MYSQL - 在 INSERT 语句中使用函数

Question

I am moving data from Spreadsheets to MySQL. So we know that in Spreadsheets usually there is no ID, instead, just text.

City;Country;...
New York;USA;...
Berlim;Germany;...
Munich,Germany,...

With that in mind, let's consider two tables:

Country : [ID, name]

City : [ID , country (FK) , name]

I dont want to create several countries with the same name -- but I want to use the existing one. Perfect, so, let's add a FUNCTION in the INSERT state that searches, insert (if needed) and return the Country ID.

So I created a Function to FIRST assess whether the Country exists if not then create a country

getCountry (parameter IN strCountry varchar(100))

BEGIN
SELECT ID INTO @id from `country` WHERE country.country = strCountry ;
IF (@id is NULL OR @id= 0) THEN
    INSERT INTO `country` (country) VALUES (strCountry);
    if (ROW_COUNT()>0) THEN
        SET @id = LAST_INSERT_ID();
    else
        SET @id = NULL;
    END IF;
END IF ;
RETURN @id;
END

And then I have DOZENS OF THOUSANDS of INSERTS such as

INSERT INTO city (name, country) VALUES ('name of the city', getCountry('new or existing one'));

The Function works well when executed alone, such as

SELECT getCountry('Aruba');

However, when I execute that in that VERY LONG SQL (22K+ rows) then it does not work.... it uses basically the latest ID that was created BEFORE starting the execution. Maybe I should "wait" the function execute and return a proper result? But How?

What am I doing wrong?

Answer 1

Instead of function why not use a Stored Procedure, then the procedure will process the checking and insertion.

https://www.mysqltutorial.org/getting-started-with-mysql-stored-procedures.aspx

DELIMITER $$
CREATE PROCEDURE `sp_city_add`(in p_city varchar(100), in p_country varchar(100))
BEGIN

DECLARE country_id INT;

IF (SELECT COUNT(1) FROM country WHERE country.country = p_country) = 0 THEN
    INSERT INTO country (country) VALUE (p_country);

    SET country_id = LAST_INSERT_ID();
ELSE
    SELECT ID INTO country_id FROM country WHERE country.country = p_country;
END IF;

INSERT INTO city (name, country) VALUES (p_city, country_id);

END$$
DELIMITER ;

And if you want to execute a procedure

CALL sp_city_add('Bogota', 'Colombia');
CALL sp_city_add('Phnom Penh', 'Cambodia');
CALL sp_city_add('Yaounde', 'Cameroon');
CALL sp_city_add('Ottawa', 'Canada');
CALL sp_city_add('Santiago', 'Chile');
CALL sp_city_add('Beijing', 'China');
CALL sp_city_add('Bogotá', 'Colombia');
CALL sp_city_add('Moroni', 'Comoros');

You can also add a condition to check if the city and country exists to prevent duplicate entry.

Answer 2

I can't find any documentation of it, but maybe there's a conflict when you do an INSERT in a function that's called during another INSERT . So try splitting them up using a variable:

SELECT @country := getCountry('new or existing one');
INSERT INTO city (name, country) VALUES ('name of the city', @country);

Answer 3

Using the idea of @Barman, PLUS adding COMMIT to each row I could solve that:

SELECT @id := getCountry("Colombia");INSERT into city ( city, country) VALUES ('Bogota',@id);COMMIT;
SELECT @id := getCountry("Colombia");INSERT into city ( city, country) VALUES ('Medelin',@id);COMMIT;
SELECT @id := getCountry("Brazil");INSERT into city ( city, country) VALUES ('Medelin',@id);COMMIT;
SELECT @id := getCountry("Brazil");INSERT into city ( city, country) VALUES ('Sao Paulo',@id);COMMIT;
SELECT @id := getCountry("Brazil");INSERT into city ( city, country) VALUES ('Curitiba',@id);COMMIT;
SELECT @id := getCountry("USA");INSERT into city ( city, country) VALUES ('Boston',@id);COMMIT;
SELECT @id := getCountry("USA");INSERT into city ( city, country) VALUES ('DallaS',@id);COMMIT;

Without the COMMIT at the end of each row, MySQL was not calculating the variable anymore, instead, just throwing some last result it collected.