tailieunhanh - Hướng dẫn sử dụng MySQL part 4

Các Structured Query Language (SQL) là ngôn ngữ được sử dụng để đọc và ghi vào cơ sở dữ liệu MySQL. Sử dụng SQL, bạn có thể tìm kiếm dữ liệu, nhập dữ liệu mới, sửa đổi dữ liệu, hoặc xóa dữ liệu. SQL chỉ đơn giản là công cụ cơ bản nhất, bạn sẽ cần cho tương tác của bạn với MySQL. Ngay cả khi bạn đang sử dụng một số ứng dụng hoặc giao diện người dùng đồ họa để truy cập vào cơ sở dữ liệu, một nơi nào đó dưới sự bao gồm các ứng dụng. | _DRAFT 8 20 01 4 SQL According to MySQL The Structured Query Language SQL is the language used to read and write to MySQL databases. Using SQL you can search for data enter new data modify data or delete data. SQL is simply the most fundamental tool you will need for your interactions with MySQL. Even if you are using some application or graphical user interface to access the database somewhere under the covers that application is generating SQL. SQL is a sort of natural language. In other words an SQL statement should read at least on the surface like a sentence of English text. This approach has both benefits and drawbacks but the end result is a language very unlike traditional programming languages such as C Java or Perl. SQL Basics SQL is structured in the sense that it follows a very specific set of rules. A computer program can easily parse a formulated SQL query. In fact the O Reilly book lex yacc by John Levine Tony Mason and Doug Brown implements a SQL grammar to demonstrate the process of writing a program to interpret language A query is a fully-specified command sent to the database server which then performs the requested action. Below is an example of an SQL query SELECT name FROM people WHERE name LIKE Stac As you can see this statement reads almost like a form of broken English Select names from a list of people where the names are like Stac. SQL uses very few of Pronounced either sequel or ess-que-ell. Certain people get very religious about the pronunciation of SQL. Ignore them. It is important to note however that the SQL in MySQL is properly pronounced ess-que-ell. Copyright 2001 O Reilly Associates Inc. 54 DRAFT 8 20 01 the formatting and special characters that are typically associated with computer languages. Consider for example A in Perl versus SELECT value FROM table in SQL. The SQL Story IBM invented SQL in the 1970s shortly after Dr. E. F. Codd first invented the concept of a relational database. From the beginning SQL