Functions that can be used on SEQUENCEs
LASTVAL
is a synonym for PREVIOUS VALUE for sequence_name.
This page is licensed: CC BY-SA / Gnu FDL
NEXT VALUE FOR sequence
or
NEXTVAL(sequence_name)
or in Oracle mode (SQL_MODE=ORACLE)
sequence_name.nextval
NEXT VALUE FOR
is ANSI SQL syntax while NEXTVAL()
is PostgreSQL syntax.
Generate next value for a SEQUENCE
.
You can greatly speed up NEXT VALUE
by creating the sequence with the CACHE
option. If not, every NEXT VALUE
usage will cause changes in the stored SEQUENCE
table.
When using NEXT VALUE
the value will be reserved at once and will not be reused, except if the SEQUENCE
was created with CYCLE
. This means that when you are using SEQUENCE
s you have to expect gaps in the generated sequence numbers.
If one updates the SEQUENCE
with SETVAL() or ALTER SEQUENCE ... RESTART, NEXT VALUE FOR
will notice this and start from the next requested value.
FLUSH TABLES will close the sequence and the next sequence number generated will be according to what's stored in the SEQUENCE
object. In effect, this will discard the cached values.
A server restart (or closing the current connection) also causes a drop of all cached values. The cached sequence numbers are reserved only for the current connection.
NEXT VALUE
requires the INSERT
privilege.
You can also use NEXT VALUE FOR sequence
for column DEFAULT
.
Once the sequence is complete, unless the sequence has been created with the CYCLE attribute (not the default), calling the function will result in Error 4084: Sequence has run out.
CREATE OR REPLACE SEQUENCE s MAXVALUE=2;
SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
| 1 |
+------------+
SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
| 2 |
+------------+
SELECT NEXTVAL(s);
ERROR 4084 (HY000): Sequence 'test.s' has run out
ALTER SEQUENCE s MAXVALUE=2 CYCLE;
SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
| 1 |
+------------+
SETVAL(). Set next value for the sequence.
This page is licensed: CC BY-SA / Gnu FDL
NEXTVAL
is a synonym for NEXT VALUE for sequence_name.
This page is licensed: CC BY-SA / Gnu FDL
PREVIOUS VALUE FOR sequence_name
or
LASTVAL(sequence_name)
or in Oracle mode (SQL_MODE=ORACLE)
sequence_name.currval
PREVIOUS VALUE FOR
is IBM DB2 syntax while LASTVAL()
is PostgreSQL syntax.
Gets the most recent value in the current connection generated from a sequence.
If the sequence has not yet been used by the connection, PREVIOUS VALUE FOR
returns NULL
(the same thing applies with a new connection which doesn't see a last value for an existing sequence).
If a SEQUENCE
has been dropped and re-created then it's treated as a new SEQUENCE
and PREVIOUS VALUE FOR
will return NULL
.
Returns NULL
if the sequence is complete
FLUSH TABLES has no effect on PREVIOUS VALUE FOR
.
Previous values for all used sequences are stored per connection until connection ends.
PREVIOUS VALUE FOR
requires the SELECT privilege.
CREATE SEQUENCE s START WITH 100 INCREMENT BY 10;
SELECT PREVIOUS VALUE FOR s;
+----------------------+
| PREVIOUS VALUE FOR s |
+----------------------+
| NULL |
+----------------------+
# The function works for sequences only, if the table is used an error is generated
SELECT PREVIOUS VALUE FOR t;
ERROR 4089 (42S02): 'test.t' is not a SEQUENCE
# Call the NEXT VALUE FOR s:
SELECT NEXT VALUE FOR s;
+------------------+
| NEXT VALUE FOR s |
+------------------+
| 100 |
+------------------+
SELECT PREVIOUS VALUE FOR s;
+----------------------+
| PREVIOUS VALUE FOR s |
+----------------------+
| 100 |
+----------------------+
Now try to start the new connection and check that the last value is still NULL, before updating the value in the new connection after the output of the new connection gets current value (110 in the example below). Note that first connection cannot see this change and the result of last value still remains the same (100 in the example above).
$ .mysql -uroot test -e"SELECT PREVIOUS VALUE FOR s; SELECT NEXT VALUE FOR s; SELECT PREVIOUS VALUE FOR s;"
+----------------------+
| PREVIOUS VALUE FOR s |
+----------------------+
| NULL |
+----------------------+
+------------------+
| NEXT VALUE FOR s |
+------------------+
| 110 |
+------------------+
+----------------------+
| PREVIOUS VALUE FOR s |
+----------------------+
| 110 |
+----------------------+
Returns NULL if the sequence has run out:
CREATE OR REPLACE SEQUENCE s MAXVALUE=2;
SELECT NEXTVAL(s), LASTVAL(s);
+------------+------------+
| NEXTVAL(s) | LASTVAL(s) |
+------------+------------+
| 1 | 1 |
+------------+------------+
SELECT NEXTVAL(s), LASTVAL(s);
+------------+------------+
| NEXTVAL(s) | LASTVAL(s) |
+------------+------------+
| 2 | 2 |
+------------+------------+
SELECT NEXTVAL(s), LASTVAL(s);
ERROR 4084 (HY000): Sequence 'test.s' has run out
SELECT LASTVAL(s);
+------------+
| LASTVAL(s) |
+------------+
| NULL |
+------------+
SETVAL(). Set next value for the sequence.
This page is licensed: CC BY-SA / Gnu FDL
SETVAL(sequence_name, next_value, [is_used, [round]])
Set the next value to be returned for a SEQUENCE
.
This function is compatible with PostgreSQL syntax, extended
with the round
argument.
If the is_used
argument is not given or is 1
or true
, then the next used value will
one after the given value. If is_used
is 0
or false
then the next generated value
will be the given value.
If round
is used then it will set the round
value (or the internal cycle count, starting at zero) for the sequence.
If round
is not used, it's assumed to be 0.
next_value
must be an integer literal.
For SEQUENCE
tables defined with CYCLE
(see CREATE SEQUENCE) one should use both next_value
and round
to define the next value. In this case the
current sequence value is defined to be round
, next_value
.
The result returned by SETVAL()
is next_value
or NULL if the given next_value
and round
is smaller than the current value.
SETVAL()
will not set the SEQUENCE
value to a something that is less than
its current value. This is needed to ensure that SETVAL()
is replication safe. If you want to set the SEQUENCE to a smaller number
use ALTER SEQUENCE.
If CYCLE
is used, first round
and then next_value
are compared
to see if the value is bigger than the current value.
Internally, in the MariaDB server, SETVAL()
is used to inform
replicas that a SEQUENCE
has changed value. The replica may getSETVAL()
statements out of order, but this is ok as only the
biggest one will have an effect.
SETVAL
requires the INSERT privilege.
SELECT setval(foo, 42); -- Next nextval will return 43
SELECT setval(foo, 42, true); -- Same as above
SELECT setval(foo, 42, false); -- Next nextval will return 42
SETVAL setting higher and lower values on a sequence with an increment of 10:
SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
| 50 |
+------------+
SELECT SETVAL(s, 100);
+----------------+
| SETVAL(s, 100) |
+----------------+
| 100 |
+----------------+
SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
| 110 |
+------------+
SELECT SETVAL(s, 50);
+---------------+
| SETVAL(s, 50) |
+---------------+
| NULL |
+---------------+
SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
| 120 |
+------------+
Example demonstrating round
:
CREATE OR REPLACE SEQUENCE s1
START WITH 1
MINVALUE 1
MAXVALUE 99
INCREMENT BY 1
CACHE 20
CYCLE;
SELECT SETVAL(s1, 99, 1, 0);
+----------------------+
| SETVAL(s1, 99, 1, 0) |
+----------------------+
| 99 |
+----------------------+
SELECT NEXTVAL(s1);
+-------------+
| NEXTVAL(s1) |
+-------------+
| 1 |
+-------------+
The following statement returns NULL, as the given next_value
and round
is smaller than the current value.
SELECT SETVAL(s1, 99, 1, 0);
+----------------------+
| SETVAL(s1, 99, 1, 0) |
+----------------------+
| NULL |
+----------------------+
SELECT NEXTVAL(s1);
+-------------+
| NEXTVAL(s1) |
+-------------+
| 2 |
+-------------+
Increasing the round from zero to 1 will allow next_value
to be returned.
SELECT SETVAL(s1, 99, 1, 1);
+----------------------+
| SETVAL(s1, 99, 1, 1) |
+----------------------+
| 99 |
+----------------------+
SELECT NEXTVAL(s1);
+-------------+
| NEXTVAL(s1) |
+-------------+
| 1 |
+-------------+
This page is licensed: CC BY-SA / Gnu FDL