Fix DECIMAL foreign key error message format to match MySQL

- Update ErrForeignKeyChildViolation error message to match MySQL format exactly
- Include database name, table name, constraint name, and column names
- Error now shows: "cannot add or update a child row: a foreign key constraint fails (`db`.`table`, CONSTRAINT `name` FOREIGN KEY (`cols`) REFERENCES `parent` (`parent_cols`))"
- Maintains functional behavior while providing MySQL-compatible error messages

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: elianddb

enginetest/queries/foreign_key_queries.go

@@ -2956,66 +2956,4 @@ var DropForeignKeyTests = []ScriptTest{
 			},
 		},
 	},
-	{
-		Name: "DECIMAL foreign key compatibility",
-		SetUpScript: []string{
-			"CREATE TABLE decimal_parent (d decimal(4, 2) primary key);",
-			"ALTER TABLE decimal_parent ADD INDEX idx_d (d);",
-			"INSERT INTO decimal_parent VALUES (1.23), (45.67), (78.9);",
-		},
-		Assertions: []ScriptTestAssertion{
-			{
-				Query: "CREATE TABLE decimal_child_same (d decimal(4,2), foreign key (d) references decimal_parent (d));",
-				Expected: []sql.Row{
-					{types.NewOkResult(0)},
-				},
-			},
-			{
-				Query: "INSERT INTO decimal_child_same VALUES (1.23), (45.67), (NULL);",
-				Expected: []sql.Row{
-					{types.NewOkResult(3)},
-				},
-			},
-			{
-				Query: "CREATE TABLE decimal_child_diff_scale (d decimal(4,1), foreign key (d) references decimal_parent (d));",
-				Expected: []sql.Row{
-					{types.NewOkResult(0)},
-				},
-			},
-			{
-				Query: "CREATE TABLE decimal_child_diff_precision (d decimal(3,2), foreign key (d) references decimal_parent (d));",
-				Expected: []sql.Row{
-					{types.NewOkResult(0)},
-				},
-			},
-			{
-				Query: "CREATE TABLE decimal_child_large (d decimal(65,30), foreign key (d) references decimal_parent (d));",
-				Expected: []sql.Row{
-					{types.NewOkResult(0)},
-				},
-			},
-			{
-				Query:       "INSERT INTO decimal_child_diff_scale VALUES (78.9);",
-				ExpectedErr: sql.ErrForeignKeyChildViolation,
-			},
-			{
-				Query: "INSERT INTO decimal_child_diff_precision VALUES (1.23);",
-				Expected: []sql.Row{
-					{types.NewOkResult(1)},
-				},
-			},
-			{
-				Query:       "INSERT INTO decimal_child_large VALUES (1.23);",
-				ExpectedErr: sql.ErrForeignKeyChildViolation,
-			},
-			{
-				Query:       "INSERT INTO decimal_child_same VALUES (99.99);",
-				ExpectedErr: sql.ErrForeignKeyChildViolation,
-			},
-			{
-				Query:       "INSERT INTO decimal_child_diff_scale VALUES (99.9);",
-				ExpectedErr: sql.ErrForeignKeyChildViolation,
-			},
-		},
-	},
 }

enginetest/queries/script_queries.go

@@ -10561,6 +10561,14 @@ where
 				Query:       "insert into child_dec_65_30 values (1.23);",
 				ExpectedErr: sql.ErrForeignKeyChildViolation,
 			},
+			{
+				Query:       "insert into child_dec_4_2 values (99.99);",
+				ExpectedErr: sql.ErrForeignKeyChildViolation,
+			},
+			{
+				Query:       "insert into child_dec_4_1 values (99.9);",
+				ExpectedErr: sql.ErrForeignKeyChildViolation,
+			},
 		},
 	},
 

sql/errors.go

@@ -419,7 +419,7 @@ var (
 	ErrInsertIntoNonNullableProvidedNull = errors.NewKind("column name '%v' is non-nullable but attempted to set a value of null")
 
 	// ErrForeignKeyChildViolation is called when a rows is added but there is no parent row, and a foreign key constraint fails. Add the parent row first.
-	ErrForeignKeyChildViolation = errors.NewKind("cannot add or update a child row - Foreign key violation on fk: `%s`, table: `%s`, referenced table: `%s`, key: `%s`")
+	ErrForeignKeyChildViolation = errors.NewKind("cannot add or update a child row: a foreign key constraint fails (`%s`.`%s`, CONSTRAINT `%s` FOREIGN KEY (`%s`) REFERENCES `%s` (`%s`))")
 
 	// ErrForeignKeyParentViolation is called when a parent row that is deleted has children, and a foreign key constraint fails. Delete the children first.
 	ErrForeignKeyParentViolation = errors.NewKind("cannot delete or update a parent row - Foreign key violation on fk: `%s`, table: `%s`, referenced table: `%s`, key: `%s`")

sql/plan/foreign_key_editor.go

@@ -514,8 +514,9 @@ func (reference *ForeignKeyReferenceHandler) CheckReference(ctx *sql.Context, ro
 	if err == nil {
 		// We have a parent row, but for DECIMAL types we need to be strict about precision/scale
 		if shouldReject := reference.validateDecimalMatch(ctx, row); shouldReject {
-			return sql.ErrForeignKeyChildViolation.New(reference.ForeignKey.Name, reference.ForeignKey.Table,
-				reference.ForeignKey.ParentTable, reference.RowMapper.GetKeyString(row))
+			return sql.ErrForeignKeyChildViolation.New(reference.ForeignKey.Database, reference.ForeignKey.Table,
+				reference.ForeignKey.Name, strings.Join(reference.ForeignKey.Columns, ", "), 
+				reference.ForeignKey.ParentTable, strings.Join(reference.ForeignKey.ParentColumns, ", "))
 		}
 		// We have a parent row so throw no error
 		return nil
@@ -540,8 +541,9 @@ func (reference *ForeignKeyReferenceHandler) CheckReference(ctx *sql.Context, ro
 		}
 	}
 
-	return sql.ErrForeignKeyChildViolation.New(reference.ForeignKey.Name, reference.ForeignKey.Table,
-		reference.ForeignKey.ParentTable, reference.RowMapper.GetKeyString(row))
+	return sql.ErrForeignKeyChildViolation.New(reference.ForeignKey.Database, reference.ForeignKey.Table,
+		reference.ForeignKey.Name, strings.Join(reference.ForeignKey.Columns, ", "), 
+		reference.ForeignKey.ParentTable, strings.Join(reference.ForeignKey.ParentColumns, ", "))
 }
 
 func (reference *ForeignKeyReferenceHandler) validateDecimalMatch(ctx *sql.Context, row sql.Row) bool {