
             Description
             Tests whether the table specified in in_db and in_table exists either as a regular
             table, or as a temporary table. The returned value corresponds to the table that
             will be used, so if there's both a temporary and a permanent table with the given
             name, then 'TEMPORARY' will be returned.
             Parameters
             in_db (VARCHAR(64)):
               The database name to check for the existence of the table in.
             in_table (VARCHAR(64)):
               The name of the table to check the existence of.
             out_exists ENUM('', 'BASE TABLE', 'VIEW', 'TEMPORARY'):
               The return value: whether the table exists. The value is one of:
                 * ''             - the table does not exist neither as a base table, view, sequence nor temporary table.
                 * 'BASE TABLE'   - the table name exists as a permanent base table table.
                 * 'VIEW'         - the table name exists as a view.
                 * 'TEMPORARY'    - the table name exists as a temporary table.
                 * 'SEQUENCE'     - the table name exists as a sequence.
                 * 'SYSTEM VIEW'  - the table name exists as a system view.
             Example
             mysql> CREATE DATABASE db1;
             Query OK, 1 row affected (0.07 sec)
             mysql> use db1;
             Database changed
             mysql> CREATE TABLE t1 (id INT PRIMARY KEY);
             Query OK, 0 rows affected (0.08 sec)
             mysql> CREATE TABLE t2 (id INT PRIMARY KEY);
             Query OK, 0 rows affected (0.08 sec)
             mysql> CREATE view v_t1 AS SELECT * FROM t1;
             Query OK, 0 rows affected (0.00 sec)
             mysql> CREATE TEMPORARY TABLE t1 (id INT PRIMARY KEY);
             Query OK, 0 rows affected (0.00 sec)
             mysql> CALL sys.table_exists('db1', 't1', @exists); SELECT @exists;
             Query OK, 0 rows affected (0.00 sec)
             +------------+
             | @exists    |
             +------------+
             | TEMPORARY  |
             +------------+
             1 row in set (0.00 sec)
             mysql> CALL sys.table_exists('db1', 't2', @exists); SELECT @exists;
             Query OK, 0 rows affected (0.00 sec)
             +------------+
             | @exists    |
             +------------+
             | BASE TABLE |
             +------------+
             1 row in set (0.01 sec)
             mysql> CALL sys.table_exists('db1', 'v_t1', @exists); SELECT @exists;
             Query OK, 0 rows affected (0.00 sec)
             +---------+
             | @exists |
             +---------+
             | VIEW    |
             +---------+
             1 row in set (0.00 sec)
             MariaDB [sys]> CALL sys.table_exists('db1', 's', @exists); SELECT @exists;
             Query OK, 0 rows affected (0.006 sec)
             +----------+
             | @exists  |
             +----------+
             | SEQUENCE |
             +----------+
             1 row in set (0.000 sec)
             MariaDB [sys]> CALL table_exists('information_schema', 'user_variables', @exists); SELECT @exists;
             Query OK, 0 rows affected (0.003 sec)
             +-------------+
             | @exists     |
             +-------------+
             | SYSTEM VIEW |
             +-------------+
             1 row in set (0.001 sec)
             mysql> CALL sys.table_exists('db1', 't3', @exists); SELECT @exists;
             Query OK, 0 rows affected (0.01 sec)
             +---------+
             | @exists |
             +---------+
             |         |
             +---------+
             1 row in set (0.00 sec)
            