MySQL Insert from 2 source tables to one destination table - mysql

Question

I am having issues inserting Id fields from two tables into a single record in a third table.
mysql> describe ing_titles;
+----------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+----------------+
| ID_Title | int(10) unsigned | NO | PRI | NULL | auto_increment |
| title | varchar(64) | NO | UNI | NULL | |
+----------+------------------+------+-----+---------+----------------+
2 rows in set (0.22 sec)
mysql> describe ing_categories;
+-------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+------------------+------+-----+---------+----------------+
| ID_Category | int(10) unsigned | NO | PRI | NULL | auto_increment |
| category | varchar(64) | NO | UNI | NULL | |
+-------------+------------------+------+-----+---------+----------------+
2 rows in set (0.02 sec)
mysql> describe ing_title_categories;
+-------------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+------------------+------+-----+---------+----------------+
| ID_Title_Category | int(10) unsigned | NO | PRI | NULL | auto_increment |
| ID_Title | int(10) unsigned | NO | MUL | NULL | |
| ID_Category | int(10) unsigned | NO | MUL | NULL | |
+-------------------+------------------+------+-----+---------+----------------+
3 rows in set (0.04 sec)
Let's say the data from the tables is:
mysql> select * from ing_titles;
+----------+-------------------+
| ID_Title | title |
+----------+-------------------+
| 3 | Chicken |
| 2 | corn |
| 1 | Fettucini Alfredo |
+----------+-------------------+
3 rows in set (0.00 sec)
mysql> select * from ing_categories;
+-------------+----------+
| ID_Category | category |
+-------------+----------+
| 1 | Dinner |
| 3 | Meat |
| 2 | Veggie |
+-------------+----------+
3 rows in set (0.00 sec)
I want to insert into ing_title_categories the record "corn, Veggie" or where ID_Title = 2 and ID_Category = 2.
Here's what I tried:
INSERT INTO ing_title_categories (ID_Title, ID_Category)
SELECT ing_titles.ID_Title, ing_categories.ID_Category
FROM ing_title_categories
LEFT JOIN ing_titles ON ing_title_categories.ID_Title=ing_titles.ID_Title
LEFT JOIN ing_categories ON ing_title_categories.ID_Category=ing_categories.ID_Category
WHERE (ing_titles.ID_Title=2) AND (ing_categories.ID_Category = 2);
There is no data inserted into the table ing_title_categories, and here is the reply from MySQL:
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
What is the correct syntax for inserting the ing_titles.ID_Title and ing_categories.ID_Category into the table ing_titles_categories?
Please, no PHP or Python examples. Use SQL that I can copy and paste into the MySQL prompt. I will be adding this to a C++ program, not PHP, JavaScript or Python.
Edit 1:
The ing_title_categories.ID_Title and ing_title_categories.ID_Category are foreign keys into the other tables.

Answer 1

INSERT INTO
ing_title_categories (ID_Title, ID_Category)
SELECT
ing_titles.ID_Title, ing_categories.ID_Category
FROM
ing_titles, ing_categories
WHERE
ing_titles.ID_Title = ing_categories.ID_Category AND
ing_titles.ID_Title = 2 AND ing_categories.ID_Category = 2;
SQL Fiddle demo

Answer 2

After taking advice from #DrewPierce and #KaiserM11, here is the MySQL sequence:
mysql> INSERT INTO ing_title_categories (ID_Title, ID_Category)
-> SELECT
-> ing_titles.ID_Title,
-> ing_categories.ID_Category
-> FROM ing_titles, ing_categories
-> where (ing_titles.ID_Title = 2) AND (ing_categories.ID_Category = 2)
-> ;
Query OK, 1 row affected (0.07 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> select * from ing_title_categories;
+-------------------+----------+-------------+
| ID_Title_Category | ID_Title | ID_Category |
+-------------------+----------+-------------+
| 17 | 2 | 2 |
+-------------------+----------+-------------+
1 row in set (0.00 sec)

Answer 3

In this case, only possible way I see is using a UNION query like
INSERT INTO ing_title_categories (ID_Title, ID_Category)
SELECT Title, NULL
FROM ing_title WHERE ID_Title = 2
UNION
SELECT NULL, category
FROM ing_categories
WHERE ID_Category = 2
(OR)
You can change your table design and use an AFTER INSERT trigger to perform the same in one go.
EDIT:
If you can change your table design to something like below (No need of that extra chaining table)
ing_titles(ID_Title int not null auto_increment PK, title varchar(64) not null);
ing_categories( ID_Category int not null auto_increment PK,
category varchar(64) not null,
ing_titles_ID_Title int not null,
FOREIGN KEY (ing_titles_ID_Title)
REFERENCES ing_titles(ID_Title));
Then you can use a AFTER INSERT trigger and do the insertion like
DELIMITER //
CREATE TRIGGER ing_titles_after_insert
AFTER INSERT
ON ing_titles FOR EACH ROW
BEGIN
-- Insert record into ing_categories table
INSERT INTO ing_categories
( category,
ing_titles_ID_Title)
VALUES
('Meat' NEW.ID_Title);
END; //
DELIMITER ;