So I'm kind of stumped.

I have a MySql project that involves a database table that is being manipulated and altered by scripts on a regular basis. This isn't so unusual, but I need to automate a script to run (after hours, when changes aren't happening) that would save the result of the following:

SHOW CREATE TABLE [table-name];

This command generates the ready-to-run script that would create the (empty) table in it's current state.

In SqlWorkbench and Navicat it displays the result of this SHOW command in a field in a result set, as if it was the result of a SELECT statement.

Ideally, I want to take into a variable in a procedure, and change the table name; adding a '-mm-dd-yyyy' to end of it, so I could show the day-to-day changes in the table schema on an active server.

However, I can't seem to be able to do that. Unlike a Select result set, I can't use it like that. I can't get it in a variable, or save it to a temporary, or physical table or anything. I even tried to return this as a value in a function, from which I got the error that a function cannot return a result set - which explains why it's displayed like one in the db clients.

I suspect that this is a security thing in MySql? If so, I can totally understand why and see the dangers exposed to a hacker, but this isn't a public-facing box at all, and I have full root/admin access to it. Hopefully somebody has already tackled this problem before.

This is on MySql 8, btw.

[Edit] After my first initial comments, I need to add; I'm not concerned about the data with this question whatsoever, but rather just these schema changes.

What I'd really -like- to do is this:

SELECT `Create Table` FROM ( SHOW  CREATE TABLE carts )

But this seems to be mixing apples and oranges, as SHOW and SELECT aren't created equal, although they both seem to return the same sort of object

CodePudding user response：

You cannot do it in the MySQL stored procedure language.

https://dev.mysql.com/doc/refman/8.0/en/show.html says:

Many MySQL APIs (such as PHP) enable you to treat the result returned from a SHOW statement as you would a result set from a SELECT; see Chapter 29, Connectors and APIs, or your API documentation for more information. In addition, you can work in SQL with results from queries on tables in the INFORMATION_SCHEMA database, which you cannot easily do with results from SHOW statements. See Chapter 26, INFORMATION_SCHEMA Tables.

What is absent from this paragraph is any mention of treating the results of SHOW commands like the results of SELECT queries in other contexts. There is no support for setting a variable to the result of a SHOW command, or using INTO, or running SHOW in a subquery.

So you can capture the result returned by a SHOW command in a client programming language (Java, Python, PHP, etc.), and I suggest you do this.

In theory, all the information used by SHOW CREATE TABLE is accessible in the INFORMATION_SCHEMA tables (mostly TABLES and COLUMNS), but formatting a complete CREATE TABLE statement is a non-trivial exercise, and I wouldn't attempt it. For one thing, there are new features in every release of MySQL, e.g. new data types and table options, etc. So even if you could come up with the right query to produce this output, in a couple of years it would be out of date and it would be a thankless code maintenance chore to update it.

CodePudding user response：

The closest solution I can think of, in pure MySQL, is to regularly clone the table structure (no data), like so:

CREATE TABLE backup_20220618 LIKE my_table;

As far as I know, to get your hands on the full explicit CREATE TABLE statement, as a string, would require the use of an external tool like mysqldump which was designed specifically for that purpose.