MySQL:如果存在IF表，则截断并插入ELSE创建 [英] MySQL: IF table exists, truncate and insert ELSE create

问题描述

仅使用MySQL(我本质上没有PHP知识)，我需要有一个表，该表本质上是更大表的子集.源表不时更改，丢失一些条目，获得其他新条目，并且为现有条目更改值.我可以描述我想发生的事情，但是似乎无法弄清楚使它起作用的命令语法.我也知道我可以有两个独立的查询，并且可以运行我需要的任何一个查询，而且已经解决了，但是我想尽可能地将它们合并.这就是我想要的:

Working only with MySQL (I have essentially no PHP knowledge), I need to have a table that's essentially a subset from a much larger table. The source table changes from time to time, losing some entries, gaining other new ones, and values changing for existing ones. I can describe what I want to happen, but can't seem to figure out a syntax of commands to make it work. I also know I can have two separate queries and just run whichever one I need, and I have that worked out, but I'd like to combine them if possible. Here's what I want:

如果不存在subset_table，请将其创建为[选择查询]，否则将截断subset_table并插入[选择查询]

IF the subset_table DOES NOT EXIST, create it as [select query], ELSE truncate the subset_table and insert [select query]

就像我说的那样，我知道还有其他方法可以执行此操作-如果存在/创建，我可以删除它，或者我可以只运行两个不同的sql文件.我只想知道我是否可以按照上面的说明进行操作.

Like I said, I know there are other ways to do this - I could drop if exists/create, or I could just have two different sql files to run. I just want to know if I can do this as specified above.

有想法吗?

推荐答案

您可以执行以下操作:

create table if not exists <tablename> . . .;

truncate table <tablename>;

insert into <tablename>(cols)
    select blah blahblah . . .;

您根本不需要任何if语句.

You don't need any if statements at all.

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