SELECT expression1, expression2, ... expression_n FROM tables [WHERE conditions]
UNION [ALL | DISTINCT]
SELECT expression1, expression2, ... expression_n FROM tables [WHERE conditions];
Mysql排序:
使用 MySQL 的 ORDER BY 子句來設定想按哪個字段哪種方式來進行排序,再返回搜索結果。
SELECT field1, field2,...fieldN table_name1, table_name2...
ORDER BY field1, [field2...] [ASC [DESC]]
GROUP BY 語句根據一個或多個列對結果集進行分組。
在分組的列上我們可以使用 COUNT, SUM, AVG,等函數
SELECT name, COUNT(*) FROM employee_tbl GROUP BY name;
INNER JOIN(內連接,或等值連接):獲取兩個表中字段匹配關係的記錄。
LEFT JOIN(左連接):獲取左表所有記錄,即使右表沒有對應匹配的記錄。
RIGHT JOIN(右連接): 與 LEFT JOIN 相反,用於獲取右表所有記錄,即使左表沒有對應匹配的記錄。
SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a INNER JOIN tcount_tbl b ON a.runoob_author = b.runoob_author;
SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a, tcount_tbl b WHERE a.runoob_author = b.runoob_author;
SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a LEFT JOIN tcount_tbl b ON a.runoob_author = b.runoob_author;
SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a RIGHT JOIN tcount_tbl b ON a.runoob_author = b.runoob_author;