dict_load_column_low(): Initialize pos. Improve documentation.

Approved by Jimmy Yang.

storage/innobase/dict/dict0load.c

@@ -782,12 +782,13 @@ const char*
 dict_load_column_low(
 /*=================*/
 	dict_table_t*	table,		/*!< in/out: table, could be NULL
-					if we just polulate a dict_column_t
+					if we just populate a dict_column_t
 					struct with information from
 					a SYS_COLUMNS record */
 	mem_heap_t*	heap,		/*!< in/out: memory heap
 					for temporary storage */
-	dict_col_t*	column,		/*!< out: dict_column_t to fill */
+	dict_col_t*	column,		/*!< out: dict_column_t to fill,
+					or NULL if table != NULL */
 	dulint*		table_id,	/*!< out: table id */
 	const char**	col_name,	/*!< out: column name */
 	const rec_t*	rec)		/*!< in: SYS_COLUMNS record */
@@ -800,6 +801,8 @@ dict_load_column_low(
 	ulint		col_len;
 	ulint		pos;
 
+	ut_ad(table || column);
+
 	if (UNIV_UNLIKELY(rec_get_deleted_flag(rec, 0))) {
 		return("delete-marked record in SYS_COLUMNS");
 	}
@@ -827,9 +830,9 @@ err_len:
 		goto err_len;
 	}
 
-	if (!table) {
 	pos = mach_read_from_4(field);
-	} else if (UNIV_UNLIKELY(table->n_def != mach_read_from_4(field))) {
+
+	if (UNIV_UNLIKELY(table && table->n_def != pos)) {
 		return("SYS_COLUMNS.POS mismatch");
 	}
 

storage/innobase/include/dict0load.h

@@ -109,7 +109,8 @@ dict_load_column_low(
 					a SYS_COLUMNS record */
 	mem_heap_t*	heap,		/*!< in/out: memory heap
 					for temporary storage */
-	dict_col_t*	column,		/*!< out: dict_column_t to fill */
+	dict_col_t*	column,		/*!< out: dict_column_t to fill,
+					or NULL if table != NULL */
 	dulint*		table_id,	/*!< out: table id */
 	const char**	col_name,	/*!< out: column name */
 	const rec_t*	rec);		/*!< in: SYS_COLUMNS record */