What's SQL?

SQL (Structured Query Language) It is a standard programming language for managing the relationship database. Whether it's a simple blog system or a complex enterprise-level ERP, SQL These are the cornerstones of data interaction. It allows developers to perform tasks such as searching data, updating records, deleting records and creating and modifying database structures.

Why do you need SQL key word quick check?

Although the core syntax of SQL is relatively stable, different database systems (e.g. MySQL, PostgreSQL, Oracle, SQL) Some variation in the details of the achievement is achieved by Server. In addition, many high-level functions and specific sub-paragraphs (e.g., HAVING , UNION or window functions) are not always used frequently in day-to-day development.

Quick memory awakening: Help developers forget specific grammar (e.g. UPDATE ) Quickly find reference.
Improved efficiency of preparation: Include examples that are commonly used, which are copied directly and modified by the actual name, to reduce debugging time.
Understanding core concepts: Distinction WHERE and HAVING ♪ Understand differently ♪ JOIN The application scene.

SQL Syntax Core Classification

1. Data query language (DQL)

Here. SELECT It's at the core, it's adopted. WHERE The #Feb14 blog is a good example of the #Feb14. GROUP BY Grouping, ORDER BY Sorting. This is the most common part of development.

2. Data Operating Language (DML)

Organisation INSERT , UPDATE , DELETE , and so on, as a list of the data in the table. Be careful with the operation. WHERE Sub-paragraph, to prevent the deletion of the entire table.

3. Data definition language (DDL)

Involving CREATE , ALTER , DROP , which defines or changes the logical structure of the database (tables, indexes, views, etc.).

4. Aggregation functions

Like COUNT , SUM , AVG , MAX/MIN This is often used for statistical analysis of data, which, in conjunction with cluster operations, produces robust operational statements.

Specific issues addressed

The quick check tool aims to address the following practical development pain points:

Multi-table connectivity disorder: Quick Distinction LEFT JOIN , RIGHT JOIN and INNER JOIN results set differences.
Page break search fit: Provide generic LIMIT and OFFSET Syntax:
Complex filter conditions: Presentation IN , BETWEEN , LIKE . The correct use of the condition operator.