Error Code: 1172. Result consisted of more than one row [MySQL]

Question

it is my first time to create a stored procedure in mysql.

What it does is,

first- get count of all records

second- loop through that table 1 by 1

third- compare each entry if it is a duplicate

fourth- insert duplicate in a temporary table

last- display duplicates

It is working properly on 100-200 entries BUT on bigger records up to 500+ (sometimes 25k) it throws a message

Error Code: 1172. Result consisted of more than one row

I have googled this issue but none of them (answers) help me to solve my problem.

Please take a look on my script

BEGIN

DECLARE n INT DEFAULT 0;
DECLARE i INT DEFAULT 0;

DECLARE i_sku VARCHAR(255);
DECLARE i_concatenated_attributes MEDIUMTEXT;

DECLARE f_sku VARCHAR(255);
DECLARE f_offer_type VARCHAR(255);
DECLARE f_name VARCHAR(255);
DECLARE f_product_owner VARCHAR(255);
DECLARE f_listing_city VARCHAR(255);
DECLARE f_listing_area VARCHAR(255);
DECLARE f_price DOUBLE;
DECLARE f_bedrooms INT;
DECLARE f_building_size INT;
DECLARE f_land_size INT;
DECLARE f_concatenated_attributes MEDIUMTEXT;
DECLARE f_duplicate_percentage INT;

SELECT COUNT(*) FROM unit_temp_listing INTO n;
CREATE TEMPORARY TABLE IF NOT EXISTS temp_temp (dup_sku VARCHAR(255), dup_percentage INT, attribs MEDIUMTEXT);
SET i=0;
WHILE i<n DO 
    -- Get all unit listings (one by one)
    SELECT
    sku, concat_ws(',',offer_type,name,product_owner,listing_city,listing_area,price,ifnull(bedrooms,0),ifnull(building_size,0),ifnull(land_size,0)) as concatenated_attributes
INTO i_sku, i_concatenated_attributes
FROM unit_temp_listing
limit 1 offset i;
-- Compare one by one (sadla)
SELECT
    f.sku, f.offer_type, f.name, f.product_owner, f.listing_city, f.listing_area, f.price, f.bedrooms, f.building_size, f.land_size, 
    levenshtein_ratio(concat_ws(',',f.offer_type,f.name,f.product_owner,f.listing_city,f.listing_area,f.price,ifnull(f.bedrooms,0),ifnull(f.building_size,0),ifnull(f.land_size,0)),i_concatenated_attributes) as f_duplicate_percentage,
    concat_ws(',',f.offer_type,f.name,f.product_owner,f.listing_city,f.listing_area,f.price,ifnull(f.bedrooms,0),ifnull(f.building_size,0),ifnull(f.land_size,0)) as fconcatenated_attributes
INTO f_sku, f_offer_type, f_name, f_product_owner, f_listing_city, f_listing_area, f_price, f_bedrooms, f_building_size, f_land_size, f_duplicate_percentage, f_concatenated_attributes
FROM unit_temp_listing f
WHERE substring(soundex(concat_ws(',',offer_type,name,product_owner,listing_city,listing_area,price,ifnull(bedrooms,0),ifnull(building_size,0),ifnull(land_size,0))),1,10) = substring(soundex(i_concatenated_attributes),1,10) 
    AND levenshtein_ratio(concat_ws(',',offer_type,name,product_owner,listing_city,listing_area,price,ifnull(bedrooms,0),ifnull(building_size,0),ifnull(land_size,0)),i_concatenated_attributes) > 90
    AND f.sku != i_sku;
-- INSERT duplicates
IF(f_sku IS NOT NULL) THEN
    INSERT INTO temp_temp (dup_sku, dup_percentage, attribs) VALUES (f_sku, f_duplicate_percentage, f_concatenated_attributes);
    SET f_sku = null;
    SET f_duplicate_percentage = null;
    SET f_concatenated_attributes = null;
END IF;
SET i = i + 1;
END WHILE;
SELECT * FROM temp_temp;
DROP TABLE temp_temp;
End

What is the problem?

Answer 1

Hello to my fellow Developers out there I already solved my issue and I want to share it here.

The issue was, my SECOND SELECT statement inside the WHILE loop was returning multiple rows. I tried using CURSOR but I still got the error message. So I tried to put that second SELECT statement of mine inside the INSERT statement like this

INSERT INTO table_name (columns, ...) SELECT_STATEMENT

and then, problem was solved! But if anyone here have an idea to optimize my query please do help me. I have to process 20k+ records but because of time of execution took too long, I only settle for 500 for 15-20 mins.

Thank you for the 18 views (at the time of writing).

Happy coding!