[Solved] You have this foreign key constraint:FOREIGN KEY (fk_col) REFERENCES parent(id) ON UPDATE CASCADEYou try to update the parent key but get an error. What could be a likely cause? | SQL

SQL - Table Constraints

You have this foreign key constraint:

FOREIGN KEY (fk_col) REFERENCES parent(id) ON UPDATE CASCADE

You try to update the parent key but get an error. What could be a likely cause?

AON UPDATE CASCADE is not supported by the database.

BThe child table has rows with fk_col values that do not match any parent id.

CThe parent key is not a primary key.

DThe foreign key column is not indexed.

Step-by-Step Solution

Solution:

Step 1: Check foreign key integrity
If child rows have fk_col values not matching any parent id, update can fail due to constraint violation.
Step 2: Understand ON UPDATE CASCADE requirements
ON UPDATE CASCADE requires existing matching keys; otherwise, update fails.
Final Answer:
The child table has rows with fk_col values that do not match any parent id. -> Option B
Quick Check:
Foreign key mismatch causes update error [OK]

Quick Trick: Foreign key mismatch causes update errors [OK]

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