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  1. MariaDB Server
  2. MDEV-30539

EXPLAIN EXTENDED: no message with queries for DML statements

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    Description

      For the following query with SELECT:

      select * 
       from v1,t3
      where
        v1.c2 = t3.c2 and 
        v1.c2 in (select max(c2) from t2 where c3 = v1.c3)
                  and v1.c1 < 10 and
                  v1.c1 in (select c1 from v2);
      

      EXPLAIN EXTENDED produces messages:

      Warnings:
      Note	1276	Field or reference 'v1.c3' of SELECT #2 was resolved in SELECT #1
      Note	1003	/* select#1 */ select `test`.`t1`.`c1` AS `c1`,`test`.`t1`.`c2` AS `c2`,`test`.`t1`.`c3` AS `c3`,`test`.`t3`.`c1` AS `c1`,`test`.`t3`.`c2` AS `c2`,`test`.`t3`.`c3` AS `c3` from `test`.`t1` semi join (`test`.`t2`) join `test`.`t3` where `test`.`t1`.`c2` = 2 and `test`.`t3`.`c2` = 2 and `test`.`t2`.`c2` = 2 and <expr_cache><2,`test`.`t1`.`c3`>(<in_optimizer>(2,<exists>(/* select#2 */ select max(`test`.`t2`.`c2`) from `test`.`t2` where `test`.`t2`.`c3` = `test`.`t1`.`c3` having <cache>(`test`.`t1`.`c2`) = <ref_null_helper>(max(`test`.`t2`.`c2`))))) and `test`.`t1`.`c1` < 10
      

      For the queries with DELETE and UPDATE based on previous SELECT:

      delete
       from v1
       using v1,t3
      where
        v1.c2 = t3.c2 and 
        v1.c2 in (select max(c2) from t2 where c3 = v1.c3)
                  and v1.c1 < 10 and
                  exists (select 'X' from v2 where c1 = v1.c1);
      

      update v1,t3
      set v1.c1 = 15
      where
        v1.c2 = t3.c2 and 
        v1.c2 in (select max(c2) from t2 where c3 = v1.c3)
                  and v1.c1 < 10 and
                  exists (select 'X' from v2 where c1 = v1.c1);
      

      EXPLAIN EXTENDED does not produce message with query after optimization :

      Warnings:
      Note	1276	Field or reference 'v1.c3' of SELECT #2 was resolved in SELECT #1
      Note	1276	Field or reference 'v1.c1' of SELECT #3 was resolved in SELECT #1
      

      Problem with plan in this case will be fixed in MDEV-30538

      MTR test case:

      --source include/have_innodb.inc
       
      create table t1 (c1 integer, c2 integer, c3 integer) engine=innodb;
      insert into t1(c1,c2,c3)
      values (1,1,1),(1,2,2),(1,3,3),
      (2,1,4),(2,2,5),(2,3,6),
      (2,4,7),(2,5,8);
      create view v1 as select * from t1 where c2=2;
      create index t1_c2 on t1 (c2);
      analyze table t1 persistent for all;
       
      create table t2 (c1 integer, c2 integer, c3 integer) engine=innodb;
      insert into t2(c1,c2,c3)
      values (1,1,1),(1,2,2),(1,3,3),
      (2,1,4),(2,2,5),(2,3,6),
      (2,4,7),(2,5,8);
      create view v2 as select * from t2 where c2=2;
      create index t2_c2 on t2 (c2);
      analyze table t2 persistent for all;
       
      create table t3 (c1 integer, c2 integer, c3 integer) engine=innodb;
      insert into t3(c1,c2,c3)
      values (1,1,1),(1,2,2),(1,3,3),
      (2,1,4),(2,2,5),(2,3,6),
      (2,4,7),(2,5,8);
      analyze table t3 persistent for all;
       
      EXPLAIN  EXTENDED
      select * 
       from v1,t3
      where
        v1.c2 = t3.c2 and 
        v1.c2 in (select max(c2) from t2 where c3 = v1.c3)
                  and v1.c1 < 10 and
                  v1.c1 in (select c1 from v2);
       
       
      EXPLAIN EXTENDED  
      delete
       from v1
       using v1,t3
      where
        v1.c2 = t3.c2 and 
        v1.c2 in (select max(c2) from t2 where c3 = v1.c3)
                  and v1.c1 < 10 and
                  exists (select 'X' from v2 where c1 = v1.c1);
       
      EXPLAIN EXTENDED  
      update v1,t3
      set v1.c1 = 15
      where
        v1.c2 = t3.c2 and 
        v1.c2 in (select max(c2) from t2 where c3 = v1.c3)
                  and v1.c1 < 10 and
                  exists (select 'X' from v2 where c1 = v1.c1);
       
      drop view v1, v2;
      drop table t1, t2, t3;
      

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              igor Igor Babaev
              lstartseva Lena Startseva
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                Created:
                Updated:
                Resolved:

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