superset db upgrade returns foreign key constraint is incorrectly formed

superset db upgrade returns foreign key constraint is incorrectly formed. here is the log:

sqlalchemy.exc.OperationalError: (MySQLdb._exceptions.OperationalError) (1005, 'Can\'t create table `apache_superset`.`tab_state` (errno: 150 "Foreign key constraint is incorrectly formed")')
[SQL: 
CREATE TABLE tab_state (
	created_on DATETIME, 
	changed_on DATETIME, 
	extra_json TEXT, 
	id INTEGER NOT NULL AUTO_INCREMENT, 
	user_id INTEGER, 
	label VARCHAR(256), 
	active BOOL, 
	database_id INTEGER, 
	`schema` VARCHAR(256), 
	`sql` TEXT, 
	query_limit INTEGER, 
	latest_query_id VARCHAR(11), 
	autorun BOOL NOT NULL, 
	template_params TEXT, 
	created_by_fk INTEGER, 
	changed_by_fk INTEGER, 
	PRIMARY KEY (id), 
	FOREIGN KEY(changed_by_fk) REFERENCES ab_user (id), 
	FOREIGN KEY(created_by_fk) REFERENCES ab_user (id), 
	FOREIGN KEY(database_id) REFERENCES dbs (id), 
	FOREIGN KEY(latest_query_id) REFERENCES query (client_id), 
	FOREIGN KEY(user_id) REFERENCES ab_user (id), 
	CHECK (active IN (0, 1)), 
	CHECK (autorun IN (0, 1))
)

]
(Background on this error at: http://sqlalche.me/e/e3q8)

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[gregmazur]

SHOW CREATE TABLE query; check the charset Also might be useful for someone "mysql+pymysql://user:pass@host:3306/db?charset=<your query table charset>