Mysql-Basic Rules and Specifications

Classification of SQL

• DDL (Data Definition Language) includes CREATE, DROP, ALTER, RENAME, TRUNCATE and other keywords used to create, delete, and modify the structure of databases and data tables.
• DML (Data Manipulation Language) includes INSERT, DELETE, UPDATE, SELECT and other keywords used to add, delete, update, query (sometimes independent as DQL) database records.
• DCL (Data Contril Language) includes GRANT, REVOKE, COMMIT, ROLLBACK, SAVEPOINT and other keywords used to define security levels and access rights.

Rules and Specifications of SQL

basic rules

• SQL can be written in one line or multiple lines. For readability, it is recommended to write clauses in separate lines and introduce necessary indentation.
• Every SQL statement ends with an English semicolon ';' or \g, \G.
• Keywords cannot be abbreviated and cannot be divided into lines
• Single quotes can be used for string and date data, and double quotes should be used for other column names. It is not recommended to omit as.

case specification

• Database name, table name, table alias, variable name, field alias are all lowercase
• SQL keywords, function names, and bind variables are capitalized

Annotation Specification

• MySQL-specific single-line comment method: #Comment text
• Single-line comment method: -- comment text -- remember two -- there must be a space after
• Multi-line comment method: / comment text /