Question

I have table T1 where col A is primary key and col B is a foreign key which is a primary key in table T2. I want to create an index in T1, a composite one as (B,A). But MySQL is allowing me to create the index as (A,B) only. Is it because col B is a foreign key ?? Please explain

Answer 1

This works fine for me:

CREATE TABLE t2 (id INT NOT NULL PRIMARY KEY) ENGINE=InnoDB;
CREATE TABLE t1 (a INT NOT NULL PRIMARY KEY, b INT NOT NULL REFERENCES t2(id)) ENGINE=InnoDB;
CREATE INDEX ix_t1_b_a ON t1 (b, a);

Though InnoDB does include clustered key as a row pointer in the indexes, there is nothing that prevents adding the field explicitly and sometimes it is required to optimize some queries.

Please check your syntax.