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From dyozie <...@git.apache.org>
Subject [GitHub] incubator-hawq-docs pull request #101: HAWQ-1383 - plpgsql page cleanup, res...
Date Fri, 10 Mar 2017 17:45:38 GMT
Github user dyozie commented on a diff in the pull request:

    https://github.com/apache/incubator-hawq-docs/pull/101#discussion_r105438584
  
    --- Diff: markdown/plext/using_plpgsql.html.md.erb ---
    @@ -19,143 +19,278 @@ software distributed under the License is distributed on an
     KIND, either express or implied.  See the License for the
     specific language governing permissions and limitations
     under the License.
    --->
    +--> 
     
    -SQL is the language of most other relational databases use as query language. It is portable
and easy to learn. But every SQL statement must be executed individually by the database server.

    +PL/pgSQL is a trusted procedural language that is automatically installed and registered
in all HAWQ databases. With PL/pgSQL, you can:
     
    -PL/pgSQL is a loadable procedural language. PL/SQL can do the following:
    +-   Create functions
    +-   Add control structures to the SQL language
    +-   Perform complex computations
    +-   Use all of the data types, functions, and operators defined in SQL
     
    --   create functions
    --   add control structures to the SQL language
    --   perform complex computations
    --   inherit all user-defined types, functions, and operators
    --   be trusted by the server
    +SQL is the language most relational databases use as a query language. While it is portable
and easy to learn, every SQL statement is individually executed by the database server. Your
client application sends each query to the database server, waits for it to be processed,
receives and processes the results, does some computation, then sends further queries to the
server. This back-and-forth requires interprocess communication and incurs network overhead
if your client is on a different host than the HAWQ master.
     
    -You can use functions created with PL/pgSQL with any database that supports built-in
functions. For example, it is possible to create complex conditional computation functions
and later use them to define operators or use them in index expressions.
    +PL/pgSQL does not have these limitations. When creating functions with the PL/pgSQL language,
you can group computation blocks and queries inside the database server, combining the power
of a procedural language and the ease of use of SQL, but with considerable savings of client/server
communication overhead. With PL/pgSQL:
     
    -Every SQL statement must be executed individually by the database server. Your client
application must send each query to the database server, wait for it to be processed, receive
and process the results, do some computation, then send further queries to the server. This
requires interprocess communication and incurs network overhead if your client is on a different
machine than the database server.
    +-   Extra round trips between client and server are eliminated
    +-   Intermediate, and perhaps unneeded, results do not have to be marshaled or transferred
between the server and client
    +-   You avoid multiple rounds of query parsing
    + 
     
    -With PL/pgSQL, you can group a block of computation and a series of queries inside the
database server, thus having the power of a procedural language and the ease of use of SQL,
but with considerable savings of client/server communication overhead.
    +## <a id="plpgsql_structure"></a>PL/pgSQL Function Syntax
     
    --   Extra round trips between client and server are eliminated
    --   Intermediate results that the client does not need do not have to be marshaled or
transferred between server and client
    --   Multiple rounds of query parsing can be avoided
    +PL/pgSQL is a block-structured language. The complete text of a function definition must
be a block, which is defined as:
     
    -This can result in a considerable performance increase as compared to an application
that does not use stored functions.
    +``` sql
    +[ <label> ]
    +[ DECLARE
    +    declarations ]
    +BEGIN
    +    statements
    +END [ label ];
    +```
     
    -PL/pgSQL supports all the data types, operators, and functions of SQL.
    +Each declaration and each statement within a block is terminated by a semicolon. A block
that appears within another block must have a semicolon after `END`, as shown above; however
the final `END` that concludes a function body does not require a semicolon.
    +
    +You can specify all key words and identifiers in mixed upper and lower case. Identifiers
are implicitly converted to lowercase unless double-quoted.
    +
    +PL/pgSQL supports two types of comments. A double dash (`--`) starts a comment that extends
to the end of the line. A `/*` starts a block comment that extends to the next occurrence
of `*/`. Block comments cannot be nested, but you can enclose double dash comments into a
block comment and a double dash can hide the block comment delimiters `/*` and `*/`.
    +
    +This example PL/pgSQL function adds thirteen to an integer:
    +
    +``` sql
    +=> CREATE FUNCTION add_thirteen(i integer) RETURNS integer AS 
    +   $$
    +   DECLARE
    +       incvalue integer := 13;
    +   BEGIN
    +       -- add thirteen to i
    +       RETURN i + incvalue;
    +   END;
    +   $$ LANGUAGE plpgsql;
    +=> SELECT add_thirteen( 11 );
    +    increment 
    +   -----------
    +           24
    +   (1 row)
    +```
     
    -**Note:**  PL/pgSQL is automatically installed and registered in all HAWQ databases.
    +**Note**: Do not to confuse the use of `BEGIN/END` for grouping statements in PL/pgSQL
with the database commands for transaction control. PL/pgSQL's BEGIN/END are only for statement
grouping; they do not start or end a transaction. 
    --- End diff --
    
    Do we need to show an example of using BEGIN/END for transaction management in a block?


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