How do I drop a foreign key constraint only if it exists in sql server?

In SQL Server 2016 you can use DROP IF EXISTS:

CREATE TABLE t(id int primary key,
parentid int
constraint tpartnt foreign key references t(id))
GO
ALTER TABLE t
DROP CONSTRAINT IF EXISTS tpartnt
GO
DROP TABLE IF EXISTS t

See

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All table constraints will be stored in INFORMATION_SCHEMA.TABLE_CONSTRAINTS

IF EXISTS(SELECT * FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS C WHERE C.CONSTRAINT_NAME = '<CONSTRAINT NAME>' AND C.TABLE_NAME = '<TABLE NAME>')
BEGIN
ALTER TABLE <TABLE NAME>
DROP CONSTRAINT <CONSTRAINT NAME>
END
GO

This worked smoothly for Azure Sql server:

```sql
IF (OBJECT_ID('dbo.FK_company_id', 'F') IS NOT NULL)
BEGIN
ALTER TABLE dbo.table_company DROP CONSTRAINT FK_company_id
END
```