The difference between the DML,DDL,DCL,DQL

Dml

English abbreviation

DML = Data manipulation Language, a command that enables users to query a database and manipulate the computer language of data in an existing database. Specifically, update update, insert INSERT, delete deletion.

DML = Data Media Laboratory, lab.

DML = Doctor of Modern Languages, PhD in modern languages.

DML (datamanipulation Language) Data manipulation language, one of the SQL classifications, in addition to the DDL (datadefinition Language) data definition language and DCL (DataControl Language) Data Control language. DML includes: INSERT, UPDATE, DELETE. Note that the SELECT statement belongs to DQL (DataQuery Language). 1

DML:abbr.Doctorof Modern Languages Modern language doctor

Classification

DML is divided into two classes of interactive DML and embedded DML.

Depending on the level of the language, DML can be divided into two kinds of procedural and non procedural DML.

such as Insert,delete,update,select (INSERT, delete, modify, retrieve) are DML.

Interactive DML: This type of DML is a self-contained system that can operate directly on a terminal.

Inline DML: This type of DML is embedded in the main language. At this point the main language is a language that expands to handle DML statements.

Procedural DML: When users are programming, they need to not only point out what to do (what data is needed), but also how to do it (how to get the data). Layered, reticulate DML belongs to the procedural language.

Non-procedural DML: When you are programming, you only need to point out "what to do" and you don't need to point out "how". Relational DML belongs to a non procedural language.

DDL

The database Schema definition language DDL (datadefinition Language) is the language used to describe the real-world entities to be stored in the database. A database schema contains descriptive definitions for all entities in the database. These definitions include the structure definition, the operation method definition, and so on.

The database schema definition language is not a programming language, and the DDL database schema definition language is an integral part of the SQL language (Structured programming language). The SQL language includes three main programming language categories of statements: Data definition language (DDL), Data Manipulation language (DML), and Data Control Language (DCL).

The pattern of DDL description, which must be compiled by computer software and converted into a format convenient for computer storage, querying and manipulating, is called a schema compiler.

Schema compiler processing pattern definitions mainly produce two types of data: data dictionary and data type and structure definition.

The data dictionary and the internal structure information of the database are the basis of creating the database corresponding to the pattern, based on which the logical structure of each database is created; Access to database data, queries based on schema information determine the way and type of data access, and the relationship between data and the integrity of data constraints.

A data dictionary is a representation of the internal information of a pattern, and the data dictionary is stored differently from different DBMS.

The definition of data type and structure means that when an application is connected to a database, the application needs to understand the data types and structures that are generated and extracted. is the data type and structure definition of the user workspace that is provided for the various host languages, which is consistent with the logical structure of the user workspace and the database, and reduces the data conversion process, which is typically defined with a single header file.

There are usually two ways to define a database schema: interactively define patterns and describe text definition patterns through Data Description Language DDL.

DCL

DCL (DataControl Language) is a database control language. is a statement that sets or changes permissions for a database user or role, including (Grant,deny,revoke, and so on) statements. In the default state, only people like Sysadmin,dbcreator,db_owner or db_securityadmin have the power to execute DCL

DCL Database Control language differs from the programming language, and the components of SQL language (Structured programming language) include the DCL Database control language. The SQL language includes three main programming language categories of statements: Data definition language (DDL), Data Manipulation language (DML), and Data Control Language (DCL).

Second, (DCL) composite lever

Compound lever (Degree of combining leverage) refers to the leverage effect of the change rate of common shares per share, which is caused by the existence of fixed cost and fixed financial cost, which is greater than that of production and sales.

The main index of the compound lever measure is the compound lever coefficient or the compound lever degree. The compound lever coefficient refers to the multiple of the change rate of common stock per share. Its calculation formula is:

Dcl= (eps/eps) (q/q) =DOLXDFL

Compound lever coefficient = base period marginal contribution (base period tax before profit-interest)

DQL

Dql:data querylanguage SELECT Data Query Language

Select specific usage

Selectselect_list

[Intonew_table]

Fromtable_source

[Wheresearch_condition]

[GROUPBY Group_by_expression]

[Havingsearch_condition]

[by Order_expression [ASC | DESC]]

Example: Find out the payroll for an employee with 007 in the EMP list

Selectt.sal

From empt

WHERE t.id =007

the application in architecture

In the building structure diagram, the DQL represents the underground ring beam, which usually appears in the strip base.

It should be set in the 08 list 010403003 Circle Beam.