Description:
GROUP_CONCAT is prone to frequent silent truncation because the default max length is 1024 characters. Increasing this default would lessen the likelihood of truncation, but this is not necessarily an improvement, since the situation can still occur.
How to repeat:
CREATE TABLE t1 (id int not null primary key auto_increment, b int not null);
INSERT INTO t1 VALUES (NULL, 1);
INSERT INTO t1 select null, 1 from t1;
INSERT INTO t1 select null, 1 from t1 a, t1 b, t1 c;
INSERT INTO t1 select null, 1 from t1 a, t1 b, t1 c;
INSERT INTO t1 select null, 2 from t1;
select group_concat(id) from t1 group by b\G
*************************** 1. row ***************************
group_concat(id): 1,2,3,4,5,6,7,8,9,10,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,2
*************************** 2. row ***************************
group_concat(id): 1041,1042,1043,1044,1045,1046,1047,1048,1049,1050,1051,1052,1053,1054,1055,1056,1057,1058,1059,1060,1061,1062,1063,1064,1065,1066,1067,1068,1069,1070,1071,1072,1073,1074,1075,1076,1077,1078,1079,1080,1081,1082,1083,1084,1085,1086,1087,1088,1089,1090,1091,1092,1093,1094,1095,1096,1097,1098,1099,1100,1101,1102,1103,1104,1105,1106,1107,1108,1109,1110,1111,1112,1113,1114,1115,1116,1117,1118,1119,1120,1121,1122,1123,1124,1125,1126,1127,1128,1129,1130,1131,1132,1133,1134,1135,1136,1137,1138,1139,1140,1141,1142,1143,1144,1145,1146,1147,1148,1149,1150,1151,1152,1153,1154,1155,1156,1157,1158,1159,1160,1161,1162,1163,1164,1165,1166,1167,1168,1169,1170,1171,1172,1173,1174,1175,1176,1177,1178,1179,1180,1181,1182,1183,1184,1185,1186,1187,1188,1189,1190,1191,1192,1193,1194,1195,1196,1197,1198,1199,1200,1201,1202,1203,1204,1205,1206,1207,1208,1209,1210,1211,1212,1213,1214,1215,1216,1217,1218,1219,1220,1221,1222,1223,1224,1225,1226,1227,1228,1229,1230,1231,1232,1233,1234,1235,1236,1237,1238,1239,1240,1241,1242,1243,1244,1245
2 rows in set, 2 warnings (0.01 sec)
mysql [localhost] {msandbox} (test) > show warnings;
+---------+------+-----------------------------------+
| Level | Code | Message |
+---------+------+-----------------------------------+
| Warning | 1260 | Row 282 was cut by GROUP_CONCAT() |
| Warning | 1260 | Row 488 was cut by GROUP_CONCAT() |
+---------+------+-----------------------------------+
2 rows in set (0.00 sec)
mysql [localhost] {msandbox} (test) > select @@sql_mode\G
*************************** 1. row ***************************
@@sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
Suggested fix:
Convert the warnings to be errors when a strict mode is enabled.
Description: GROUP_CONCAT is prone to frequent silent truncation because the default max length is 1024 characters. Increasing this default would lessen the likelihood of truncation, but this is not necessarily an improvement, since the situation can still occur. How to repeat: CREATE TABLE t1 (id int not null primary key auto_increment, b int not null); INSERT INTO t1 VALUES (NULL, 1); INSERT INTO t1 select null, 1 from t1; INSERT INTO t1 select null, 1 from t1 a, t1 b, t1 c; INSERT INTO t1 select null, 1 from t1 a, t1 b, t1 c; INSERT INTO t1 select null, 2 from t1; select group_concat(id) from t1 group by b\G *************************** 1. row *************************** group_concat(id): 1,2,3,4,5,6,7,8,9,10,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,2 *************************** 2. row *************************** group_concat(id): 1041,1042,1043,1044,1045,1046,1047,1048,1049,1050,1051,1052,1053,1054,1055,1056,1057,1058,1059,1060,1061,1062,1063,1064,1065,1066,1067,1068,1069,1070,1071,1072,1073,1074,1075,1076,1077,1078,1079,1080,1081,1082,1083,1084,1085,1086,1087,1088,1089,1090,1091,1092,1093,1094,1095,1096,1097,1098,1099,1100,1101,1102,1103,1104,1105,1106,1107,1108,1109,1110,1111,1112,1113,1114,1115,1116,1117,1118,1119,1120,1121,1122,1123,1124,1125,1126,1127,1128,1129,1130,1131,1132,1133,1134,1135,1136,1137,1138,1139,1140,1141,1142,1143,1144,1145,1146,1147,1148,1149,1150,1151,1152,1153,1154,1155,1156,1157,1158,1159,1160,1161,1162,1163,1164,1165,1166,1167,1168,1169,1170,1171,1172,1173,1174,1175,1176,1177,1178,1179,1180,1181,1182,1183,1184,1185,1186,1187,1188,1189,1190,1191,1192,1193,1194,1195,1196,1197,1198,1199,1200,1201,1202,1203,1204,1205,1206,1207,1208,1209,1210,1211,1212,1213,1214,1215,1216,1217,1218,1219,1220,1221,1222,1223,1224,1225,1226,1227,1228,1229,1230,1231,1232,1233,1234,1235,1236,1237,1238,1239,1240,1241,1242,1243,1244,1245 2 rows in set, 2 warnings (0.01 sec) mysql [localhost] {msandbox} (test) > show warnings; +---------+------+-----------------------------------+ | Level | Code | Message | +---------+------+-----------------------------------+ | Warning | 1260 | Row 282 was cut by GROUP_CONCAT() | | Warning | 1260 | Row 488 was cut by GROUP_CONCAT() | +---------+------+-----------------------------------+ 2 rows in set (0.00 sec) mysql [localhost] {msandbox} (test) > select @@sql_mode\G *************************** 1. row *************************** @@sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION Suggested fix: Convert the warnings to be errors when a strict mode is enabled.