Database must be known in SQL four languages: DDL DML DCL TCL

Today in the group discussion, DDL or DML, I this small white or summed up their differences.

1. Ddl–data Definition Language

Database Definition language: Defines the structure of the database.

The main orders are Create,alter,drop, and so on, the following examples are detailed. This language does not require a commit, so be cautious.

Create–to create objects in the database creating objects

Example: CREATE DATABASE test; To create a database named Test

Alter–alters the structure of the database structure

Example: ALTER TABLE test ADD birthday date; Modify test table to add Birthday column of date type

Drop–delete objects from the database to delete objects from databases

Example: Drop database test;//Delete test databases

There are other:

truncate– TRUNCATE TABLE content (development period, still quite common)

comment– adding notes to a data dictionary

2. Dml–data Manipulation Language

Database manipulation Language: processing data in a database in SQL

Its main orders have Select,insert,update,delete, and so on, these examples are often not introduced. The language requires a commit. There are also commonly used lock TABLE, remember to write a locked blog – portal

There are other unfamiliar:

call– call a PL/SQL or Java subroutine
EXPLAIN plan– Parse Data access path

3. Dcl–data Control Language

Database Control Language: Authorization, role control, etc.

grant– granting access to users

revoke– Revoke authorization rights

4. Tcl–transaction Control Language

Transaction Control Language

commit– saving the work that has been done

savepoint– setting a savepoint in a transaction can be rolled back here

rollback– rollback

SET transaction– Change transaction options

Database must be known in SQL four languages: DDL DML DCL TCL (EXT)