SET sql_mode=ORACLE;
SELECT SUBSTR('abc',2,1),SUBSTR('abc',1,1), SUBSTR('abc',0,1) FROM dual;
SUBSTR('abc',2,1)	SUBSTR('abc',1,1)	SUBSTR('abc',0,1)
b	a	a
SELECT SUBSTR('abc',2),SUBSTR('abc',1), SUBSTR('abc',0) FROM dual;
SUBSTR('abc',2)	SUBSTR('abc',1)	SUBSTR('abc',0)
bc	abc	abc
SELECT SUBSTR(null,2,1),SUBSTR(null,1), SUBSTR(null,0) FROM dual;
SUBSTR(null,2,1)	SUBSTR(null,1)	SUBSTR(null,0)
NULL	NULL	NULL
SELECT SUBSTR('abc',-2),SUBSTR('abc',-1), SUBSTR('abc',-0) FROM dual;
SUBSTR('abc',-2)	SUBSTR('abc',-1)	SUBSTR('abc',-0)
bc	c	abc
SELECT SUBSTR('abc',-2,1),SUBSTR('abc',-1,1), SUBSTR('abc',-0,1) FROM dual;
SUBSTR('abc',-2,1)	SUBSTR('abc',-1,1)	SUBSTR('abc',-0,1)
b	c	a
SELECT SUBSTR('abc',null) FROM dual;
SUBSTR('abc',null)
NULL
SELECT SUBSTR('abc',2,null),SUBSTR('abc',1,null), SUBSTR('abc',0,null) FROM dual;
SUBSTR('abc',2,null)	SUBSTR('abc',1,null)	SUBSTR('abc',0,null)
NULL	NULL	NULL
SELECT SUBSTR('abc',2,0),SUBSTR('abc',1,0), SUBSTR('abc',0,0) FROM dual;
SUBSTR('abc',2,0)	SUBSTR('abc',1,0)	SUBSTR('abc',0,0)
		
create table t1 (c1 varchar(10),start integer, length integer);
INSERT INTO t1 VALUES ('abc', 1, 1);
INSERT INTO t1 VALUES ('abc', 0, 1);
INSERT INTO t1 VALUES (null, 1, 1);
INSERT INTO t1 VALUES (null, 0, 1);
select substr(c1,start,length) from t1;
substr(c1,start,length)
a
a
NULL
NULL
drop table t1;
EXPLAIN EXTENDED SELECT SUBSTR('abc',2,1) ;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
Warnings:
Note	1003	select substr_oracle('abc',2,1) AS "SUBSTR('abc',2,1)"
CREATE VIEW v1 AS SELECT SUBSTR('abc',2,1) ;
SHOW CREATE VIEW v1;
View	Create View	character_set_client	collation_connection
v1	CREATE VIEW "v1" AS select substr_oracle('abc',2,1) AS "SUBSTR('abc',2,1)"	latin1	latin1_swedish_ci
SELECT * FROM v1;
SUBSTR('abc',2,1)
b
DROP VIEW v1;