MDEV-23645: Optimizer trace: print conditions after substitute_for_best_equal_field

Print the conditions for WHERE, HAVING, and ON.

mysql-test/main/opt_trace.test

@@ -727,4 +727,57 @@ select
 
 drop table t1,t2,t3;
 
+--echo #
+--echo # MDEV-23645: Optimizer trace: print conditions after substitute_for_best_equal_field
+--echo #
+create table t1 (a int, b int, c int);
+insert into t1 values (1,1,1),(2,2,2);
+
+create table t2 as select * from t1;
+insert into t2 select * from t2;
+
+create table t3 as select * from t2;
+insert into t3 select * from t3;
+
+--echo # Check how HAVING is printed
+explain 
+select 
+  a,b, count(*)
+from t1
+where a=3
+group by b,b
+having a+b < 10;
+
+select
+  json_detailed(json_extract(trace, '$**.substitute_best_equal'))
+from
+  information_schema.optimizer_trace;
+
+--echo # Check ON expression
+explain 
+select 
+ *
+from t1 left join t2 on t2.a=t1.a and t2.a<3 
+where 
+  t1.b > 5555;
+
+select
+  json_detailed(json_extract(trace, '$**.substitute_best_equal'))
+from
+  information_schema.optimizer_trace;
+
+--echo # Check nested ON expression
+explain 
+select 
+ *
+from t1 left join (t2,t3) on t2.a=t1.a and t3.a=t2.a and t3.a + t2.a <1000
+where 
+  t1.b > 5555;
+select
+  json_detailed(json_extract(trace, '$**.substitute_best_equal'))
+from
+  information_schema.optimizer_trace;
+
+drop table t1,t2,t3;
+
 set optimizer_trace='enabled=off';

mysql-test/main/opt_trace_index_merge.result

@@ -229,9 +229,14 @@ explain select * from t1 where a=1 or b=1	{
           {
             "best_join_order": ["t1"]
           },
+          {
+            "substitute_best_equal": {
+              "condition": "WHERE",
+              "resulting_condition": "t1.a = 1 or t1.b = 1"
+            }
+          },
           {
             "attaching_conditions_to_tables": {
-              "original_condition": "t1.a = 1 or t1.b = 1",
               "attached_conditions_computation": [],
               "attached_conditions_summary": [
                 {

mysql-test/main/opt_trace_index_merge_innodb.result

@@ -234,9 +234,14 @@ explain select * from t1 where pk1 != 0  and key1 = 1	{
           {
             "best_join_order": ["t1"]
           },
+          {
+            "substitute_best_equal": {
+              "condition": "WHERE",
+              "resulting_condition": "t1.key1 = 1 and t1.pk1 <> 0"
+            }
+          },
           {
             "attaching_conditions_to_tables": {
-              "original_condition": "t1.key1 = 1 and t1.pk1 <> 0",
               "attached_conditions_computation": [],
               "attached_conditions_summary": [
                 {

mysql-test/main/opt_trace_security.result

@@ -117,7 +117,6 @@ select * from db1.t1	{
           },
           {
             "attaching_conditions_to_tables": {
-              "original_condition": null,
               "attached_conditions_computation": [],
               "attached_conditions_summary": [
                 {
@@ -240,7 +239,6 @@ select * from db1.v1	{
           },
           {
             "attaching_conditions_to_tables": {
-              "original_condition": null,
               "attached_conditions_computation": [],
               "attached_conditions_summary": [
                 {

sql/opt_trace.cc

@@ -595,6 +595,18 @@ void Json_writer::add_table_name(const TABLE *table)
 }
 
 
+void trace_condition(THD * thd, const char *name, const char *transform_type,
+                    Item *item, const char *table_name)
+{
+  Json_writer_object trace_wrapper(thd);
+  Json_writer_object trace_cond(thd, transform_type);
+  trace_cond.add("condition", name);
+  if (table_name)
+    trace_cond.add("attached_to", table_name);
+  trace_cond.add("resulting_condition", item);
+}
+
+
 void add_table_scan_values_to_trace(THD *thd, JOIN_TAB *tab)
 {
   DBUG_ASSERT(thd->trace_started());

sql/opt_trace.h

@@ -108,6 +108,10 @@ void print_final_join_order(JOIN *join);
 void print_best_access_for_table(THD *thd, POSITION *pos,
                                  enum join_type type);
 
+void trace_condition(THD * thd, const char *name, const char *transform_type,
+                    Item *item, const char *table_name= nullptr);
+
+
 /*
   Security related (need to add a proper comment here)
 */

sql/sql_select.cc

@@ -2408,6 +2408,10 @@ int JOIN::optimize_stage2()
       DBUG_RETURN(1);
     }
     conds->update_used_tables();
+
+    if (unlikely(thd->trace_started()))
+      trace_condition(thd, "WHERE", "substitute_best_equal", conds);
+
     DBUG_EXECUTE("where",
                  print_where(conds,
                              "after substitute_best_equal",
@@ -2424,7 +2428,12 @@ int JOIN::optimize_stage2()
       DBUG_RETURN(1);
     }
     if (having)
+    {
       having->update_used_tables();
+      if (unlikely(thd->trace_started()))
+        trace_condition(thd, "HAVING", "substitute_best_equal", having);
+    }
+
     DBUG_EXECUTE("having",
                  print_where(having,
                              "after substitute_best_equal",
@@ -2451,6 +2460,11 @@ int JOIN::optimize_stage2()
         DBUG_RETURN(1);
       }
       (*tab->on_expr_ref)->update_used_tables();
+      if (unlikely(thd->trace_started()))
+      {
+        trace_condition(thd, "ON expr", "substitute_best_equal",
+                        (*tab->on_expr_ref), tab->table->alias.c_ptr());
+      }
     }
   }
 
@@ -11479,7 +11493,6 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
     */
     Json_writer_object trace_wrapper(thd);
     Json_writer_object trace_conditions(thd, "attaching_conditions_to_tables");
-    trace_conditions.add("original_condition", cond);
     Json_writer_array trace_attached_comp(thd,
                                         "attached_conditions_computation");
     uint i;