使用子字符串后，mysql quert中出现多个警告

Question

I have simple EAV like database which has 3 tables: products, attributes, attribute_values.

I am using below code to find all products that have attribute 'length' and then I am using substring function to get rid of 'inch' and after that I am using between to get all products that have 'length' between 0 and 5.

SELECT products.name,products.id
FROM products
JOIN attribute_value_product on products.id = attribute_value_product.product_id
JOIN attribute_values on attribute_value_product.attribute_value_id = attribute_values.id
JOIN attributes on attribute_values.attribute_id = attributes.id AND attributes.name = 'length'
WHERE substring_index(attribute_values.value,'inch',1) + 0 BETWEEN 0 AND 5

Everything works fine however I am getting plenty of warnings:

Warning: #1292 Truncated incorrect DOUBLE value: 'black'    
Warning: #1292 Truncated incorrect DOUBLE value: 'phat farm'    
Warning: #1292 Truncated incorrect DOUBLE value: '2 kg'    
Warning: #1292 Truncated incorrect DOUBLE value: 'roca wear'

it looks to me like that substring is going through all attribute_values in the database, even those that are not referring to attribute 'length' - is it possible to change that ?

Answer 1

The SUBSTRING_INDEX() function returns a substring of a string Then your where condition

WHERE substring_index(attribute_values.value,'inch',1) + 0 BETWEEN 0 AND 5

is wrong because you are try adding a string to a number

could be you are looking for the left of the substr

WHERE length(substring_index(attribute_values.value,'inch',1)) + 0 BETWEEN 0 AND 5

NOTE: if the delimiter ('inch') is not foudn then the function return all the string so you should check

Seems you want read the previous part :

The SUBSTRING_INDEX() function returns a substring of a string

of if you want the numeric part of the string before the 'inch' you could try uing cast

WHERE cast(trim(substring_index(attribute_values.value,'inch',1)) AS UNSIGNED ) + 0 
            BETWEEN 0 AND 5

and for avoid the warning for not numeric content you could try this where condition

WHERE (case when substring_index(attribute_values.value,'inch',1) = attribute_values.value 
 then 1000 
 else cast(trim(substring_index(attribute_values.value,'inch',1)) AS UNSIGNED ) end )
 BETWEEN 0 AND 5