Comments

Comments within SQL statements and database objects are specified in different ways.

Comments within SQL statements

OceanBase Database allows you to add comments in general SQL statements by using one of the following three methods:

• Start the comment with a number sign (#) and end it with a line break. The comment text cannot extend to a new line.

• Start the comment with two hyphens (--) and end it with a line break. The comment text cannot extend to a new line.

• Start the comment with a slash and an asterisk (/*) and end it with an asterisk and a slash (*/). The comment text can span multiple lines.

  Note

  SQL statements do not support nested comments.

In particular, OceanBase Database can execute statements in /*! */ as SQL statements. If a syntax error occurs in /*! */, OceanBase Database processes it as a comment by default.

The comment format is as follows:

/*![Consecutive numeric characters representing the version]<Space><Any SQL statement>*/

• Example 1: Create eight HASH partitions for table t1.

  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. During batch insertion, you can use DISABLE KEYS to postpone the update until all indexes are 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: The DROP IF EXISTS syntax of PL is supported.

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

Comments for database objects

You can use a COMMENT clause in a DDL statement to specify comments for a database object. Here is an example:

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