/ Check-in [1d4c92c7]
Login

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Update the NULL-handling document to show current behavior of OCELOT. (CVS 1046)
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1:1d4c92c7325f69ee84b901a2de74a306ace134b6
User & Date: drh 2003-07-07 00:10:40
Context
2003-07-07
10:47
A proported fix for ticket #374. (CVS 1047) check-in: a49ee69e user: drh tags: trunk
00:10
Update the NULL-handling document to show current behavior of OCELOT. (CVS 1046) check-in: 1d4c92c7 user: drh tags: trunk
2003-07-06
17:22
Correctly handle comparing an INTEGER PRIMARY KEY against a floating point number. Ticket #377. (CVS 1045) check-in: 982aa335 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to www/nulls.tcl.

1
2
3
4
5
6
7
8
9
10
11
..
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
..
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69

70
71
72
73
74
75
76
77
78

79
80
81
82
83
84
85
86

87
88
89
90
91
92
93
94

95
96

97
98
99
100
101
102
103
...
104
105
106
107
108
109
110

111
112
113
114
115
116
117
118

119
120

121
122
123
124
125
126
127
...
128
129
130
131
132
133
134

135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
#
# Run this script to generated a nulls.html output file
#
set rcsid {$Id: nulls.tcl,v 1.2 2003/07/01 01:16:30 drh Exp $}

puts {<html>
<head>
<title>NULL Handling In SQLite Versus Other Database Engines</title>
</head>
<body bgcolor="white">
<h1 align="center">
................................................................................
SQLite was originally coded in such a way that the answer to
all questions in the chart below would be "Yes".  But the
expriments run on other SQL engines showed that none of them
worked this way.  So SQLite was modified to work the same as
Oracle, PostgreSQL, and DB2.  This involved making NULLs
indistinct for the purposes of the SELECT DISTINCT statement and
for the UNION operator in a SELECT.  NULLs are still distinct
in a UNIQUE index.  This seems somewhat arbitrary, but the desire
to be compatible with other engines outweighted that objection.
</p>

<p>
It is possible to make SQLite treat NULLs as distinct for the
purposes of the SELECT DISTINCT and UNION.  To do so, one should
change the value of the NULL_ALWAYS_DISTINCT #define in the
................................................................................
<tt>sqliteInt.h</tt> source file and recompile.
</p>

<p>
The following table shows the results of the NULL handling experiments.
</p>

<table border=1 cellpadding=5 width="100%">
<tr><th>&nbsp&nbsp;</th>
<th>SQLite</th>
<th>PostgreSQL</th>
<th>Oracle</th>
<th>Informix</th>
<th>DB2</th>
<th>MS-SQL</th>

</tr>

<tr><td>Adding anything to null gives null</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>

</tr>
<tr><td>Multiplying null by zero gives null</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>

</tr>
<tr><td>nulls are distinct in a UNIQUE index</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>

</tr>
<tr><td>nulls are distinct in SELECT DISTINCT</td>

<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
</tr>
................................................................................
<tr><td>nulls are distinct in a UNION</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>

</tr>
<tr><td>"CASE WHEN null THEN 1 ELSE 0 END" is 0?</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>

</tr>
<tr><td>"null OR true" is true</td>

<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
................................................................................
<tr><td>"not (null AND false)" is true</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>

</tr>
</table>

<table border=1 cellpadding=5 width="100%">
<tr><th>&nbsp&nbsp;</th>
<th>MySQL</th>
<th>OCELOT</th>
<th>Firebird</th>
<th>SQL Anywhere</th>
<th>Borland Interbase</th>
</tr>

<tr><td>Adding anything to null gives null</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>Multiplying null by zero gives null</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>nulls are distinct in a UNIQUE index</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 4)</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 4)</td>
</tr>
<tr><td>nulls are distinct in SELECT DISTINCT</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 1)</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
</tr>
<tr><td>nulls are distinct in a UNION</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 3)</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 1)</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
</tr>
<tr><td>"CASE WHEN null THEN 1 ELSE 0 END" is 0?</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 2)</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 5)</td>
</tr>
<tr><td>"null OR true" is true</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>"not (null AND false)" is true</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
</table>




|







 







|







 







|







>









>








>

|






>


>







 







>








>


>







 







>



|


<






<










<

|
<







<






<





<







<





<







1
2
3
4
5
6
7
8
9
10
11
..
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
..
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
...
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
...
136
137
138
139
140
141
142
143
144
145
146
147
148
149

150
151
152
153
154
155

156
157
158
159
160
161
162
163
164
165

166
167

168
169
170
171
172
173
174

175
176
177
178
179
180

181
182
183
184
185

186
187
188
189
190
191
192

193
194
195
196
197

198
199
200
201
202
203
204
#
# Run this script to generated a nulls.html output file
#
set rcsid {$Id: nulls.tcl,v 1.3 2003/07/07 00:10:40 drh Exp $}

puts {<html>
<head>
<title>NULL Handling In SQLite Versus Other Database Engines</title>
</head>
<body bgcolor="white">
<h1 align="center">
................................................................................
SQLite was originally coded in such a way that the answer to
all questions in the chart below would be "Yes".  But the
expriments run on other SQL engines showed that none of them
worked this way.  So SQLite was modified to work the same as
Oracle, PostgreSQL, and DB2.  This involved making NULLs
indistinct for the purposes of the SELECT DISTINCT statement and
for the UNION operator in a SELECT.  NULLs are still distinct
in a UNIQUE column.  This seems somewhat arbitrary, but the desire
to be compatible with other engines outweighted that objection.
</p>

<p>
It is possible to make SQLite treat NULLs as distinct for the
purposes of the SELECT DISTINCT and UNION.  To do so, one should
change the value of the NULL_ALWAYS_DISTINCT #define in the
................................................................................
<tt>sqliteInt.h</tt> source file and recompile.
</p>

<p>
The following table shows the results of the NULL handling experiments.
</p>

<table border=1 cellpadding=3 width="100%">
<tr><th>&nbsp&nbsp;</th>
<th>SQLite</th>
<th>PostgreSQL</th>
<th>Oracle</th>
<th>Informix</th>
<th>DB2</th>
<th>MS-SQL</th>
<th>OCELOT</th>
</tr>

<tr><td>Adding anything to null gives null</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>Multiplying null by zero gives null</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>nulls are distinct in a UNIQUE column</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>nulls are distinct in SELECT DISTINCT</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
</tr>
................................................................................
<tr><td>nulls are distinct in a UNION</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
</tr>
<tr><td>"CASE WHEN null THEN 1 ELSE 0 END" is 0?</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>"null OR true" is true</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
................................................................................
<tr><td>"not (null AND false)" is true</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
</table>

<table border=1 cellpadding=3 width="100%">
<tr><th>&nbsp&nbsp;</th>
<th>MySQL</th>

<th>Firebird</th>
<th>SQL Anywhere</th>
<th>Borland Interbase</th>
</tr>

<tr><td>Adding anything to null gives null</td>

<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>Multiplying null by zero gives null</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>

</tr>
<tr><td>nulls are distinct in a UNIQUE column</td>

<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 4)</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 4)</td>
</tr>
<tr><td>nulls are distinct in SELECT DISTINCT</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>

<td valign="center" align="center" bgcolor="#aaaad2">(Note 1)</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
</tr>
<tr><td>nulls are distinct in a UNION</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 3)</td>

<td valign="center" align="center" bgcolor="#aaaad2">(Note 1)</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
</tr>
<tr><td>"CASE WHEN null THEN 1 ELSE 0 END" is 0?</td>

<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 2)</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#aaaad2">(Note 5)</td>
</tr>
<tr><td>"null OR true" is true</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>

<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
<tr><td>"not (null AND false)" is true</td>

<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
</tr>
</table>