[IMP] account: improved join

Joining on a case is far to be optimal. doing 3 left joins and a coalesce is faster.
partner_id is a required field in res.partner.bank, but some migrated database have
records in res.partner.bank model without id. To keep existing behaviour, the third
join (the one on the name) is kept for backward compatibility.

closes odoo/odoo#29276

addons/account/models/reconciliation_widget.py

@@ -82,18 +82,12 @@ class AccountReconciliation(models.AbstractModel):
         query = '''
             SELECT
                 st_line.id                          AS id,
-                partner.id                          AS partner_id
+                COALESCE(p1.id,p2.id,p3.id)         AS partner_id
             FROM account_bank_statement_line st_line
             LEFT JOIN res_partner_bank bank         ON bank.id = st_line.bank_account_id OR bank.acc_number = st_line.account_number
-            LEFT JOIN res_partner partner           ON (
-                CASE WHEN st_line.partner_id IS NOT NULL THEN
-                    partner.id = st_line.partner_id
-                WHEN bank.partner_id IS NOT NULL THEN
-                    partner.id = bank.partner_id
-                ELSE
-                    partner.name ILIKE st_line.partner_name
-                END
-            )
+            LEFT JOIN res_partner p1 ON st_line.partner_id=p1.id
+            LEFT JOIN res_partner p2 ON bank.partner_id=p2.id
+            LEFT JOIN res_partner p3 ON p3.name ILIKE st_line.partner_name
             WHERE st_line.id IN %s
         '''
         params = [tuple(st_lines.ids)]