Fix sorting of NULL values (Should always be first) (9d9bcf25) · Commits · Software / OSDI20 Artifacts / mariadb

Docs/manual.texi

+31 −5

Original line number	Diff line number	Diff line
		@@ -8146,6 +8146,9 @@ version 4.0;

		@itemize @bullet
		@item
		Use @code{ORDER BY column DESC} now always sorts @code{NULL} values
		first; In 3.23 this was not always consistent.
		@item
		@code{SHOW INDEX} has 2 columns more (@code{Null} and @code{Index_type})
		than it had in 3.23.
		@item
		@@ -12661,9 +12664,15 @@ mysql> SELECT 1 IS NULL, 1 IS NOT NULL;
		+-----------+---------------+
		@end example

		Note that two @code{NULL} are compared as equal is when you do an
		@code{GROUP BY}.

		In MySQL, 0 or @code{NULL} means false and anything else means true.
		The default truth value from a boolean operation is 1.

		When doing an @code{ORDER BY}, @code{NULL} values are always sorted first,
		even if you are using @code{DESC}.

		This special treatment of @code{NULL} is why, in the previous section, it
		was necessary to determine which animals are no longer alive using
		@code{death IS NOT NULL} instead of @code{death <> NULL}.
		@@ -13191,7 +13200,7 @@ mysql> DESCRIBE pet;
		@end example

		@code{Field} indicates the column name, @code{Type} is the data type for
		the column, @code{Null} indicates whether or not the column can contain
		the column, @code{NULL} indicates whether or not the column can contain
		@code{NULL} values, @code{Key} indicates whether or not the column is
		indexed, and @code{Default} specifies the column's default value.

		@@ -16481,8 +16490,10 @@ password will be set to the password specified by the @code{IDENTIFIED BY}
		clause, if one is given. If the user already had a password, it is replaced
		by the new one.

		Optional @code{PASSWORD} changes behaviour of @code{IDENTIFIED BY} from
		accepting plain password to accept encrypted password as argument.
		If you don't want to send the password in clear text you can use the
		@code{PASSWORD} option followed by a scrambled password from SQL
		function @code{PASSWORD()} or the C API function
		@code{make_scrambled_password(char to, const char password)}.

		@strong{Warning:} If you create a new user but do not specify an
		@code{IDENTIFIED BY} clause, the user has no password. This is insecure.
		@@ -25531,7 +25542,13 @@ You have different @code{ORDER BY} and @code{GROUP BY} expressions.

		@item
		The used table index is an index type that doesn't store rows in order.
		(Like index in @code{HEAP} tables).
		(Like the @code{HASH} index in @code{HEAP} tables).

		@item
		The index colum may contain @code{NULL} values and one is using
		@code{ORDER BY ... DESC}. This is because in SQL @code{NULL} values is
		always sorted before normal values, independent of you are using
		@code{DESC} or not.
		@end itemize


		@@ -26466,6 +26483,9 @@ probably much faster, as this will require us to do much fewer seeks.)
		Note that if such a query uses @code{LIMIT} to only retrieve
		part of the rows, MySQL will use an index anyway, as it can
		much more quickly find the few rows to return in the result.
		@item
		If the index range may contain @code{NULL} values and you are using
		@code{ORDER BY ... DESC}
		@end itemize

		@node Indexes, Multiple-column indexes, MySQL indexes, Optimising Database Structure
		@@ -29975,7 +29995,7 @@ mysql> select 2 > 2;
		@cindex @code{NULL}, testing for null
		@findex <=> (Equal to)
		@item <=>
		Null safe equal:
		NULL safe equal:
		@example
		mysql> select 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
		-> 1 1 0
		@@ -48618,6 +48638,12 @@ Our TODO section contains what we plan to have in 4.0. @xref{TODO MySQL 4.0}.

		@itemize @bullet
		@item
		Use @code{ORDER BY column DESC} now sorts @code{NULL} values first.
		@item
		Fixed bug in @code{SELECT DISTINCT ... ORDER BY DESC} optimization.
		@item
		Fixed bug in @code{... HAVING 'GROUP_FUNCTION'(xxx) IS [NOT] NULL}.
		@item
		Allow numeric user id to @code{mysqld --user=#}.
		@item
		Fixed a bug where @code{SQL_CALC_ROWS} returned a wrong value when used

client/mysqldump.c

+8 −7

Original line number	Diff line number	Diff line
		@@ -35,7 +35,7 @@
		** and adapted to mysqldump 05/11/01 by Jani Tolonen
		*/

		#define DUMP_VERSION "8.22"
		#define DUMP_VERSION "8.23"

		#include <my_global.h>
		#include <my_sys.h>
		@@ -897,8 +897,6 @@ static uint getTableStructure(char table, char db)
		fputs(";\n", sql_file);
		}
		}
		if (opt_disable_keys)
		fprintf(sql_file,"\n/!40000 ALTER TABLE %s DISABLE KEYS /;\n",table_name);
		if (cFlag)
		{
		strpos=strmov(strpos,") VALUES ");
		@@ -1023,7 +1021,7 @@ static void dumpTable(uint numFields, char *table)
		strxmov(strend(query), " WHERE ",where,NullS);
		}
		if (!opt_xml)
		fputs("\n\n", md_result_file);
		fputs("\n", md_result_file);
		if (mysql_query(sock, query))
		{
		DBerror(sock, "when retrieving data from server");
		@@ -1048,6 +1046,9 @@ static void dumpTable(uint numFields, char *table)
		return;
		}

		if (opt_disable_keys)
		fprintf(md_result_file,"/!40000 ALTER TABLE %s DISABLE KEYS /;\n",
		quote_name(table, table_buff));
		if (opt_lock)
		fprintf(md_result_file,"LOCK TABLES %s WRITE;\n",
		quote_name(table,table_buff));
		@@ -1207,11 +1208,11 @@ static void dumpTable(uint numFields, char *table)
		safe_exit(EX_CONSCHECK);
		return;
		}
		if (opt_disable_keys)
		fprintf(md_result_file,"\n/!40000 ALTER TABLE %s ENABLE KEYS /;\n",
		quote_name(table,table_buff));
		if (opt_lock)
		fputs("UNLOCK TABLES;\n", md_result_file);
		if (opt_disable_keys)
		fprintf(md_result_file,"/!40000 ALTER TABLE %s ENABLE KEYS /;\n",
		quote_name(table,table_buff));
		if (opt_autocommit)
		fprintf(md_result_file, "commit;\n");
		mysql_free_result(res);

mysql-test/r/distinct.result

+14 −1

Original line number	Diff line number	Diff line
		@@ -77,6 +77,7 @@ NULL NULL
		10 VMT
		select id+0 as a,max(id),concat(facility) as b from t1 group by a order by b desc,a;
		a max(id) b
		NULL NULL NULL
		10 10 VMT
		9 9 SRV
		8 8 RV
		@@ -89,7 +90,6 @@ a max(id) b
		1 1 /L
		-1 -1
		0 0
		NULL NULL NULL
		select id >= 0 and id <= 5 as grp,count(*) from t1 group by grp;
		grp count(*)
		0 7
		@@ -336,3 +336,16 @@ a c
		4 NULL
		3 NULL
		drop table t1;
		create table t1 (a char(1), key(a)) type=myisam;
		insert into t1 values('1'),('1');
		select * from t1 where a >= '1';
		a
		1
		1
		select distinct a from t1 order by a desc;
		a
		1
		select distinct a from t1 where a >= '1' order by a desc;
		a
		1
		drop table t1;

mysql-test/r/group_by.result

+3 −1

Original line number	Diff line number	Diff line
		@@ -226,7 +226,7 @@ key (score)
		INSERT INTO t1 VALUES (1,1,1),(2,2,2),(2,1,1),(3,3,3),(4,3,3),(5,3,3);
		explain select userid,count(*) from t1 group by userid desc;
		table type possible_keys key key_len ref rows Extra
		t1 ALL NULL NULL NULL NULL 6 Using temporary
		t1 ALL NULL NULL NULL NULL 6 Using temporary; Using filesort
		select userid,count(*) from t1 group by userid desc;
		userid count(*)
		3 3
		@@ -244,6 +244,8 @@ spid count(*)
		2 2
		select spid,count(*) from t1 where spid between 1 and 2 group by spid desc;
		spid count(*)
		2 2
		1 1
		explain select sql_big_result spid,sum(userid) from t1 group by spid desc;
		table type possible_keys key key_len ref rows Extra
		t1 ALL NULL NULL NULL NULL 6 Using filesort

mysql-test/r/having.result

+19 −0

Original line number	Diff line number	Diff line
		@@ -44,3 +44,22 @@ AND start <= 999660;
		id start end chr_strand
		133197 813898 813898 -1.0000
		drop table t1,t2;
		CREATE TABLE t1 (Fld1 int(11) default NULL,Fld2 int(11) default NULL);
		INSERT INTO t1 VALUES (1,10),(1,20),(2,NULL),(2,NULL),(3,50);
		select Fld1, max(Fld2) as q from t1 group by Fld1 having q is not null;
		Fld1 q
		1 20
		3 50
		select Fld1, max(Fld2) from t1 group by Fld1 having max(Fld2) is not null;
		Fld1 max(Fld2)
		1 20
		3 50
		select Fld1, max(Fld2) from t1 group by Fld1 having avg(Fld2) is not null;
		Fld1 max(Fld2)
		1 20
		3 50
		select Fld1, max(Fld2) from t1 group by Fld1 having std(Fld2) is not null;
		Fld1 max(Fld2)
		1 20
		3 50
		drop table t1;