SQL IF表A是表B中的空副本列

So here is the perfectly working query I need to run though short of the necessary condition:

所以这里是我需要运行的完美工作查询,但缺少必要条件:

INSERT INTO content (`id`,`id_pages`,`content`, `date`) 
SELECT `id`, `id`, `content`, `date_modified` FROM `pages`;

Unfortunately not all the databases are synced properly so some of the tables are populated and some are not.

遗憾的是,并非所有数据库都已正确同步,因此某些表格已填充,而某些表格则未填充。

How do I INSERT data from table A to table B IF table A is empty?

如何将表A中的数据插入表B如果表A为空?

A couple queries I've tried:

我试过几个查询:

IF (
SELECT count(id) FROM content='0',
INTO content (`id`,`id_pages`,`content`, `date`)
SELECT `id`, `id`, `content`, `date_modified` FROM `pages`)

...as well as:

...以及:

IF (SELECT count(id) FROM content)=0 
THEN (INSERT INTO content (`id`,`id_pages`,`content`, `date`)
SELECT `id`, `id`, `content`, `date_modified` FROM `pages`);

1 个解决方案

#1

Try this:

INSERT INTO content (`id`,`id_pages`,`content`, `date`)
SELECT `id`, `id`, `content`, `date_modified` 
FROM `pages`
WHERE NOT EXISTS (SELECT 1 FROM content)

The SELECT of the above INSERT statement will return all pages records unless there is at least on record in content table.

除非内容表中至少有记录,否则上述INSERT语句的SELECT将返回所有页面记录。

Demo with empty table | Demo with not empty table

用空表演示|演示没有空表

#1