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 methods for commenting:

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

• From -- to the end of the line, you can comment on one 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 treat it as a regular 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 bulk inserts, you can use DISABLE KEYS to temporarily skip index updates and update the indexes after all data has been inserted.

  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