I have a query that uses SUBSTRING() as a criteria:
SELECT p.name p_name,
pa.line1 p_line1,
pa.zip p_zip,
c.name c_name,
ca.line1 c_line1,
ca.zip c_zip
FROM bank b
JOIN import_bundle ib ON ib.bank_id = b.id
JOIN generic_import gi ON gi.import_bundle_id = ib.id
JOIN account_import ai ON ai.generic_import_id = gi.id
JOIN account a ON a.account_import_id = ai.id
JOIN account_address aa ON aa.account_id = a.id
JOIN address ca ON aa.address_id = ca.id
JOIN address pa ON pa.zip = ca.zip OR (pa.zip = ca.zip AND pa.line1 = ca.line1)
JOIN prospect p ON p.address_id = pa.id
JOIN customer c ON a.customer_id = c.id
WHERE b.name = 'M'
AND ib.active = 1
AND gi.active = 1
AND SUBSTRING(p.name, 1, 12) = SUBSTRING(c.name, 1, 12)
LIMIT 100
As you can see, it’s just comparing the first 12 characters of p.name and c.name. Unfortunately, adding this query to the WHERE clause makes my query unbearably slow. Are there any tricks out there to do this same comparison, or is my best bet to add another column to each table that contains the first 12 characters of the customer’s name? I hope it’s not the latter because that would be a lot of work and I’ll ultimately be doing several comparisons like this.
Add the extra columns and set up an update trigger to populate them automatically. Be sure to create indexes on the new columns, of course.