[GitHub] incubator-hawq pull request: HAWQ-293. Enable writable external ta...

[zhangh43 <gi...@git.apache.org>]

Github user zhangh43 commented on a diff in the pull request:

    https://github.com/apache/incubator-hawq/pull/229#discussion_r48809821
  
    --- Diff: src/backend/commands/tablecmds.c ---
    @@ -17666,6 +17666,12 @@ static Datum transformExecOnClause(List	*on_clause, int *preferred_segment_num)
     		}
     		else if (strcmp(defel->defname, "master") == 0)
     		{
    +			if(iswritable){
    +			  ereport(ERROR,
    +	 	      (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
    +			    errmsg("the ON master syntax for writable external tables is deprecated"),
    --- End diff --
    
    Only ON number is allowed, e.g. ON 3 will start 3 virtual segments to run the query.
    
    Here's an example to create a writable external table in Hawq 2.0:
    postgres=# create table a (i int);
    CREATE TABLE
    postgres=# insert into a values(1);
    INSERT 0 1
    postgres=# insert into a values(2);
    INSERT 0 1
    postgres=# insert into a values(10);
    INSERT 0 1
    postgres=# CREATE WRITABLE EXTERNAL WEB TABLE externala (output text)         EXECUTE 'cat > /tmp/externala' on 3 FORMAT 'TEXT'   DISTRIBUTED RANDOMLY;
    CREATE EXTERNAL TABLE
    postgres=# insert into externala select * from a;
    INSERT 0 3
    
    You can check the result file in /tmp/externala:
    1
    2
    10


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