当 MySQL 中的记录为 NULL 时，在新列中返回 0?
mysqlmysqli database更新于 2023/10/23 6:26:00
为此，您可以使用 CASE 语句。让我们首先创建一个表 −
mysql> create table DemoTable703 (Price int); Query OK, 0 rows affected (0.46 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable703 values(102); Query OK, 1 row affected (0.27 sec) mysql> insert into DemoTable703 values(null); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable703 values(0); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable703 values(500); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable703 values(100); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable703 values(null); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable703 values(2340); Query OK, 1 row affected (0.14 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable703;
这将产生以下输出 -
+-------+ | Price | +-------+ | 102 | | NULL | | 0 | | 500 | | 100 | | NULL | | 2340 | +-------+ 7 rows in set (0.00 sec)
使用 CASE 语句 −
mysql> select Price, case When Price IS NULL Then 0 else Price END AS Result from DemoTable703;
这将产生以下输出 -
+-------+--------+ | Price | Result | +-------+--------+ | 102 | 102 | | NULL | 0 | | 0 | 0 | | 500 | 500 | | 100 | 100 | | NULL | 0 | | 2340 | 2340 | +-------+--------+ 7 rows in set (0.00 sec)
