MDEV-462: SHOW EXPLAIN: Assertion `table_list->table' fails in find_field_in_table_ref ...

- Only allow basic constants as SHOW EXPLAIN arguments.

mysql-test/r/show_explain.result

@@ -7,7 +7,7 @@ insert into t1 select A.a + 10*B.a + 100*C.a from t0 A, t0 B, t0 C;
 alter table t1 add b int, add c int, add filler char(32);
 update t1 set b=a, c=a, filler='fooo';
 alter table t1 add key(a), add key(b);
-show explain for 2*1000*1000*1000;
+show explain for 2000000000;
 ERROR HY000: Unknown thread id: 2000000000
 show explain for (select max(a) from t0);
 ERROR HY000: You may only use constant expressions in this statement
@@ -1069,5 +1069,10 @@ a
 2
 set debug_dbug='';
 set names default;
+#
+# MDEV-462: SHOW EXPLAIN: Assertion `table_list->table' fails in find_field_in_table_ref if FOR contains a non-numeric value
+#
+show explain for foo;
+ERROR HY000: You may only use constant expressions in this statement
 # End
 drop table t0;

mysql-test/t/show_explain.test

@@ -43,7 +43,7 @@ alter table t1 add key(a), add key(b);
 # Try killing a non-existent thread
 # 
 --error ER_NO_SUCH_THREAD
-show explain for 2*1000*1000*1000;
+show explain for 2000000000;
 
 --error ER_SET_CONSTANTS_ONLY
 show explain for (select max(a) from t0);
@@ -1105,5 +1105,11 @@ reap;
 set debug_dbug='';
 set names default;
 
+--echo #
+--echo # MDEV-462: SHOW EXPLAIN: Assertion `table_list->table' fails in find_field_in_table_ref if FOR contains a non-numeric value
+--echo #
+--error ER_SET_CONSTANTS_ONLY 
+show explain for foo;
+
 --echo # End
 drop table t0;

sql/sql_parse.cc

@@ -2159,7 +2159,8 @@ mysql_execute_command(THD *thd)
     }
 
     Item **it= lex->value_list.head_ref();
-    if ((!(*it)->fixed && (*it)->fix_fields(lex->thd, it)) || 
+    if (!(*it)->basic_const_item() ||
+        (!(*it)->fixed && (*it)->fix_fields(lex->thd, it)) || 
         (*it)->check_cols(1))
     {
       my_message(ER_SET_CONSTANTS_ONLY, ER(ER_SET_CONSTANTS_ONLY),