The Statement Structure of SQL (PartⅡ)
Introduction of SQL SQL, short for Structured Query Language, which is a programming language to access and manipulate databases, meanwhile, it’s as one of ANSI standard. SQL is not only used to access & query data, but also to update and manage the relational database systems. Obviously, the latter function shows its strong performances of Structured Query Language and it’s what critical to administrators. If you want to know more about Structured Query Language, please refer to my last post at SQL Structured Query Language. SQL Sentence Structure Although there are so many computer programming languages, it seems that not only common points but obvious differences will exist in them. Thus it’s critical to know the statement structure if we want to know about SQL. In this article, we’ll get to know the statement structure of SQL.Let us divide it into six sections to discuss: I Data Query Language DQL: shorted for Data Query Language. It also is called "data retrieval statement" which is used to get the data from the table, and to determine the way that data are given in the application. SELECT statement is the most popular verbs in DQL (also for SQL), along with common reserved words like WHERE, ORDER BY, GROUP BY, and so on. In general, these DQL reserved words often comes with conjunction of other types of SQL statements. II Data Manipulation Language DML: stands for Data Manipulation Language. It also is called action query language. These types of statements are verbs like INSERT, UPDATE, and DELETE. They are used to add, modify, and delete rows in the table. For example, insert into table 1(field1,field2) values(value1,value2),it’s a typical insert statement to add a record. III Transaction Processing Language Transaction Processing Language (TPL): Its statement can ensure all the rows in tables which are referred in DML statements timely updated. TPL statements include BEGIN TRANSACTION, COMMIT, and ROLLBACK. IV Data Control Language Data Control Language (DCL): It GRANT or REVOKE statement obtained by permission of individual users and user groups to determine access to database objects. Some RDBMS can be used to control access to single row in tables by GRANT or REVOKE. V Data Definition Language Data Definition Language (DDL): It is also part of the action query. DDL include CREATE and DROP statements. DDL are used to create a new table or delete tables (CREAT TABLE or DROP TABLE) in the database; they are able to add indexes to table. DDL remains a lot related reserved words who obtained the data in the database directory. VI Pointer Control Language Pointer Control Language (CCL): It used for single rows operation in a table or tables which include DECLARE CURSOR, FETCH INTO and UPDATE WHERE CURRENT statements.
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