NDB Cluster Configuration Files same type, including the same signedness, length, character set and collation, precision, and scale, where these are applicable. 2. Queries referencing  BLOB  or  TEXT  columns are not supported. 3. Explicit locking is not supported; however, the  NDB  storage engine’s characteristic implicit row-based locking is enforced. 4. In order for a join to be pushed down, child tables in the join must be accessed using one of the  ref , eq_ref , or const  access methods, or some combination of these methods. This means that a join using  FOR UPDATE  cannot be pushed down. Outer joined child tables can only be pushed using  eq_ref . If the root of the pushed join is an  eq_ref  or  const , only child tables joined by  eq_ref  can be appended. (A table joined by  ref  is likely to become the root of another pushed join.) If the query optimizer decides on  Using join cache  for a candidate child table, that table cannot be pushed as a child. However, it may be the root of another set of pushed tables. 5. Joins referencing tables explicitly partitioned by  [LINEAR] HASH ,  LIST , or  RANGE  currently cannot be pushed down. You can see whether a given join can be pushed down by checking it with  EXPLAIN ; when the join can be pushed down, you can see references to the  pushed join  in the  Extra  column of the output, as shown in this example: mysql>  EXPLAIN -> SELECT e.first_name, e.last_name, t.title, d.dept_name -> FROM employees e -> JOIN dept_emp de ON e.emp_no=de.emp_no -> JOIN departments d ON d.dept_no=de.dept_no -> JOIN titles t ON e.emp_no=t.emp_no\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: d type: ALL possible_keys: PRIMARY key: NULL key_len: NULL ref: NULL rows: 9 Extra: Parent of 4 pushed join@1 *************************** 2. row *************************** id: 1 select_type: SIMPLE table: de type: ref possible_keys: PRIMARY,emp_no,dept_no key: dept_no key_len: 4 ref: employees.d.dept_no rows: 5305 Extra: Child of ’d’ in pushed join@1 *************************** 3. row *************************** id: 1 select_type: SIMPLE table: e type: eq_ref possible_keys: PRIMARY 4181