介紹
此文為 SQL to Pandas 系列第二篇
可先閱讀
補充上篇 JOIN 內容
本篇將解構下面的 SQL 查詢句式, 使用 Pandas 進行實現
SQL 查詢句式
SELECT DISTINCT [欄位]
FROM [表] JOIN [bin] ON [連線條件]
WHERE [過濾條件]
GROUP BY [欄位]
HAVING [條件]
ORDER BY [欄位] DESC
LIMIT [個數] OFFSET [個數]
複製程式碼讀取評論資料
df_comments = pd.read_sql(sql="select * from comments", con=conn)
複製程式碼資料預覽
df_comments
複製程式碼| id | student_id | content | |
|---|---|---|---|
| 0 | 1 | 1 | 測試評論1 |
| 1 | 2 | 5 | 測試評論5 |
| 2 | 3 | 2 | 測試評論2 |
| 3 | 4 | 3 | 測試評論3 |
| 4 | 5 | 1 | 測試評論11 |
| 5 | 6 | 9 | 測試評論9 |
JOIN
(INNER) JOIN
SQL
SELECT
*
FROM
student
INNER JOIN comments ON student.id = comments.student_id;
複製程式碼Pandas
pd.merge(df, df_comments, left_on='id', right_on='student_id')
複製程式碼LEFT (OUTER) JOIN
SQL
SELECT
*
FROM
student
LEFT JOIN comments ON student.id = comments.student_id;
複製程式碼Pandas
pd.merge(df, df_comments, left_on='id', right_on='student_id', how='left')
複製程式碼RIGHT (OUTER) JOIN
SQL
SELECT
*
FROM
student
RIGHT JOIN comments ON student.id = comments.student_id;
複製程式碼Pandas
pd.merge(df, df_comments, left_on='id', right_on='student_id', how='right')
複製程式碼UNION
SQL
SELECT * FROM student where city ='北京'
UNION
SELECT * FROM student where sex ='男';
複製程式碼Pandas
pd.concat([df[df.city == '北京'], df[df.sex == '男']]).drop_duplicates().reset_index()
複製程式碼UNION ALL
SQL
SELECT * FROM student where city ='北京'
UNION ALL
SELECT * FROM student where sex ='男';
複製程式碼Pandas
pd.concat([df[df.city == '北京'], df[df.sex == '男']]).reset_index()
複製程式碼本篇內容
本篇將解構下面的 SQL 查詢句式, 使用 Pandas 進行實現
SQL 建立句式
CREATE TABLE [表名] (
[列名] [型別],
[列名] [型別],
....
);
複製程式碼SQL 插入句式
INSERT INTO [表名] VALUES ([值], [值], ...);
INSERT INTO [表名] ([列名],[列名] ...) VALUES ([值], [值], ...);
複製程式碼SQL 更新句式
UPDATE [表名]
SET [列名] = [值], [列名] = [值]
WHERE [過濾條件];
複製程式碼SQL 刪除句式
DELETE FROM [表名] WHERE [過濾條件];
複製程式碼CREATE
SQL
CREATE TABLE student (
id INT ( 11 ) NOT NULL AUTO_INCREMENT,
name VARCHAR ( 10 ) COLLATE utf8mb4_general_ci DEFAULT NULL,
age date DEFAULT NULL,
sex VARCHAR ( 10 ) COLLATE utf8mb4_general_ci DEFAULT NULL,
city VARCHAR ( 255 ) CHARACTER
SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL,
money DOUBLE ( 255, 2 ) DEFAULT NULL,
);
複製程式碼Pandas
pd.DataFrame(columns=['id', 'name', 'sex', 'city', 'money'])
複製程式碼INSERT
SQL
INSERT INTO student (id, name, age, sex, city, money )
VALUES
(1, '張三', '2017-12-20', '女', '天津', 20.00 );
複製程式碼Pandas
# 第一種
df.loc[-1] = [1, '張三', '女', '天津', 20.00]
df.index = df.index + 1
df = df.sort_index()
# 第二種
temp_pd = pd.DataFrame({'id': [1], 'name': ['張三'], 'sex': ['女'], 'city': ['天津'], 'money': [20.00]})
df = pd.concat([df,temp_pd], ignore_index=True)
df.reset_index()
# 第三種
temp_pd = pd.DataFrame([[1,'張三1', '女', '天津', 20.00]], columns=df.columns)
df = pd.concat([df, temp_pd])
df.reset_index()
複製程式碼UPDATE
SQL
UPDATE student SET money = 300 WHERE id = 1;
複製程式碼Pandas
df.loc[df.id == 1, 'money'] = 300
複製程式碼DELETE
SQL
-- 測試時會因外來鍵報錯，此處忽略，僅討論句法
DELETE FROM student WHERE id = 1;
複製程式碼Pandas
df = df.loc[df.id != 1]
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