如果该 id 不存在该行，则 SQL 为从另一个表返回的每个 id 插入多行

Question

I need to insert multiple rows into a table for every returned id from another table.

For example table1

id | thing1 |
---+--------|
1  |  true
2  |  false
3  |  true
4  |  false
5  |  true

Example table2

id |  table1_id  |     column3    |    column4   |
---+-------------|----------------|--------------|
1  |     1       |     'fizz'     |    'fizz'
2  |     1       |     'buzz'     |    'buzz'
3  |     1       | 'hello world'  | 'hello world'
4  |     2       |     'fizz'     |    'fizz'
5  |     2       |     'buzz'     |    'buzz'
6  |     2       | 'hello world'  | 'hello world'

I need to get every id from the above table1 where thing1 is true and insert multiple rows into table2 with the corresponding id as well as 2 other strings.

SELECT id FROM table1 WHERE thing1 = true

would return id 1, 3 and 5.

I would like to insert multiple rows adding the id from table1 as well as 2 other strings into table2.

INSERT into table2 (table1_id, column3, column4)
VALUES 
    (*id*, 'fizz', 'fizz')
    (*id*, 'buzz', 'buzz')
    (*id*, 'hello world', 'hello world')

I know how to get the ids and to manually insert but how can I do both with one statement?

Answer 1

I would suggest an INSERT... SELECT like so:

INSERT into table2 (table1_id, column3, column4)
SELECT t1.id, s.str, s.str
FROM table1 AS t1
CROSS JOIN (SELECT "fizz" AS str UNION SELECT "buzz" UNION SELECT "hello world") AS s
LEFT JOIN table2 AS t2 ON t1.id = t2.table1_id AND s.str = t2.column3
WHERE t1.thing1 = true
    AND t2.id IS NULL -- Only insert when they are not already present
;

However, this will not guarantee the strings are inserted in the order you've shown.

I have not had much call to use CROSS JOINs, so I am not sure how well they play with LEFT JOINs, so if the above does not work out quite right, here are some alternatives below:

INSERT into table2 (table1_id, column3, column4)
SELECT t1.id, s.str, s.str
FROM table1 AS t1
CROSS JOIN (SELECT "fizz" AS str UNION SELECT "buzz" UNION SELECT "hello world") AS s
WHERE t1.thing1 = true
    AND (t2.id, s.str) NOT IN (SELECT table1_id, column3 FROM table2 )
;

or

INSERT into table2 (table1_id, column3, column4)
SELECT t1.id, s.str, s.str
FROM table1 AS t1
CROSS JOIN (SELECT "fizz" AS str UNION SELECT "buzz" UNION SELECT "hello world") AS s
WHERE t1.thing1 = true
    AND NOT EXISTS (
           SELECT * 
           FROM table2 AS t2 
           WHERE t2.table1_id = t1.id AND t2.column3 = s.str
        )
;

If Sql Server, the union subquery (including it's surrounding parenthesis and alias) can be replaced with (VALUES ('fizz'), ('buzz'), ('hello word')) AS s(str) .