After learning the database installation, the most important thing is to learn SQL statements.
SQL is the core of operating the database, and it is also the sentence at the beginning of this chapter: For PHP programmers, MySQL is to convert business into a table structure. Do a good job of adding, deleting, modifying, and checking in the business.
Structured Query Language (SQL), referred to as SQL, is a special-purpose programming language. It is a database query and programming language used to access data and query, update and manage relational databases. System; also the extension of the database script file.
SQL is the most important relational database operating language, and its influence has exceeded the database field and has been valued and adopted in other fields, such as data retrieval in the field of artificial intelligence.
SQL is a database application language for the relational model, developed by IBM in the 1970s for its relational database System R.
SQL is an American standard for database language adopted by the American National Standards Institute (ANSI) in October 1986. Subsequently, the International Organization for Standardization (ISO) promulgated the official international standard for SQL. In April 1989, ISO proposed the SQL89 standard with integrity characteristics, and in November 1992, the SQL92 standard was announced.
Although each database system is slightly different, they basically follow the SQL 92 standard. Or made some simple extensions and changes on SQL 92.
After learning the SQL syntax of MySQL, other SQL syntax is indispensable for learning.
SQL statements can be divided into 3 categories according to their functional scope:
- Data Definition Language (DDL, Data Definition Language) statement: data definition statement , used to define different data segments, databases, tables, columns, indexes, etc. Commonly used statement keywords include create, drop, alter, etc.
- Data Manipulation Language(DML, Data Manipulation Language) statement: Data manipulation statement, used to add, delete, update and query database records, and check the integrity of the data. Commonly used statement keywords mainly include insert, delete, update, select, etc.
- Data Control Language(DCL, Data Control Language) statement: Data control statement, a statement used to control the direct permission and access levels of different data segments. These statements define the database, tables, fields, user access rights and security levels. The main statement keywords include grant, revoke, etc.
