Using Global Sequences in INSERT or REPLACE Statements

You can use global sequences in INSERT or REPLACE statements to provide unique global sequence across schemas in a DDM instance. Generating sequence numbers with NEXTVAL and CURRVAL is supported in INSERT or REPLACE statements. NEXTVAL returns the next sequence number, and CURRVAL returns the current sequence number, for example, schema.seq.nextval and schema.seq.currval. If no schema is specified, use the global sequence of the currently connected schema.

Concurrently executing schema.seq.nextval in multiple sessions is supported to obtain unique global sequence numbers.

Prerequisites

There are two schemas dml_test_1 and dml_test_2.
Both of them have table test_seq.
Run the following command to create a table:

create table test_seq(col1 bigint,col2 bigint) dbpartition by hash(col1);

Procedure

Connect to a DDM instance.
For details, see Connecting to a DDM Instance.
Log in to schema dml_test_1.
use dml_test_1;
Run the following command to create a global sequence:
create sequence seq_test;
Run the following statement to use the global sequence in an INSERT or REPLACE statement:
insert into test_seq(col1,col2)values(seq_test.nextval,seq_test.currval);
Log in to schema dml_test_2.
use dml_test_2;
Run the following statement to use the global sequence in an INSERT or REPLACE statement:
insert into test_seq(col1,col2)values(dml_test_1.seq_test.nextval,dml_test_1.seq_test.currval);

The global sequence is created in schema dml_test_1. To use the global sequence in schema dml_test_2, you need to specify a schema name, for example, dml_test_1.seq_test.nextval or dml_test_1.seq_test.currval.
- Using global sequences in INSERT and REPLACE statements is supported only in sharded tables, but not in broadcast or unsharded tables.
- NEXTVAL and CURRVAL are executed from left to right in INSERT and REPLACE statements. If NEXTVAL is referenced more than once in a single statement, the sequence number is incremented for each reference.
- Each global sequence belongs to a schema. When you delete a schema, the global sequence of the schema is also deleted.