Difference Between DML and DDL

DML vs. DDL

Data Manipulation Language (also known as DML) is a family of computer languages. They are used by computer programs, and/or database users, to manipulate data in a database – that is, insert, delete and update this data in the database.

Data Definition Language (also known as DDL) is a computer language used to define data structures – as its namesake suggests. It first made its appearance in the CODASYL database model (a model pertaining to the information technology industry consortium, known as Conference on Data Systems Languages). DDL was used within the schema of the database in order to describe the records, fields, and ‘sets’ that made up the user Data Model. It was at first a way in which programmers defined SQL. Now, however, it is used generically to refer to any formal language used to describe data or information structures (for example, XML schemas).

The most popular form of DML is the Structured Query Language (or SQL). This is a language used for databases, and is designed specifically for managing data in relational database management systems (or RDBMS). There are also other forms in which DML is used, for instance – IM S/DLI, CODASYL databases (IDMS, for example), and a few others. DML comprises of SQL data change statements, meaning that stored data is modified, but the schema or database objects remain the same. The functional capability of the DML is organised by the initial word in a statement. This word is most generally a verb – giving the page a specific action to fulfil. There are four specific verbs that initiate an action: SELECT…INTO, INSERT, UPDATE, and DELETE.

The DDL is used mainly to create – that is to make a new database, table, index or stored query. A CREATE statement in SQL literally creates an object inside any RDBMS. As such, the types of objects able to be created are completely dependent on which RDBMS is currently in use. Most RDBMS support the table, index, user, synonym and database creation. In some cases, a system will allow the CREATE command and other DDL commands inside a specific transaction. This means that these functions are capable of being rolled back. The most common CREATE command is the CREATE TABLE command.

DMLs are quite various. They have different functions and capabilities between database vendors. There are only two DML languages, however: Procedural and Declarative. While there are multiple standards established for SQL, most vendors provide their own extensions to the standard without implementing it entirely.

Summary:

1. DML is a grouping of computer languages used by computer programs to manipulate data in a database; DDL is a computer language used specifically to define data structures.

2. The most popular form of DML is SQL, and is comprised of various change statements; DDL mainly uses the CREATE command.

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