Learning MySQL from Scratch: Mastering Data Extraction with Query Statements
This article introduces the basics of MySQL. First, it explains that MySQL is an open-source relational database used for storing structured data (such as users, orders, etc.). Before use, it needs to be installed and run, and then connected through graphical tools or command lines. Data is stored in the form of "tables", which are composed of "fields" (e.g., id, name). For example, a student table includes fields like student ID and name. Core query operations include: basic queries (`SELECT * FROM table_name` to retrieve all columns, `SELECT column_name` to specify columns, `AS` to set aliases); conditional queries (`WHERE` combined with comparison operators, logical operators, and `LIKE` for fuzzy matching to filter data); sorting (`ORDER BY`, default ascending `ASC`, descending with `DESC`); limiting results (`LIMIT` to control the number of returned rows); and deduplication (`DISTINCT` to exclude duplicates). It also provides comprehensive examples and practice suggestions, emphasizing familiarizing oneself with query logic through table creation testing and combined conditions. The core of MySQL queries: clarify requirements → select table → specify columns → add conditions → sort/limit. With more practice, one can master query operations proficiently.
Read MoreSQL Introduction: How to Create and Manipulate Data Tables in MySQL?
A data table is a "table" for storing structured data in a database, composed of columns (defining data types) and rows (recording specific information). For example, a "student table" contains columns such as student ID and name, with each row corresponding to a student's information. To create a table, use the `CREATE TABLE` statement, which requires defining the table name, column names, data types, and constraints (e.g., primary key `PRIMARY KEY`, non-null `NOT NULL`, default value `DEFAULT`). Common data types include integer `INT`, string `VARCHAR(length)`, and date `DATE`. Constraints like auto-increment primary key `AUTO_INCREMENT` ensure uniqueness. To view the table structure, use `DESCRIBE` or `SHOW COLUMNS`, which display column names, types, and whether null values are allowed. Operations include: - Insertion: `INSERT INTO` (specify column names to avoid order errors), - Query: `SELECT` (`*` for all columns, `WHERE` for conditional filtering), - Update: `UPDATE` (must include `WHERE` to avoid full-table modification), - Deletion: `DELETE` (similarly requires `WHERE`, otherwise the entire table is cleared). Notes: Strings use single quotes; `UPDATE`/`DELETE` must include `WHERE`; primary keys are unique and non-null.
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