這裡主要是整理 SQL 一些進階的語法，方便自己不記得的時候可以快速查詢。

Nested SELECT

/* general syntax */
SELECT column1, column2 FROM table1 WHERE column1 OPERATOR (SELECT column1 FROM table1 WHERE condition);

/* example 1 */
SELECT column1, column2 FROM table1 WHERE column1 < (SELECT AVG(column1) FROM table1);

/* example 2 */
SELECT column1, (SELECT MAX(column2) FROM table1) AS "Maximum" FROM table1;
 

Multiple Table

/* cross join */
SELECT column1, column2 FROM table1, table2;

/* inner join */
SELECT column1, column2 FROM table1, table2 WHERE table1.column3 = table2.column3;