10 丨 What are the commonly used SQL standards, and how is the connection used in SQL92?
11 丨 How does SQL99 use connection, what is the difference with SQL92?
12 丨 What is the role of view in SQL and how does it work?
What is the underlying principle of the view? What are the operation steps of executing a query statement?
Author's reply: A view is actually a collection of SELECT statements, which will be compiled in advance when executed and can be used repeatedly. The order of execution at the bottom is the same as the SELECT statement:
1. FROM clause assembly data
2. WHERE clause for conditional filtering
3. GROUP BY grouping
4. Calculation using aggregate functions;
5. HAVING filtering grouping;
6. Calculating all Expression;
7, SELECT field;
8, ORDER BY sort
9, LIMIT filter
13 丨 What is a stored procedure and how is it used in actual projects?
