merge Table Function

Creates a temporary Merge table. The structure will be derived from underlying tables by using a union of their columns and by deriving common types.

Syntax

Argument	Description
`db_name`	Possible values (optional, default is `currentDatabase()`): - database name, - constant expression that returns a string with a database name, for example, `currentDatabase()`, - `REGEXP(expression)`, where `expression` is a regular expression to match the DB names.
`tables_regexp`	A regular expression to match the table names in the specified DB or DBs.