ext/pdo: Refactor do_fetch() when fetch mode is PDO::FETCH_COLUMN

This is one hell of a convoluted and bonker behaviour

Author: Girgias

ext/pdo/pdo_stmt.c

@@ -763,36 +763,35 @@ static bool do_fetch(pdo_stmt_t *stmt, zval *return_value, enum pdo_fetch_type h
 
 	/* When fetching a column we only do one value fetch, so handle it separately */
 	if (how == PDO_FETCH_COLUMN) {
-		int colno = stmt->fetch.column;
-
-		if ((flags & PDO_FETCH_GROUP) && stmt->fetch.column == -1) {
-			colno = 1;
+		int fetch_column_number = stmt->fetch.column;
+		int group_column_number = 0;
+
+		/* For an explicit column fetch with PDO_FETCH_GROUP, the group and fetch column is 1 */
+		if (stmt->fetch.column != -1) {
+			if (flags == PDO_FETCH_GROUP) {
+				group_column_number = 1;
+				fetch_column_number = 1;
+			}
+		} else {
+			if (flags == PDO_FETCH_GROUP || flags == PDO_FETCH_UNIQUE) {
+				fetch_column_number = 1;
+			}
 		}
 
-		if (colno < 0 ) {
+		if (fetch_column_number < 0 ) {
 			zend_value_error("Column index must be greater than or equal to 0");
 			return false;
 		}
 
-		if (colno >= stmt->column_count) {
+		if (fetch_column_number >= stmt->column_count) {
 			zend_value_error("Invalid column index");
 			return false;
 		}
 
-		if (flags == PDO_FETCH_GROUP && stmt->fetch.column == -1) {
-			fetch_value(stmt, return_value, 1, NULL);
-		} else if (flags == PDO_FETCH_GROUP && colno) {
-			fetch_value(stmt, return_value, 0, NULL);
-		} else {
-			fetch_value(stmt, return_value, colno, NULL);
-		}
+		fetch_value(stmt, return_value, fetch_column_number, NULL);
 
 		if (group_key) {
-			if (flags == PDO_FETCH_GROUP && stmt->fetch.column > 0) {
-				fetch_value(stmt, group_key, colno, NULL);
-			} else {
-				fetch_value(stmt, group_key, 0, NULL);
-			}
+			fetch_value(stmt, group_key, group_column_number, NULL);
 			convert_to_string(group_key);
 		}
 		return true;