A primary key is not needed, but a unique constraint at minimum.

CREATE TABLE GIS_Data

(ParcelID int)

CREATE TABLE Field_Data

(ParcelID int)

INSERT into GIS_Data

select 1 union

select 2 union

select 3 union

select 4 union

select 5 union

select 6

INSERT into Field_Data

select 4 union

select 5 union

select 6 union

select 7 union

select 8 union

select 9

CREATE UNIQUE NONCLUSTERED INDEX IX_Field_Data ON dbo.Field_Data

(ParcelID)

ALTER TABLE GIS_DATA

ADD CONSTRAINT FK_FIELD_DATA FOREIGN KEY (ParcelID)

REFERENCES Field_Data (ParcelID)

--These records have not match in the Field_Data table

SELECT ParcelID

FROM GIS_Data WHERE ParcelID NOT IN (SELECT ParcelID from Field_Data)

--They must be updated or deleted from GIS_Data, or inserted int Field_Data

BEGIN TRAN

DELETE FROM GIS_Data WHERE ParcelID NOT IN (SELECT ParcelID from Field_Data)

ALTER TABLE GIS_Data

ADD CONSTRAINT FK_FIELD_DATA FOREIGN KEY (ParcelID)

REFERENCES Field_Data (ParcelID)

ROLLBACK

BEGIN TRAN

INSERT INTO Field_Data

SELECT ParcelID FROM GIS_Data WHERE ParcelID NOT IN (SELECT ParcelID from Field_Data)

ALTER TABLE GIS_Data

ADD CONSTRAINT FK_FIELD_DATA FOREIGN KEY (ParcelID)

REFERENCES Field_Data (ParcelID)

ROLLBACK

DROP TABLE GIS_Data

DROP TABLE Field_Data