first commit for openGauss connector jdbc

docs/documentation/head/statement.md

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+---
+layout: default_docs
+title: Using the Statement or PreparedStatement Interface
+header: Chapter 5. Issuing a Query and Processing the Result
+resource: media
+previoustitle: Chapter 5. Issuing a Query and Processing the Result
+previous: query.html
+nexttitle: Using the ResultSet Interface
+next: resultset.html
+---
+
+The following must be considered when using the `Statement` or `PreparedStatement`
+interface:
+
+* You can use a single `Statement` instance as many times as you want. You could
+	create one as soon as you open the connection and use it for the connection's
+	lifetime. But you have to remember that only one `ResultSet` can exist
+	per `Statement` or `PreparedStatement` at a given time.
+* If you need to perform a query while processing a `ResultSet`, you can simply
+	create and use another `Statement`.
+* If you are using threads, and several are using the database, you must use a
+	separate `Statement` for each thread. Refer to [Chapter 10, *Using the Driver in a Multithreaded or a Servlet Environment*](thread.html)
+	if you are thinking of using threads, as it covers some important points.
+* When you are done using the `Statement` or `PreparedStatement` you should close
+	it.
+* In JDBC, the question mark (`?`) is the placeholder for the positional parameters of a `PreparedStatement`.
+    There are, however, a number of PostgreSQL operators that contain a question mark.
+    To keep such question marks in a SQL statement from being interpreted as positional parameters,
+    use two question marks (`??`) as escape sequence.
+    You can also use this escape sequence in a `Statement`, but that is not required.
+    Specifically only in a `Statement` a single (`?`) can be used as an operator.