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【mysql】UPDATEで連番を振り直す

はじめに

  • テストとかしてカラムごにゃった時に番号がずれてしまったりしたので、連番をきれいに振り直したいと思ったしだい。
  • 忘れがちなので、書いておくことにした

mysql のバージョン

mysql> select version();
+-----------+
| version() |
+-----------+
| 5.7.28    |
+-----------+

やってみる

  • 例えば、この↓ select文のnoが1から始まって欲しいのに2から始まってる。
mysql> select id, no from tests; 
+----+----+
| id | no |
+----+----+
|  1 |  2 |
|  2 |  3 |
|  3 |  4 |
|  4 |  5 |
+----+----+
4 rows in set (0.00 sec)
  • 振り直す!!
mysql> set @cnt_i:=0; update tests set no = (@cnt_i := @cnt_i + 1 );

Query OK, 0 rows affected (0.00 sec)
Query OK, 4 rows affected (0.00 sec)
Rows matched: 4  Changed: 4  Warnings: 0
  • 確認してみる。無事に no が 1 からの連番になっている。やったー
mysql> select id, no from tests; 
+----+----+
| id | no |
+----+----+
|  1 |  1 |
|  2 |  2 |
|  3 |  3 |
|  4 |  4 |
+----+----+
4 rows in set (0.01 sec)
MochiMochiChip
2020年は初心にかえります。ただいま
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