OracleThe database is a powerful relational database management system that supports data retrieval and operation using SQL query language. The following are some commonly used Oraclequery statement examples:
1. Select data (SELECT):
- Query all columns:
SELECT * FROM 表名; - Query specific columns:
SELECT 列名1, 列名2 FROM 表名; - Query and add conditions:
SELECT * FROM 表名 WHERE 条件; - Use wildcards:
SELECT 列名 FROM 表名 WHERE 列名 LIKE 模式; - Sort query results:
SELECT * FROM 表名 ORDER BY 列名 ASC/DESC; - Grouped aggregation query:
SELECT 列名, 聚合函数(列名) FROM 表名 GROUP BY 列名;
2. Insert data (INSERT):
- Insert a row of data:
INSERT INTO 表名 (列名1, 列名2) VALUES (值1, 值2);
3. Update data (UPDATE):
- update data:
UPDATE 表名 SET 列名 = 新值 WHERE 条件;
4. Delete data (DELETE):
- delete data:
DELETE FROM 表名 WHERE 条件;
5. Connection table (JOIN):
- Inner join:
SELECT * FROM 表名1 INNER JOIN 表名2 ON 表名1.列名 = 表名2.列名; - Left join:
SELECT * FROM 表名1 LEFT JOIN 表名2 ON 表名1.列名 = 表名2.列名;
6. Subquery:
- Scalar subquery:
SELECT 列名 FROM 表名 WHERE 列名 = (SELECT 列名 FROM 表名 WHERE 条件); - List query:
SELECT 列名1, 列名2 FROM 表名 WHERE 列名 IN (SELECT 列名 FROM 表名 WHERE 条件);
7. Aggregation function:
- Sum:
SELECT SUM(列名) FROM 表名; - average value:
SELECT AVG(列名) FROM 表名; - Maximum value:
SELECT MAX(列名) FROM 表名; - Minimum value:
SELECT MIN(列名) FROM 表名; - count:
SELECT COUNT(列名) FROM 表名;
8. Conditional judgment:
- CASE expression: used for conditional judgment and value mapping in query results.
SELECT 列名, CASE WHEN 条件1 THEN 值1 WHEN 条件2 THEN 值2 ELSE 默认值 END AS 新列名 FROM 表名;
The above are just some common query examples. Oracle SQLThe syntax is very rich, and more complex queries and operations can be performed according to specific situations. In actual use, appropriate query statements need to be written based on the table structure, data content and specific needs.