Comments

The methods for commenting on SQL statements and database objects are different.

Comments on SQL statements

For general SQL statements, OceanBase Database supports the following three commenting methods:

• From # to the end of the line, you can comment on a line.

• From -- to the end of the line, you can comment on a line.

• From /* to */, you can comment on multiple lines.

  Note

  SQL statements do not support nested comments.

In particular, OceanBase Database supports treating the statements within /*!*/ as SQL statements and executing the comments. If there is a syntax error within /*!*/, the database will default to treating it as a comment.

The format of a comment is as follows:

/*![Continuous numeric characters representing the version number] <space> <any SQL statement> */

• Example 1: Create a hash partitioned table named t1 with 8 partitions.

  obclient> CREATE TABLE t1 (c1 INT PRIMARY KEY, c2 INT) /*!50100
      PARTITION BY HASH(c1) PARTITIONS 8*/;
  Query OK, 0 rows affected
  

• Example 2: Use ENABLE KEYS to update non-unique indexes. When performing batch inserts, you can use DISABLE KEYS to temporarily skip index updates. After all indexes have been inserted, you can then update the indexes.

  obclient> /*!ALTER TABLE t1 DISABLE KEYS */;
  Query OK, 0 rows affected
  
  obclient> /*!ALTER TABLE t1 ENABLE KEYS */;
  Query OK, 0 rows affected
  

• Example 3: Supports the DROP IF EXISTS syntax in PL.

  obclient> /*!50003 DROP PROCEDURE IF EXISTS */;
  Query OK, 0 rows affected
  

Comments on database objects

In DDL statements, you can use the COMMENT clause to specify comments for database objects. Here is an example:

obclient> CREATE TABLE tbl1(pk INT PRIMARY KEY COMMENT 'Primary key');
Query OK, 0 rows affected