ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails That I can't fix

Question

I am getting this error :

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint 
fails (\`GTFS\`.\`#sql-37d_16\`, CONSTRAINT \`#sql-37d_16_ibfk_1\` FOREIGN KEY 
(\`service_id\`) REFERENCES \`calendar\` (\`service_id\`))

I'm trying to create my database tables with python , this is what i've tried :

mycursor.execute("CREATE TABLE IF NOT EXISTS routes(route_id  varchar(3) PRIMARY KEY, agency_id varchar(2) ,route_short_name varchar(20) ,route_long_name varchar(50) ,route_desc varchar(30) ,route_type varchar(30) ,route_url varchar(30) ,route_color varchar(30) ,route_text_color varchar(30)) ")

mycursor.execute("CREATE TABLE IF NOT EXISTS calendar (service_id varchar(4) PRIMARY KEY,monday varchar(4) ,tuesday varchar(4) ,wednesday varchar(4) ,thursday varchar(4) ,friday  varchar(4) ,saturday varchar(4) ,sunday varchar(4) ,start_date varchar(8) ,end_date varchar(8)) ")

mycursor.execute("CREATE TABLE IF NOT EXISTS trips (route_id varchar(3) ,service_id varchar(4) ,trip_id varchar(6) PRIMARY KEY,trip_headsign varchar(20) ,trip_short_name varchar(3) ,direction_id varchar(1) ,block_id varchar(1) ,shape_id varchar(5) )")

mycursor.execute("ALTER TABLE trips ADD FOREIGN KEY (service_id) REFERENCES calendar(service_id); ")

mycursor.execute("ALTER TABLE trips ADD FOREIGN KEY (route_id) REFERENCES routes(route_id); ")

I'm expecting to insert into my table some data provided in a list but i always get this error in my terminal

Answer 1

Because some values for trips.service_id column don't exist in the parent( calendar ) table for the common column service_id .

You may try to insert those values by such a insert statement :

insert into calendar(...,service_id,...) 
select ...,service_id,... 
  from trips t
 where not exists ( select 0 from calendar where service_id=t.service_id );

before adding the constraint by

ALTER TABLE trips ADD FOREIGN KEY (service_id) REFERENCES calendar(service_id);