create table t1

(

	PARENT_ID int(10) unsigned NOT NULL AUTO_INCREMENT,

	PARENT_FIELD VARCHAR(10),

	PRIMARY KEY (PARENT_ID)

);

create table t2

(

	CHILD_ID INT NOT NULL AUTO_INCREMENT,

	PARENT_ID INT NOT NULL,

	CHILD_FIELD varchar(10),

	PRIMARY KEY (CHILD_ID)

);

INSERT INTO t1 (PARENT_FIELD)

SELECT 'AAAA';

INSERT INTO t2 (PARENT_ID, CHILD_FIELD)

SELECT 1, 'BBBB';

select

 t1.PARENT_ID,

 min(CHILD_FIELD)

 from t1 straight_join t2

 where t1.PARENT_ID = 1

 and t1.PARENT_ID = t2.PARENT_ID

 and t2.CHILD_FIELD = "ZZZZ";

DROP TABLES t1, t2;

PARENT_ID	min(CHILD_FIELD)

NULL	NULL

PARENT_ID	min(CHILD_FIELD)

0	NULL