SQL INSERT 但如果存在则增加 ID 而无需执行单独的 SELECT 查询

Question

我有一个表，主键在两列上：

ID

（用户 ID）和

SQ

（序列，从 1 开始，每个

ID

递增 +1）。一个用户不应该有相同序列号的多个实例。这是表格的样子：

ID      SQ    Code
------  --    ----
123456  1     123
654321  1     369
123456  2     234

我正在尝试在

Code

列中插入一个值，但在我这样做之前，我需要检查特定用户是否已经拥有该代码，如果是，请接收序列号。

目前，我运行：

# CodeExists is 1 if user has code already. 0 otherwise
# Max_SQ gives the maximum SQ that exists for this user
cursor.execute("SELECT MAX(CASE WHEN Code = ? THEN 1 ELSE 0 END) AS 'CodeExists', MAX(SQ) AS 'Max_SQ' FROM TABLENAME WHERE ID = ? GROUP BY ID", Code, User_PID)
data = cursor.fetchone()
if data is None: # This user does not have any codes, SQ starts at 1
    SQ = 1
else:
    CodeExists, SQ = data # Unpack query values
    if int(CodeExists) == 1: # User already has the code we are trying to insert, skip
        continue
    else:
        SQ = int(SQ) + 1 # Increment SQ
cursor.execute("INSERT INTO TABLENAME (ID,SQ,Code) VALUES(?,?,?)", User_PID, SQ, Code)
cursor.commit()

例子：

• 尝试为用户 =123456 插入代码 =123，不应插入。该用户已有代码 123。
• 尝试为用户 =654321 插入代码 =123，应该使用 SQ=2 插入
• 尝试为用户=999999 插入代码=123，应该插入 SQ=1

给定代码 # 和用户 ID，有没有办法将其组合成单个 INSERT 查询？

Answer 1

使用 CTE 存储新行的

ID

和

Code

。
然后将 CTE

LEFT

连接到表并聚合以获得该

SQ

的最大

ID

并将其增加 1.
在

HAVING

子句中设置条件，如果表中已经有一行代码与 CTE 中的代码相同，则查询不应返回要插入的任何行。

这是查询：

WITH cte AS (SELECT * FROM (VALUES (123456, 123))t (ID, Code))
INSERT INTO tablename (ID, SQ, Code)
SELECT c.ID,
       COALESCE(MAX(t.SQ), 0) + 1,
       c.Code
FROM cte c LEFT JOIN tablename t
ON t.ID = c.ID 
GROUP BY c.ID, c.Code
HAVING MAX(CASE WHEN c.Code = t.Code THEN 1 END) IS NULL;

查看演示。

Answer 2

在 MysQL 中你可以这样做

CREATE TABLE TABLENAME
    (`ID` int, `SQ` int, `Code` int)
;
    
INSERT INTO TABLENAME
    (`ID`, `SQ`, `Code`)
VALUES
    (123456, 1, 123),
    (654321, 1, 369),
    (123456, 2, 234)
;

INSERT INTO TABLENAME (ID,SQ,Code) 
SELECT 1223344,( SELECT COALESCE(MAX(SQ),0) +1 FROM TABLENAME  WHERE ID =  1223344) ,666 
WHERE  NOT EXISTS ( SELECT 1 FROM TABLENAME  WHERE ID =  1223344 AND Code = 666)

Records: 1  Duplicates: 0  Warnings: 0

INSERT INTO TABLENAME (ID,SQ,Code) 
SELECT 123456,( SELECT COALESCE(MAX(SQ),0) +1 FROM TABLENAME  WHERE ID =  123456) ,666 
WHERE  NOT EXISTS( SELECT 1 FROM TABLENAME  WHERE ID =  123456 AND Code = 666)

Records: 1  Duplicates: 0  Warnings: 0

INSERT INTO TABLENAME (ID,SQ,Code) 
SELECT 1223344,( SELECT COALESCE(MAX(SQ),0) +1 FROM TABLENAME  WHERE ID =  1223344) ,666 
WHERE  NOT EXISTS( SELECT 1 FROM TABLENAME  WHERE ID =  1223344 AND Code = 666)

Records: 0  Duplicates: 0  Warnings: 0

SELECT * FROM TABLENAME

ID	平方	代码
123456	1	123
654321	1	369
123456	2	234
1223344	1	666
123456	3	666

小提琴