Data Manipulation Language

A data manipulation language (DML) is a family of syntax elements similar to a computer programming language used for inserting, deleting and updating data in a database. Performing read-only queries of data is sometimes also considered a component of DML.

A popular data manipulation language is that of Structured Query Language (SQL), which is used to retrieve and manipulate data in a relational database.^[1] Other forms of DML are those used by IMS/DLI, CODASYL databases, such as IDMS and others.

Data manipulation language comprises the SQL data change statements,^[2] which modify stored data but not the schema or database objects. Manipulation of persistent database objects, e.g., tables or stored procedures, via the SQL schema statements,^[2] rather than the data stored within them, is considered to be part of a separate data definition language. In SQL these two categories are similar in their detailed syntax, data types, expressions etc., but distinct in their overall function.^[2]

Data manipulation languages have their functional capability organized by the initial word in a statement, which is almost always a verb. In the case of SQL, these verbs are:

• SELECT ... FROM ... WHERE ...
• INSERT INTO ... VALUES ...
• UPDATE ... SET ... WHERE ...
• DELETE FROM ... WHERE ...

The purely read-only SELECT query statement is classed with the 'SQL-data' statements^[2] and so is considered by the standard to be outside of DML. The SELECT ... INTO form is considered to be DML because it manipulates (i.e. modifies) data. In common practice though, this distinction is not made and SELECT is widely considered to be part of DML.^[3]

Most SQL database implementations extend their SQL capabilities by providing imperative, i.e., procedural, languages. Examples of these are Oracle's PL/SQL and DB2's SQL PL.

Data manipulation languages tend to have many different flavors and capabilities between database vendors. There have been a number of standards established for SQL by ANSI,^[1] but vendors still provide their own extensions to the standard while not implementing the entire standard.

Data manipulation languages are divided into two types, procedural programming and declarative programming.

Each SQL DML statement is a declarative command. The individual SQL statements are declarative, as opposed to imperative, in that they describe the program's purpose, rather than describing the procedure for accomplishing it.

Data manipulation languages were initially only used within computer programs, but with the advent of SQL have come to be used interactively by database administrators.

See also

• CRUD
• Data definition language
• Data control language
• Query language

References

• "The SQL92 standard". http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt. 

1. ^ ^{a b} SQL92
2. ^ ^{a b c d} SQL92 4.22.2, SQL statements classified by function
3. ^ "Data Manipulation Language Statements". Oracle. http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/sqlplsql.htm#i18503. "Data manipulation language (DML) statements query or manipulate data in existing schema objects."