SQL Introduction "SQL action type"

After learning the database installation, the most important thing is to learn SQL statements.

SQL is the core of the operational database and the beginning of this chapter: MySQL for PHP programmers is to transform the business into a table structure. Do business in the increase, delete, change, check.

The Structured Query Language (structured query Language) is a special purpose programming language, a database query and programming language for accessing data and querying, updating and managing relational database systems, as well as the extension of database script files.

SQL is the most important relational database operation language, and its influence has gone beyond the domain of database, and has been paid attention to and adopted in other fields, such as data retrieval in artificial intelligence field.

SQL is the database application language of the relational model, developed by IBM in the 1970s for its relational database System R.

SQL is the American Standard of database language adopted by the United States National Standards Agency (ANSI) in October 1986, and then the International Organization for Standardization (ISO) promulgated the formal international standard for SQL. In April 1989, ISO presented the SQL89 standard with integrity features, and the SQL92 standard was released in November 1992.

Although each database system is slightly different, they basically follow the SQL 92 standard. Or, some simple extensions and changes are made on SQL 92.

Learn the SQL syntax of MySQL, the other SQL syntax learning is a change.

SQL statements can be divided into 3 categories depending on their functional scope:

1. Data Definition Language (DDL, data defintion Language) statement: A data definition statement that defines different data segments, databases, tables, columns, indexes, and so on. Common statement keywords include create, drop, alter, and so on.
2. Data Manipulation Language (DML, data manipulation Language) statement: Data manipulation statements for adding, deleting, updating, and querying database records, and for checking the integrity of data. Common statement keywords include insert, delete, update, select, and so on.
3. Data Control Language (DCL, Data Control Language) statement: A data-controlled statement that controls the level of permission and access to different data segments directly. These statements define the database, table, field, user's access rights, and security level. The main statement keywords include GRANT, revoke, and so on.

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SQL Introduction "SQL action type"