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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