SQL基础教程（第2版）第6章 函数、谓词、CASE表达式：练习题

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SELECT SUM(CASE WHEN sale_price <= 1000 THEN 1 ELSE 0 END)               AS low_price,
       SUM(CASE WHEN sale_price BETWEEN 1001 AND 3000 THEN 1 ELSE 0 END) AS mid_price,
       SUM(CASE WHEN sale_price >= 3001 THEN 1 ELSE 0 END)               AS high_price
 FROM Product;