#1215 SQL Cannot add foreign key constraint error [closed] - sql

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Here is my code. I can't figure out why I can't add the constraint.
Create table customer(
UserId Integer
)
CREATE TABLE Date(
DateID INTEGER,
User1ID INTEGER NOT NULL,
User2ID INTEGER NOT NULL,
Date CHAR(20) NOT NULL,
GeoLocation CHAR(20) NOT NULL,
BookingFee INTEGER NOT NULL,
CustomerRepresentative CHAR(20) NOT NULL,
Comments CHAR(200),
User1Ratings CHAR(20),
User2Ratings CHAR(20),
Primary Key (DateID),
Check ( User1Ratings IN (‘Excellent’, ‘VeryGood’, ‘Good’, ‘Fair’, ‘Poor’) ),
Check ( User2Ratings IN (‘Excellent’, ‘VeryGood’, ‘Good’, ‘Fair’, ‘Poor’) ),
FOREIGN KEY (User1ID) REFERENCES customer(UserID)
)

Answer 1

The most likely explanation for the behavior is that UserID column is not defined as the PRIMARY KEY or a UNIQUE KEY in the customer table
One fix for this would be to re-write the create for the customer table
For SQL Server:
CREATE TABLE customer
( UserId Integer NOT NULL
, CONSTRAINT PK_customer PRIMARY KEY CLUSTERED (UserId)
);
For MySQL:
CREATE TABLE customer
( UserId INTEGER NOT NULL PRIMARY KEY
);