sql - 动态 SQL : Create insert queries for tables having relations

Question

我有 2 张 table ，foo和 bar . bar持有 foo 的外键， 如 :

foo

id | some_data
-: | :--------
 1 | a
 2 | b
 3 | c

酒吧

id | id_foo | more_data
-: | -----: | :--------
 1 |      1 | d
 2 |      1 | e
 3 |      2 | f
 4 |      3 | g
 5 |      3 | h
 6 |      3 | i

我想动态创建查询以插入其他地方 foo和 bar .

为表foo ，这很容易完成:

SELECT CONCAT('INSERT INTO new_foo (some_data) VALUES (''', f.some_data, ''');') AS 'sql'
FROM foo f;

我得到了这个预期的结果:

INSERT INTO new_foo (some_data) VALUES ('a');
INSERT INTO new_foo (some_data) VALUES ('b');
INSERT INTO new_foo (some_data) VALUES ('c');

但是，我一直在为包含外键的表生成插入查询。

我想使用 2 UNION s，一个获取最后插入的 id，第二个使用这个 id 生成对 bar 的查询:

SELECT sql
FROM
(
    SELECT f.id AS 'id', CONCAT('INSERT INTO new_foo (some_data) VALUES (''', f.some_data, ''');') AS 'sql'
    FROM foo f
    UNION
    SELECT f.id AS 'id', 'SET @last_id = SELECT LAST_INSERT_ID();' AS 'sql' -- Target will be MySQL
    FROM foo f
    UNION
    SELECT b.id_foo AS 'id', CONCAT('INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, ''', b.more_data, ''');') AS 'sql'
    FROM bar b
) s
ORDER BY s.id;

这给了我作为输出:

INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'd');
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'e');
INSERT INTO new_foo (some_data) VALUES ('a');
SET @last_id = SELECT LAST_INSERT_ID();
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'f');
INSERT INTO new_foo (some_data) VALUES ('b');
SET @last_id = SELECT LAST_INSERT_ID();
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'g');
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'h');
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'i');
INSERT INTO new_foo (some_data) VALUES ('c');
SET @last_id = SELECT LAST_INSERT_ID();

查询的顺序是错误的。它首先生成对 bar 的查询，然后 foo ，然后 LAST_INSERT_ID() .

它应该是 :

INSERT INTO new_foo (some_data) VALUES ('a');
SET @last_id = SELECT LAST_INSERT_ID();
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'd');
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'e');
INSERT INTO new_foo (some_data) VALUES ('b');
SET @last_id = SELECT LAST_INSERT_ID();
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'f');
INSERT INTO new_foo (some_data) VALUES ('c');
SET @last_id = SELECT LAST_INSERT_ID();
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'g');
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'h');
INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, 'i');

如何确保遵守正确的顺序？我可以在 UNION 中处理每个查询的位置，但我不确定是否会保留条目的顺序。

这是一个 fiddle和玩

Answer 1

您有具有相同 ID 的三行，并且未指定顺序。您可以添加一个新列来指定顺序:

SELECT sql
FROM
(
    SELECT f.id AS 'id', -1 AS seq, CONCAT('INSERT INTO new_foo (some_data) VALUES (''', f.some_data, ''');') AS 'sql'
    FROM foo f
    UNION
    SELECT f.id AS 'id', 0 AS seq, 'SET @last_id = SELECT LAST_INSERT_ID();' AS 'sql' -- Target will be MySQL
    FROM foo f
    UNION
    SELECT b.id_foo AS 'id', b.id AS seq, CONCAT('INSERT INTO new_bar (id_foo, more_data) VALUES (@last_id, ''', b.more_data, ''');') AS 'sql'
    FROM bar b
) s
ORDER BY s.id, s.seq;