🔄Update: MySQL

MySQL/10. 检索.md

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+# 检索
+
+1. 检索列
+
+```sql
+SELECT cust_id
+FROM Customers
+```
+
+2. 检索列去重
+
+```sql
+SELECT DISTINCT prod_id
+FROM OrderItems
+```
+
+3. 检索列排序
+
+```sql
+SELECT cust_name
+FROM Customers
+ORDER BY cust_name DESC
+```
+
+4. 检索列双重排序
+
+```sql
+SELECT cust_id, order_num
+FROM Orders
+ORDER BY cust_id, order_date DESC
+```
+
+```sql
+SELECT quantity, item_price
+FROM OrderItems
+ORDER BY quantity DESC, item_price DESC
+```
+
+5. 等值查找
+
+```sql
+SELECT prod_id, prod_name
+FROM Products
+WHERE prod_price = 9.49
+```
+
+6. 范围查找
+
+```sql
+SELECT prod_id, prod_name
+FROM Products
+WHERE prod_price >= 9
+```
+
+7. 范围查找排序
+
+```sql
+SELECT prod_name, prod_price
+FROM Products
+WHERE prod_price BETWEEN 3 AND 6
+ORDER BY prod_price
+```
+
+8. 分组筛选
+
+```sql
+SELECT order_num
+FROM OrderItems
+GROUP BY order_item
+HAVING SUM(quantity) >= 100
+```
+
+9. 区域匹配
+
+```sql
+SELECT order_num, prod_id, quantity
+FROM OrderItems
+WHERE prod_id IN ('BR01', 'BR02', 'BR03') AND quantity >= 100
+```
+
+10. 模糊匹配
+
+```sql
+SELECT prod_name, prod_desc
+FROM Products
+WHERE prod_desc LIKE '%toy%'
+```
+
+11. 别名
+
+```sql
+SELECT vend_id, vend_name AS vname, vend_address AS vaddress, vend_city AS vcity
+FROM Vendors
+ORDER BY vname
+```
+
+12. 列计算
+
+```sql
+SELECT prod_id, prod_price, prod_price * 0.9 AS sale_price
+FROM Products
+```
+
+13. 函数
+
+```sql
+SELECT cust_id, cust_name, UPPER(CONCAT(SUBSTRING(cust_contact, 1, 2), SUBSTRING(cust_city, 1, 3))) AS user_login
+FROM Customers
+```
+
+```sql
+SELECT order_num, COUNT(*) AS items
+FROM OrderItems
+GROUP BY order_num
+HAVING items >= 3
+ORDER BY items, order_num
+```
+
+
+14. 子查询
+
+```sql
+SELECT cust_id
+FROM Orders
+WHERE order_num IN (SELECT DISTINCT order_num
+    FROM OrderItems
+    where item_price >= 10)
+```

MySQL/11. 表连接.md

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+# 表连接
+
+![SQL JOINS](https://oss.javaguide.cn/github/javaguide/csdn/d1794312b448516831369f869814ab39.png)
+