SELECT * FROM your_table FETCH FIRST 10 ROWS ONLY;
, **说明**:这是DB2中最常用的方法之一,用于限制查询结果的行数。其语法简单直观,常用于分页查询和限制结果集。,,2. **使用ROW_NUMBER()函数**, **语法**:`SELECT * FROM (SELECT your_columns, ROW_NUMBER() OVER (ORDER BY your_sort_column) AS row_num FROM your_table) AS subquery WHERE row_numSELECT
语句结合 GROUP BY
和 HAVING
子句来查询重复数据。Db
类来实现。,,``php,$db = M('table_name'); // 实例化模型,$data = $db>where('column_name=1')>select(); // 执行查询,
``GROUP BY
和HAVING
子句。假设你有一个名为users
的表,并且你想查找在email
列中重复的记录,你可以使用以下查询:,,``sql,SELECT email, COUNT(*),FROM users,GROUP BY email,HAVING COUNT(*) > 1;,
`,,这个查询会返回所有在
email`列中出现超过一次的记录及其出现的次数。sql,SELECT table_name AS "Table", pg_size_pretty(pg_total_relation_size(table_name::cstring)) AS "Size" FROM information_schema.tables;,
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