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You can't put SHOW statements inside a subquery like in your example. The only statement that can go in a subquery is SELECT.
As other answers have stated, you can query the INFORMATION_SCHEMA directly with SELECT and get a lot more flexibility that way.
MySQL's SHOW statements are internally just queries against the INFORMATION_SCHEMA tables.
User @physicalattraction has posted this comment on most other answers:
This gives you (meta)information about the tables, not the contents of the table, as the OP intended. – physicalattraction
On the contrary, the OP's question does not say that they want to select the data in all the tables. They say they want to select from the result of SHOW TABLES, which is just a list of table names.
If the OP does want to select all data from all tables, then the answer is no, you can't do it with one query. Each query must name its tables explicitly. You can't make a table name be a variable or the result of another part of the same query. Also, all rows of a given query result must have the same columns.
So the only way to select all data from all tables would be to run SHOW TABLES and then for each table named in that result, run another query.
Have you looked into querying INFORMATION_SCHEMA.Tables? As in
SELECT ic.Table_Name,
ic.Column_Name,
ic.data_Type,
IFNULL(Character_Maximum_Length,'') AS `Max`,
ic.Numeric_precision as `Precision`,
ic.numeric_scale as Scale,
ic.Character_Maximum_Length as VarCharSize,
ic.is_nullable as Nulls,
ic.ordinal_position as OrdinalPos,
ic.column_default as ColDefault,
ku.ordinal_position as PK,
kcu.constraint_name,
kcu.ordinal_position,
tc.constraint_type
FROM INFORMATION_SCHEMA.COLUMNS ic
left outer join INFORMATION_SCHEMA.key_column_usage ku
on ku.table_name = ic.table_name
and ku.column_name = ic.column_name
left outer join information_schema.key_column_usage kcu
on kcu.column_name = ic.column_name
and kcu.table_name = ic.table_name
left outer join information_schema.table_constraints tc
on kcu.constraint_name = tc.constraint_name
order by ic.table_name, ic.ordinal_position;
I don't understand why you want to use SELECT * FROM as part of the statement.