manual.texi:

Update manual on ON DELETE CASCADE


Docs/manual.texi:
  Update manual on ON DELETE CASCADE

Docs/manual.texi

@@ -38066,23 +38066,50 @@ constraints to guard the integrity of your data.
 The syntax of a foreign key constraint definition in InnoDB:
 @example
 FOREIGN KEY (index_col_name, ...)
-  REFERENCES table_name (index_col_name, ...)
-@end example
-Starting from version 3.23.50 the InnoDB parser allows you to
-use backquotes (`) around table and column names in the above
-definition.
-
-An example:
-@example
-CREATE TABLE parent(id INT NOT NULL, PRIMARY KEY (id)) TYPE=INNODB;
-CREATE TABLE child(id INT, parent_id INT, INDEX par_ind (parent_id),
-             FOREIGN KEY (parent_id) REFERENCES parent(id)) TYPE=INNODB;
+                  REFERENCES table_name (index_col_name, ...)
+                  [ON DELETE CASCADE | ON DELETE SET NULL]
 @end example
 Both tables have to be InnoDB type and @strong{there must be an index
 where the foreign key and the referenced key are listed as the first
 columns}. InnoDB does not auto-create indexes on foreign keys or
 referenced keys: you have to create them explicitly.
 
+Corresponding columns in the foreign key
+and the referenced key must have similar internal data types
+inside InnoDB so that they can be compared without a type
+conversion.
+The size and the signedness of integer types has to be the same.
+The length of string types need not be the same.
+
+Starting from version 3.23.50 you can also associate the
+@code{ON DELETE CASCADE} or @code{ON DELETE SET NULL}
+clause with the foreign key constraint.
+
+If @code{ON DELETE CASCADE} is specified, and a row in the parent
+table is deleted, then InnoDB automatically deletes also all those rows
+in the child table whose foreign key values are equal to
+the referenced key value in the parent row. If @code{ON DELETE SET NULL}
+is specified, the child rows are automatiaclly updated so that the
+columns in the foreign key are set to the SQL NULL value.
+
+Starting from version 3.23.50, InnoDB does not check foreign key
+constraints on those foreign key or referenced key values
+which contain a NULL column.
+
+Starting from version 3.23.50 the InnoDB parser allows you to
+use backquotes (`) around table and column names in the above
+definition but the InnoDB parser is not yet aware of possible
+variable @code{lower_case_table_names} you give in @file{my.cnf}.
+
+An example:
+@example
+CREATE TABLE parent(id INT NOT NULL, PRIMARY KEY (id)) TYPE=INNODB;
+CREATE TABLE child(id INT, parent_id INT, INDEX par_ind (parent_id),
+             FOREIGN KEY (parent_id) REFERENCES parent(id)
+             ON DELETE SET NULL
+) TYPE=INNODB;
+@end example
+
 If MySQL gives the error number 1005 from a @code{CREATE TABLE}
 statement, and the error message string refers to errno 150, then
 the table creation failed because a foreign key constraint was not
@@ -38099,10 +38126,6 @@ ALTER TABLE yourtablename
 @end example
 Remember to create the required indexes first, though.
                            
-Starting from version 3.23.50, InnoDB does not check foreign key
-constraints on those foreign key or referenced key values
-which contain a NULL column.
-
 In InnoDB versions < 3.23.50 @code{ALTER TABLE}
 or @code{CREATE INDEX}
 should not be used in connection with tables which have foreign
@@ -38118,12 +38141,6 @@ A @code{CREATE INDEX} statement is in MySQL
 processed as an @code{ALTER TABLE}, and these
 restrictions apply also to it.
 
-Corresponding columns in the foreign key
-and the referenced key must have similar internal data types
-inside InnoDB so that they can be compared without a type
-conversion. The length of string types need not be the same.
-The size and the signedness of integer types has to be the same.
-
 When doing foreign key checks InnoDB sets shared row
 level locks on child or parent records it has to look at.
 InnoDB checks foreign key constraints immediately: the check