可以改为: ```sql ALTER TABLE t ALTER COLUMN num SET DEFAULT 0; SELECT id FROM t WHERE num = 0; ``` 3. **谨慎使用!= 或 **:这些符号会导致索引失效,从而触发全表扫描。应尽量避免使用。 4. **限制...
一瓢一瓢的饮 alanchanchn的博客 +----------------------+ | current catalog name | +----------------------+ | default_catalog | +----------------------+ 1 row in set Flink SQL> create database IF NOT EXISTS default_catalog.alan_test...
- 使用EXISTS替代IN,例如,`SELECT * FROM table WHERE id EXISTS (SELECT 1 FROM other_table WHERE table.id = other_table.id)` 比 `SELECT * FROM table WHERE id IN (SELECT id FROM other_table)` 更高效。...
十吾十吾的博客mysql建立数据库报错You have an error in your SQL syntax; check the manual that corresponds to your MySQL se在使用xshell远程连接我的服务器时想创建一个数据库结果执行不对,sql语句如下mysql> create ...