MDEV-6954: SET STATEMENT rand_seedX = ...FOR ... makes the next rand() to return 0

The variables now return real values. They can't be made usual variables because they do not have DEFAULT value.

mysql-test/r/set_statement.result

@@ -1122,10 +1122,6 @@ set statement autocommit=default for select 1;
 ERROR 42000: The system variable autocommit cannot be set in SET STATEMENT.
 set statement tx_isolation=default for select 1;
 ERROR 42000: The system variable tx_isolation cannot be set in SET STATEMENT.
-set statement rand_seed1=default for select 1;
-ERROR 42000: The system variable rand_seed1 cannot be set in SET STATEMENT.
-set statement rand_seed2=default for select 1;
-ERROR 42000: The system variable rand_seed2 cannot be set in SET STATEMENT.
 set statement skip_replication=default for select 1;
 ERROR 42000: The system variable skip_replication cannot be set in SET STATEMENT.
 set statement sql_log_off=default for select 1;
@@ -1214,3 +1210,13 @@ ERROR HY000: Unknown system variable 'non_existing'
 show errors;
 Level	Code	Message
 Error	1193	Unknown system variable 'non_existing'
+#
+# MDEV-6954: SET STATEMENT rand_seedX = ...FOR ... makes
+# the next rand() to return 0
+#
+set @rnd=1;
+# test that rand() is not always 0 after restoring rand_seed, rand_seed2...
+# @rnd should be 0
+select @rnd;
+@rnd
+0

mysql-test/suite/sys_vars/inc/sysvars_server.inc

@@ -25,6 +25,8 @@ select * from information_schema.system_variables
           'lower_case_file_system',
           'lower_case_table_names',
           'open_files_limit',
+          'rand_seed1',
+          'rand_seed2',
           'system_time_zone',
           'version_comment',
           'version_compile_machine', 'version_compile_os',
@@ -46,6 +48,8 @@ select VARIABLE_NAME, VARIABLE_SCOPE, VARIABLE_TYPE, VARIABLE_COMMENT,
           'lower_case_file_system',
           'lower_case_table_names',
           'open_files_limit',
+          'rand_seed1',
+          'rand_seed2',
           'system_time_zone',
           'version_comment',
           'version_compile_machine', 'version_compile_os',

mysql-test/suite/sys_vars/r/rand_seed1_basic.result

@@ -1,27 +1,30 @@
 select @@global.rand_seed1;
 ERROR HY000: Variable 'rand_seed1' is a SESSION variable
+set session rand_seed1=default;
+ERROR 42000: Variable 'rand_seed1' doesn't have a default value
+set session rand_seed1=10969771;
 select @@session.rand_seed1;
 @@session.rand_seed1
-0
+10969771
 show global variables like 'rand_seed1';
 Variable_name	Value
 show session variables like 'rand_seed1';
 Variable_name	Value
-rand_seed1	0
+rand_seed1	10969771
 select * from information_schema.global_variables where variable_name='rand_seed1';
 VARIABLE_NAME	VARIABLE_VALUE
 select * from information_schema.session_variables where variable_name='rand_seed1';
 VARIABLE_NAME	VARIABLE_VALUE
-RAND_SEED1	0
+RAND_SEED1	10969771
 set session rand_seed1=1;
 select @@session.rand_seed1;
 @@session.rand_seed1
-0
+1
 select * from information_schema.global_variables where variable_name='rand_seed1';
 VARIABLE_NAME	VARIABLE_VALUE
 select * from information_schema.session_variables where variable_name='rand_seed1';
 VARIABLE_NAME	VARIABLE_VALUE
-RAND_SEED1	0
+RAND_SEED1	1
 set global rand_seed1=1;
 ERROR HY000: Variable 'rand_seed1' is a SESSION variable and can't be used with SET GLOBAL
 set session rand_seed1=1.1;

mysql-test/suite/sys_vars/r/rand_seed2_basic.result

@@ -1,27 +1,30 @@
 select @@global.rand_seed2;
 ERROR HY000: Variable 'rand_seed2' is a SESSION variable
+set session rand_seed2=default;
+ERROR 42000: Variable 'rand_seed2' doesn't have a default value
+set session rand_seed2=10969771;
 select @@session.rand_seed2;
 @@session.rand_seed2
-0
+10969771
 show global variables like 'rand_seed2';
 Variable_name	Value
 show session variables like 'rand_seed2';
 Variable_name	Value
-rand_seed2	0
+rand_seed2	10969771
 select * from information_schema.global_variables where variable_name='rand_seed2';
 VARIABLE_NAME	VARIABLE_VALUE
 select * from information_schema.session_variables where variable_name='rand_seed2';
 VARIABLE_NAME	VARIABLE_VALUE
-RAND_SEED2	0
+RAND_SEED2	10969771
 set session rand_seed2=1;
 select @@session.rand_seed2;
 @@session.rand_seed2
-0
+1
 select * from information_schema.global_variables where variable_name='rand_seed2';
 VARIABLE_NAME	VARIABLE_VALUE
 select * from information_schema.session_variables where variable_name='rand_seed2';
 VARIABLE_NAME	VARIABLE_VALUE
-RAND_SEED2	0
+RAND_SEED2	1
 set global rand_seed2=1;
 ERROR HY000: Variable 'rand_seed2' is a SESSION variable and can't be used with SET GLOBAL
 set session rand_seed2=1.1;

mysql-test/suite/sys_vars/r/sysvars_server_embedded.result

@@ -15,6 +15,8 @@ variable_name not in (
 'lower_case_file_system',
 'lower_case_table_names',
 'open_files_limit',
+'rand_seed1',
+'rand_seed2',
 'system_time_zone',
 'version_comment',
 'version_compile_machine', 'version_compile_os',
@@ -3087,34 +3089,6 @@ NUMERIC_BLOCK_SIZE	1024
 ENUM_VALUE_LIST	NULL
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
-VARIABLE_NAME	RAND_SEED1
-SESSION_VALUE	0
-GLOBAL_VALUE	NULL
-GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	0
-VARIABLE_SCOPE	SESSION ONLY
-VARIABLE_TYPE	BIGINT UNSIGNED
-VARIABLE_COMMENT	Sets the internal state of the RAND() generator for replication purposes
-NUMERIC_MIN_VALUE	0
-NUMERIC_MAX_VALUE	18446744073709551615
-NUMERIC_BLOCK_SIZE	1
-ENUM_VALUE_LIST	NULL
-READ_ONLY	NO
-COMMAND_LINE_ARGUMENT	NULL
-VARIABLE_NAME	RAND_SEED2
-SESSION_VALUE	0
-GLOBAL_VALUE	NULL
-GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	0
-VARIABLE_SCOPE	SESSION ONLY
-VARIABLE_TYPE	BIGINT UNSIGNED
-VARIABLE_COMMENT	Sets the internal state of the RAND() generator for replication purposes
-NUMERIC_MIN_VALUE	0
-NUMERIC_MAX_VALUE	18446744073709551615
-NUMERIC_BLOCK_SIZE	1
-ENUM_VALUE_LIST	NULL
-READ_ONLY	NO
-COMMAND_LINE_ARGUMENT	NULL
 VARIABLE_NAME	RANGE_ALLOC_BLOCK_SIZE
 SESSION_VALUE	4096
 GLOBAL_VALUE	4096
@@ -4051,6 +4025,8 @@ where variable_name in (
 'lower_case_file_system',
 'lower_case_table_names',
 'open_files_limit',
+'rand_seed1',
+'rand_seed2',
 'system_time_zone',
 'version_comment',
 'version_compile_machine', 'version_compile_os',
@@ -4127,6 +4103,26 @@ NUMERIC_BLOCK_SIZE	1
 ENUM_VALUE_LIST	NULL
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	RAND_SEED1
+VARIABLE_SCOPE	SESSION ONLY
+VARIABLE_TYPE	BIGINT UNSIGNED
+VARIABLE_COMMENT	Sets the internal state of the RAND() generator for replication purposes
+NUMERIC_MIN_VALUE	0
+NUMERIC_MAX_VALUE	18446744073709551615
+NUMERIC_BLOCK_SIZE	1
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	NULL
+VARIABLE_NAME	RAND_SEED2
+VARIABLE_SCOPE	SESSION ONLY
+VARIABLE_TYPE	BIGINT UNSIGNED
+VARIABLE_COMMENT	Sets the internal state of the RAND() generator for replication purposes
+NUMERIC_MIN_VALUE	0
+NUMERIC_MAX_VALUE	18446744073709551615
+NUMERIC_BLOCK_SIZE	1
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	NULL
 VARIABLE_NAME	SYSTEM_TIME_ZONE
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	VARCHAR

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -15,6 +15,8 @@ variable_name not in (
 'lower_case_file_system',
 'lower_case_table_names',
 'open_files_limit',
+'rand_seed1',
+'rand_seed2',
 'system_time_zone',
 'version_comment',
 'version_compile_machine', 'version_compile_os',
@@ -3269,34 +3271,6 @@ NUMERIC_BLOCK_SIZE	1024
 ENUM_VALUE_LIST	NULL
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
-VARIABLE_NAME	RAND_SEED1
-SESSION_VALUE	0
-GLOBAL_VALUE	NULL
-GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	0
-VARIABLE_SCOPE	SESSION ONLY
-VARIABLE_TYPE	BIGINT UNSIGNED
-VARIABLE_COMMENT	Sets the internal state of the RAND() generator for replication purposes
-NUMERIC_MIN_VALUE	0
-NUMERIC_MAX_VALUE	18446744073709551615
-NUMERIC_BLOCK_SIZE	1
-ENUM_VALUE_LIST	NULL
-READ_ONLY	NO
-COMMAND_LINE_ARGUMENT	NULL
-VARIABLE_NAME	RAND_SEED2
-SESSION_VALUE	0
-GLOBAL_VALUE	NULL
-GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	0
-VARIABLE_SCOPE	SESSION ONLY
-VARIABLE_TYPE	BIGINT UNSIGNED
-VARIABLE_COMMENT	Sets the internal state of the RAND() generator for replication purposes
-NUMERIC_MIN_VALUE	0
-NUMERIC_MAX_VALUE	18446744073709551615
-NUMERIC_BLOCK_SIZE	1
-ENUM_VALUE_LIST	NULL
-READ_ONLY	NO
-COMMAND_LINE_ARGUMENT	NULL
 VARIABLE_NAME	RANGE_ALLOC_BLOCK_SIZE
 SESSION_VALUE	4096
 GLOBAL_VALUE	4096
@@ -4793,6 +4767,8 @@ where variable_name in (
 'lower_case_file_system',
 'lower_case_table_names',
 'open_files_limit',
+'rand_seed1',
+'rand_seed2',
 'system_time_zone',
 'version_comment',
 'version_compile_machine', 'version_compile_os',
@@ -4869,6 +4845,26 @@ NUMERIC_BLOCK_SIZE	1
 ENUM_VALUE_LIST	NULL
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	RAND_SEED1
+VARIABLE_SCOPE	SESSION ONLY
+VARIABLE_TYPE	BIGINT UNSIGNED
+VARIABLE_COMMENT	Sets the internal state of the RAND() generator for replication purposes
+NUMERIC_MIN_VALUE	0
+NUMERIC_MAX_VALUE	18446744073709551615
+NUMERIC_BLOCK_SIZE	1
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	NULL
+VARIABLE_NAME	RAND_SEED2
+VARIABLE_SCOPE	SESSION ONLY
+VARIABLE_TYPE	BIGINT UNSIGNED
+VARIABLE_COMMENT	Sets the internal state of the RAND() generator for replication purposes
+NUMERIC_MIN_VALUE	0
+NUMERIC_MAX_VALUE	18446744073709551615
+NUMERIC_BLOCK_SIZE	1
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	NULL
 VARIABLE_NAME	SYSTEM_TIME_ZONE
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	VARCHAR

mysql-test/suite/sys_vars/t/rand_seed1_basic.test

@@ -6,6 +6,9 @@
 #
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 select @@global.rand_seed1;
+--error ER_NO_DEFAULT
+set session rand_seed1=default;
+set session rand_seed1=10969771;
 select @@session.rand_seed1;
 show global variables like 'rand_seed1';
 show session variables like 'rand_seed1';

mysql-test/suite/sys_vars/t/rand_seed2_basic.test

@@ -7,6 +7,9 @@
 #
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 select @@global.rand_seed2;
+--error ER_NO_DEFAULT
+set session rand_seed2=default;
+set session rand_seed2=10969771;
 select @@session.rand_seed2;
 show global variables like 'rand_seed2';
 show session variables like 'rand_seed2';

mysql-test/t/set_statement.test

@@ -1050,10 +1050,6 @@ set statement autocommit=default for select 1;
 --error ER_SET_STATEMENT_NOT_SUPPORTED
 set statement tx_isolation=default for select 1;
 --error ER_SET_STATEMENT_NOT_SUPPORTED
-set statement rand_seed1=default for select 1;
---error ER_SET_STATEMENT_NOT_SUPPORTED
-set statement rand_seed2=default for select 1;
---error ER_SET_STATEMENT_NOT_SUPPORTED
 set statement skip_replication=default for select 1;
 --error ER_SET_STATEMENT_NOT_SUPPORTED
 set statement sql_log_off=default for select 1;
@@ -1115,3 +1111,23 @@ set @@old_passwords=@save_old_passwords;
 --error ER_UNKNOWN_SYSTEM_VARIABLE
 set statement non_existing=1 for select 1;
 show errors;
+
+--echo #
+--echo # MDEV-6954: SET STATEMENT rand_seedX = ...FOR ... makes
+--echo # the next rand() to return 0
+--echo #
+set @rnd=1;
+let $1=10;
+--disable_query_log
+--echo # test that rand() is not always 0 after restoring rand_seed, rand_seed2...
+while ($1)
+{
+  --disable_result_log
+  set statement rand_seed1=1, rand_seed2=1 for select 1;
+  --enable_result_log
+  set @rnd= rand()=0 and @rnd;
+  dec $1;
+}
+--enable_query_log
+--echo # @rnd should be 0
+select @rnd;

sql/sys_vars.cc

@@ -3830,17 +3830,17 @@ static bool update_rand_seed1(THD *thd, set_var *var)
   thd->rand.seed1= (ulong) var->save_result.ulonglong_value;
   return false;
 }
-static ulonglong read_rand_seed(THD *thd)
+static ulonglong read_rand_seed1(THD *thd)
 {
-  return 0;
+  return thd->rand.seed1;
 }
 static Sys_var_session_special Sys_rand_seed1(
        "rand_seed1", "Sets the internal state of the RAND() "
        "generator for replication purposes",
-       NO_SET_STMT sys_var::ONLY_SESSION, NO_CMD_LINE,
+       sys_var::ONLY_SESSION, NO_CMD_LINE,
        VALID_RANGE(0, ULONG_MAX), BLOCK_SIZE(1),
        NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
-       ON_UPDATE(update_rand_seed1), ON_READ(read_rand_seed));
+       ON_UPDATE(update_rand_seed1), ON_READ(read_rand_seed1));
 
 static bool update_rand_seed2(THD *thd, set_var *var)
 {
@@ -3852,13 +3852,17 @@ static bool update_rand_seed2(THD *thd, set_var *var)
   thd->rand.seed2= (ulong) var->save_result.ulonglong_value;
   return false;
 }
+static ulonglong read_rand_seed2(THD *thd)
+{
+  return thd->rand.seed2;
+}
 static Sys_var_session_special Sys_rand_seed2(
        "rand_seed2", "Sets the internal state of the RAND() "
        "generator for replication purposes",
-       NO_SET_STMT sys_var::ONLY_SESSION, NO_CMD_LINE,
+       sys_var::ONLY_SESSION, NO_CMD_LINE,
        VALID_RANGE(0, ULONG_MAX), BLOCK_SIZE(1),
        NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
-       ON_UPDATE(update_rand_seed2), ON_READ(read_rand_seed));
+       ON_UPDATE(update_rand_seed2), ON_READ(read_rand_seed2));
 
 static ulonglong read_error_count(THD *thd)
 {