', '1.0', 'Test DB', 2 * 1024 * 1024);
db.transaction(function (tx) {  
   tx.executeSql('CREATE TABLE IF NOT EXISTS LOGS (id unique, log)');
});

Insert data

var db = openDatabase('mydb', '1.0', 'Test DB', 2 * 1024 * 1024);
db.transaction(function (tx) {
   tx.executeSql('CREATE TABLE IF NOT EXISTS LOGS (id unique, log)');
   tx.executeSql('INSERT INTO LOGS (id, log) VALUES (1, "博客园")');
   tx.executeSql('INSERT INTO LOGS (id, log) VALUES (2, "www.cnblogs.com")');
});

Also Inserting data using dynamic values

 db = openDatabase(, , ,  *  *

Reading data

var db = openDatabase('mydb', '1.0', 'Test DB', 2 * 1024 * 1024);
 
db.transaction(function (tx) {
   tx.executeSql('CREATE TABLE IF NOT EXISTS LOGS (id unique, log)');
   tx.executeSql('INSERT INTO LOGS (id, log) VALUES (1, "博客园")');
   tx.executeSql('INSERT INTO LOGS (id, log) VALUES (2, "www.cnblogs.com")');
});
 
db.transaction(function (tx) {
   tx.executeSql('SELECT * FROM LOGS', [], function (tx, results) {      var len = results.rows.length;
      msg = "<p>查询记录条数: " + len + "</p>";
      document.querySelector('#status').innerHTML +=  msg;    
      for (i = 0; i < len; i++){
          msg = "<p><b>" + results.rows[i].log + "</b></p>";
      }
    
   }, null);
});

Deleting records

db.transaction(function (tx) {
    tx.executeSql('DELETE FROM LOGS  WHERE id=1');
});

Deleting data can also be dynamic

db.transaction(function(tx) {
    tx.executeSql('DELETE FROM LOGS WHERE id=?', [id]);
});

Update records

tx.executeSql("UPDATE CC SET logname='www.baidu.com' WHERE id=2");

Updated data can also be dynamic

tx.executeSql("UPDATE CC SET logname='www.baidu.com' WHERE id=?", [id]);

Note: Delete and modify cannot be placed in the same executeSql as the table creation statement. It is best to write them separately

The following is the built database

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