Android SQLite database summary

sqlite

SQLite is an ultra lightweight embedded database with a size of only a few hundred KB. However, its syntax supports the standard SQL syntax and follows the acid transaction of the database. Therefore, it is easy for developers who have studied other databases to master its use.

SQL syntax will not be introduced. Let's look directly at the use in Android

Sqliteopenhelper - encapsulated database operation auxiliary class, which needs to be rewritten

override method

Oncreate: initialize the database, create tables, and add initial data

Onupgrade: database operations during database version upgrade, such as backup and database deletion

common method

Getreadabledatabase() gets the sqlitedatabase object and operates the database

Getwritabledatabase() gets sqlitedatabase object and operates the database

Difference: when the disk space is full or not writable, method 1 will obtain the read-only database object, while method 2 will report an error. Under normal circumstances, all the obtained database objects are read-write.

Creating an Android database requires creating objects

Create a database class object in the activity class

After creating the data object, you can manipulate the data. The difference between the two methods has been mentioned above

Sqlitedatabase provides us with many methods to manipulate data

Delete: (int) delete (string table, string whereclause, string [] whereargs)

Table: table name

Where clause: where conditional column name placeholder id =?

Whereargs: parameter value array

Add: (long) insert (string table, string nullcolumnhack, contentvalues)

Nullcolumnhack: null column

Contentvalues values: store the added data through key value pairs. Key is the column value and value is the value

The bottom layer of the insert method is by splicing strings. If the content values are empty, the spliced SQL statement will report an error if it cannot be executed. Therefore, give a column that can be empty. When the content values are empty, it can also be executed. If you are interested, you can take a look at the source code

Update: (int) update (string table, contentvalues, string [] whereargs)

The meaning of the parameter is the same as above

Query: (cursor) query (Boolean distinct, string table, string [] columns, string selection, string [] selectionargs, string groupby, string having, string orderby, string limit)

The return value is a cursor. For simple queries with many query parameters, it is easier to write an SQL statement

Boolean distinct de duplication

String table table name

String [] columns column to query

String selection query criteria

String [] selectionargs query parameter value

String groupby grouping

String having grouping condition

String orderby sort

String limit paging query limit

Close database: (void) close()

Execute an SQL statement: (void) execsql (string SQL) add, delete, modify and query

Query SQL: (cursor) rawquery (string SQL, string [] selectionargs)

affair

Paste code to execute SQL statements and encapsulated methods

query

If you can't use parameters, just leave them empty. Just traverse the data and use the while loop

Cursor c = db.query("student",null);// Query and get cursor

to update

delete

increase

The above is the whole content of this article. I hope the content of this article can bring some help to your study or work. At the same time, I also hope to support a lot of programming tips!