new method to detect commands where all VIEWs should be temporary tables (BUG#4803)

mysql-test/r/view.result:
  Showing VIEW with VIEWs in subquery
mysql-test/t/view.test:
  Showing VIEW with VIEWs in subquery
sql/sql_lex.cc:
  new method to detect commands where all VIEWs should be temporary tables
sql/sql_lex.h:
  new method to detect commands where all VIEWs should be temporary tables
sql/sql_view.cc:
  new method to detect commands where all VIEWs should be temporary tables
  debug output added

mysql-test/r/view.result

@@ -1083,3 +1083,12 @@ count(*)
 2
 drop view v1;
 drop table t1;
+create table t1 (a int);
+create table t2 (a int);
+create view v1 as select a from t1;
+create view v2 as select a from t2 where a in (select a from v1);
+show create view v2;
+Table	Create Table
+v2	CREATE VIEW test.v2 AS select `test`.`t2`.`a` AS `a` from `test`.`t2` where `a` in (select `v1`.`a` AS `a` from `test`.`v1`)
+drop view v2, v1;
+drop table t1, t2;

mysql-test/t/view.test

@@ -1027,3 +1027,14 @@ insert into t1 values (null);
 select * from v1;
 drop view v1;
 drop table t1;
+
+#
+# Showing VIEW with VIEWs in subquery
+#
+create table t1 (a int);
+create table t2 (a int);
+create view v1 as select a from t1;
+create view v2 as select a from t2 where a in (select a from v1);
+show create view v2;
+drop view v2, v1;
+drop table t1, t2;

sql/sql_lex.cc

@@ -1546,7 +1546,7 @@ bool st_lex::can_be_merged()
 }
 
 /*
-  check if command can use VIEW with MERGE algorithm
+  check if command can use VIEW with MERGE algorithm (for top VIEWs)
 
   SYNOPSIS
     st_lex::can_use_merged()
@@ -1576,6 +1576,29 @@ bool st_lex::can_use_merged()
   }
 }
 
+/*
+  check if command can't use merged views in any part of command
+
+  SYNOPSIS
+    st_lex::can_not_use_merged()
+
+  RETURN
+    FALSE - command can't use merged VIEWs
+    TRUE  - VIEWs with MERGE algorithms can be used
+*/
+
+bool st_lex::can_not_use_merged()
+{
+  switch (sql_command)
+  {
+  case SQLCOM_CREATE_VIEW:
+  case SQLCOM_SHOW_CREATE:
+    return TRUE;
+  default:
+    return FALSE;
+  }
+}
+
 /*
   Detect that we need only table structure of derived table/view
 

sql/sql_lex.h

@@ -749,6 +749,7 @@ typedef struct st_lex
 
   bool can_be_merged();
   bool can_use_merged();
+  bool can_not_use_merged();
   bool only_view_structure();
 } LEX;
 

sql/sql_view.cc

@@ -659,7 +659,8 @@ mysql_make_view(File_parser *parser, TABLE_LIST *table)
     if (table->algorithm != VIEW_ALGORITHM_TMEPTABLE &&
 	lex->can_be_merged() &&
         (table->select_lex->master_unit() != &old_lex->unit ||
-         old_lex->can_use_merged()))
+         old_lex->can_use_merged()) &&
+        !old_lex->can_not_use_merged())
     {
       /*
         TODO: support multi tables substitutions
@@ -672,6 +673,7 @@ mysql_make_view(File_parser *parser, TABLE_LIST *table)
       DBUG_ASSERT(view_table != 0);
 
       table->effective_algorithm= VIEW_ALGORITHM_MERGE;
+      DBUG_PRINT("info", ("algorithm: MERGE"));
       table->updatable= (table->updatable_view != 0);
 
       if (old_next)
@@ -701,6 +703,7 @@ mysql_make_view(File_parser *parser, TABLE_LIST *table)
     }
 
     table->effective_algorithm= VIEW_ALGORITHM_TMEPTABLE;
+    DBUG_PRINT("info", ("algorithm: TEMPORARY TABLE"));
     lex->select_lex.linkage= DERIVED_TABLE_TYPE;
     table->updatable= 0;