出了什么问题？

我认为您的问题是SELECT ....应该放在括号中。

修复(假设我在正确的位置添加了括号，如果没有，请参见下面的演示)

query1=conn.execute(text(("INSERT INTO temporary (train%s) VALUES ((SELECT (train.%s-ideal.%s)*(train.%s-ideal.%s) FROM train INNER JOIN ideal ON train.x=ideal.x))")%(train_no,col_train,col_ideal,col_train,col_ideal)))

以下是工作SQL的演示(尽管表可能不同)：

DROP TABLE IF EXISTS train;
DROP TABLE IF EXISTS ideal;
DROP TABLE IF EXISTS temporary;
CREATE TABLE IF NOT EXISTS train (x INTEGER PRIMARY KEY, train_no INTEGER,col_train TEXT);
CREATE TABLE IF NOT EXISTS ideal (x INTEGER PRIMARY KEY, col_ideal INTEGER, col_train INTEGER);
CREATE TABLE IF NOT EXISTS temporary (train_no INTEGER);
INSERT INTO temporary (train_no) VALUES (
    ( /*<<<<<<<<<< ADDED */
        SELECT (train.col_train-ideal.col_ideal)*(train.col_train-ideal.col_ideal) 
        FROM train INNER JOIN ideal ON train.x=ideal.x
    ) /*<<<<<<<<<< ADDED */
);

当签立时：

INSERT INTO temporary (train_no) VALUES (
    ( /* ADDED */
        SELECT (train.col_train-ideal.col_ideal)*(train.col_train-ideal.col_ideal) 
        FROM train INNER JOIN ideal ON train.x=ideal.x
    ) /* ADDED */
)
> Affected rows: 1
> Time: 0.084s

与(不带括号)相反：-

INSERT INTO temporary (train_no) VALUES (
    /*(*/ /* ADDED */
        SELECT (train.col_train-ideal.col_ideal)*(train.col_train-ideal.col_ideal) 
        FROM train INNER JOIN ideal ON train.x=ideal.x
    /*)*/ /* ADDED */
)
> near "SELECT": syntax error
> Time: 0s