Business, the concept of DML,DDL,DCL

1. The transaction

The official interpretation of the matter is: a transaction is a logical unit that contains one or more SQL statements. The SQL statements in a transaction can be either uncommitted (commit) or not rolled back (Rollback). From the above explanation, a transaction is similar to a process in an operating system, indivisible when executed, or submitted together, Either rolling back together, the transaction can be understood as an interaction with the Oracle server, and there are many types of transactions in Oracle, including read-write transactions, readable transactions, discrete transactions. The default is read-write transactions.

※ Read and Write transactions: Transactions can include queries, inserts, updates, and deletes table records of the SQL statement, that is, can contain the statement to change the database.

※ Read-only transaction: As implies, the transaction cannot contain statements that alter the database, only the database cannot write.

※ Logical transactions: Mainly used to improve the performance of the database, in discrete transactions in a number of time-consuming operations together to execute.

2.DML

The database divides the SQL statements into three categories: DML statements, DDL statements, DCL statements

The Database maintenance language (data manipulation Language or data modification LANGUAGE,DML) includes select,insert,update,delete statements, and the latter three are used to change the data in the table. DML statements are used to manipulate table data.

3.DDL

Data definition Language (LANGUAGE,DDL), which refers to the language in which database objects are created, modified, and deleted, and the corresponding statements are create,alter,drop.

4.DCL

The database control language, Data Control Language, DCL, which controls user access to the database. The common three commands are grant,revoke,set role.