fix incorrect column name in Index Join (#18305) (#18306)

explain-joins.md

@@ -70,7 +70,7 @@ Index join is efficient in memory usage, but might be slower to execute than oth
 SELECT * FROM t1 INNER JOIN t2 ON t1.id=t2.t1_id WHERE t1.pad1 = 'value' and t2.pad1='value';
 ```
 
-In an inner join operation, TiDB implements join reordering and might access either `t1` or `t2` first. Assume that TiDB selects `t1` as the first table to apply the `build` step, and then TiDB is able to filter on the predicate `t1.col = 'value'` before probing the table `t2`. The filter for the predicate `t2.col='value'` will be applied on each probe of table `t2`, which might be less efficient than other join methods.
+In an inner join operation, TiDB implements join reordering and might access either `t1` or `t2` first. Assume that TiDB selects `t1` as the first table to apply the `build` step, and then TiDB is able to filter on the predicate `t1.pad1 = 'value'` before probing the table `t2`. The filter for the predicate `t2.pad1='value'` will be applied on each probe of table `t2`, which might be less efficient than other join methods.
 
 Index join is effective if the build side is small and the probe side is pre-indexed and large. Consider the following query where an index join performs worse than a hash join and is not chosen by the SQL Optimizer: