参考:https://deepinout.com/sql/sql-questions/124_sql_if_exists_before_insert_update_delete_for_optimization.html DROPTABLEIFEXISTSauthor; 参考2:http://www.manongjc.com/detail/31-wcvyoxykttgzfpj.html 标签:SQL,PostgreSQL 好文要顶关注我收藏该文微信分享 ...
下面的示例取决于 INSERT 和 DELETE 语句的成功操作。局部变量在两条语句后均被设置为 @@ERROR 的值,并且用于此操作的共享错误处理例程中。 USE pubs GO DECLARE @del_error int, @ins_error int -- Start a transaction. BEGIN TRAN -- Execute the DELETE statement. DELETE authors WHERE au_id = '409-...
USEAdventureWorks2022; GO-- determines if function exists in databaseIF OBJECT_ID (N'Sales.fn_SalesByStore', N'IF') IS NOT NULL-- deletes functionDROPFUNCTIONSales.fn_SalesByStore; GO 另请参阅 DROP FUNCTION (Transact-SQL) 反馈 此页面是否有帮助?
WHERE some_column=some_value; (8)DELETE 语句 用于删除表中的记录 DELETE FROM table_name WHERE some_column=some_value; 3、SQL进阶语法 (1)SELECT TOP, LIMIT, ROWNUM 子句 用于规定要返回的记录的数目。 SQL Server / MS Access 语法 SELECT TOP number|percent column_name(s) FROM table_name; MySQL...
DROP TABLE IF EXISTS student;删除被其他表外键引用的表格时，需先解除关联或删除依赖表。生产环境操作前建议备份数据。删除表内数据 若仅需清空表格数据但保留结构，使用TRUNCATETABLE或DELETE语句。1. TRUNCATE TABLE 快速清空表格数据，不可回滚，适用于大数据量场景。语法：TRUNCATE TABLE表名;示例：清空student表数据...
问错误: SQL命令中不存在列“exist”EN我试图了解一下触发器，我想做一个触发器，检查我是否在我的...
What about the performance difference in doing a delete and insert vs. an update? I have an application that will probably always update 4 rows in the table (after the first iteration). Performance wise, should I do a delete for those four rows and then insert each row or simply do four...
If you are thinking of MySQL there is a function called ROW_COUNT() that serves the same purpose (available as of version 5). Theoretically Jeremiah's suggestion should result in improved performance on MySQL also, but you should test it to make sure. Anonymous February 21, 2008 MySQL does...
delete语法(行视角) Drop 语法 Truncate table 语法 Update语法 Alter table 语句(列视角) 数据类型 二、高级教程 Top 语法(并非所有数据库都支持) Like 语法 SQL通配符(LIKE模式使用) In 语法 Between 语法 As 语法 Join 语法(列+列) Union 语法(行+行) Select into 语法 Create database 语法 Create table...
DELETE can be used in the body of a user-defined function if the object modified is a table variable.When you delete a row that contains a FILESTREAM column, you also delete its underlying file system files. The underlying files are removed by the FILESTREAM garbage collector. For more ...