Question

我试图删除一个简单表中除了id最高的副本之外具有重复值的所有行。

表：

CREATE TABLE IF NOT EXISTS [Expression] (
                      [ID] INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
                      [Value] VARCHAR(2048) NOT NULL
                      )

尝试查询：

DELETE Expression 
WHERE EXISTS (
    SELECT 1 
    FROM Expression Exp2 
    WHERE Expression.Value=Exp2.Value 
        AND Expression.Id < Exp2.Id)

失败，出现“SQL逻辑错误或数据库丢失”表达式“：语法错误”

DELETE Exp1 
FROM Expression Exp1 
  INNER JOIN Expression Exp2 
    ON Exp1.Value=Exp2.Value AND Exp1.Id < Exp2.Id

失败，出现“SQL逻辑错误或数据库丢失”Exp1“：语法错误”

我需要使用哪种语法？

Answer 1

不要忘记 FROM 。

DELETE command

DELETE FROM Expression 
WHERE EXISTS (
    SELECT 1 
    FROM Expression Exp2 
    WHERE Expression.Value=Exp2.Value 
    AND Expression.Id < Exp2.Id
);

Answer 2

您可以通过多种方式实现这一目标：

1）使用CTE：

    WITH CTE AS (
    SELECT ID, VALUE, ROW_NUMBER() OVER(ORDER BY Value) as RowNum
    FROM Expression
     )
  DELETE 
   FROM CTE 
    WHERE ROWNum >1

2）使用临时表：相同的概念

Answer 3

从联系人t1的内部联接中删除t1 t1.id

SQLITE - 使用自联接删除行？

3 个答案: