Use MySQL column names in MySQL queries.

The query for concurrency-support didn't get the memo that we should ignore
PostgreSQL identifier-case when querying the source MySQL database. Fix the
query string to include column names as given by the MySQL catalogs.

In bug report #703, the problem is found in PostgreSQL queries. This has
been fixed before already. Trying to reproduce the bug produced an error in
the concurrency-support query instead, so let's fix this one.

Fix #703.

src/sources/mysql/mysql.lisp

@@ -54,7 +54,9 @@
         ;; the table has a primary key over a integer data type we are able
         ;; to generate WHERE clause and range index scans.
         (with-connection (*connection* (source-db mysql))
-          (let* ((col pcol)
+          (let* ((col (mysql-column-name
+                       (nth (position coldef (table-column-list (target mysql)))
+                            (fields mysql))))
                  (sql (format nil "select min(`~a`), max(`~a`) from `~a`"
                               col col (table-source-name (source mysql)))))
             (destructuring-bind (min max)

test/mysql/my.load

@@ -5,7 +5,8 @@ load database
 
  WITH concurrency = 2,
       multiple readers per thread,
-      rows per range = 50000
+      rows per range = 50000,
+      quote identifiers
 
  ALTER SCHEMA 'pgloader' RENAME TO 'mysql'
 

test/mysql/my.sql

@@ -100,6 +100,13 @@ create table bits
 
 insert into bits(bool) values(0b00), (0b01);
 
+/*
+ * https://github.com/dimitri/pgloader/issues/703
+ */
+create table `CamelCase` (
+ `validSizes` varchar(12)
+);
+
 CREATE TABLE `fcm_batches` (
   `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
   `raw_payload` mediumtext COLLATE utf8_unicode_ci,