Head First SQL的精要

这是一本很好的SQL入门书。

很好的SQL练习题：https://leetcode.com/studyplan/top-sql-50/

第一章

SQL is case-insensitive. But it’s considered a good programming practice in SQL.

CREATE DATABASE gregs_list;

The semicolon is there to indicate that the command has ended.

TIMESTAMP is usually used to capture the current time. DATETIME is best used to store a future event.

DESC命令

To see how my_contacts table you created looks, you can use the DESC command to view it:

DESC my_contacts;

DESC is short for DESCRIBE.

INSERT语句

INSERT INTO your_table (column_name1, column_name2,...) VALUES ('value1', 'value2',...);

IMPORTANT: the values need to be in the same order as the column names.

Any value that goes into a VARCHAR, CHAR, DATE, or BLOB column has single quotes around it.

NULL相当于undefined。

You can’t compare one NULL to another. A value can be NULL, but it never equals NULL because NULL is an undefined value!

第四章

LIKE isn’t specific enough to target precise data.

… consider how much room on your hard drive it will take up when your database grows to an enormous size.

Cartesian join（亦称Cross join或Cartesian product）

A Cartesian join is a type of inner join. An inner join is basically just a Cartesian join where some results rows are removed by a condition in the query.

An outer joins returns all rows from one of the tables, along with matching information from another table.