docs - add examples for deprecated timestamp format YYYYMMDDHH24MISS.
Add examples to note when migration from GPDB 4,5 to 6
What fails in 6 and some workarounds.
not permit tables <codeph>DISTRIBUTED RANDOMLY</codeph> to have primary keys or unique
indexes. Restoring such a table from a Greenplum 4.3 or 5 backup will cause an error.</li>
<li>Greenplum 6 no longer automatically converts from the deprecated timestamp format
- YYYYMMDDHH24MISS. The format could not be parsed unambiguously in previous Greenplum
- Database releases. You can still specify the YYYYMMDDHH24MISS format in conversion
- functions such as <codeph>to_timestamp</codeph> and <codeph>to_char</codeph> for
- compatibility with other database systems. You can use input formats for converting text
- to date or timestamp values to avoid unexpected results or query execution failures.</li>
+ <codeph>YYYYMMDDHH24MISS</codeph>. The format could not be parsed unambiguously in
+ previous Greenplum Database releases. You can still specify the
+ <codeph>YYYYMMDDHH24MISS</codeph> format in conversion functions such as
+ <codeph>to_timestamp</codeph> and <codeph>to_char</codeph> for compatibility with other
+ database systems. You can use input formats for converting text to date or timestamp
+ values to avoid unexpected results or query execution failures. For example, this
+ <codeph>SELECT</codeph> command returns a timestamp in Greenplum Database 5 and fails in
+ 6.<codeblock>SELECT to_timestamp('20190905140000');</codeblock><p>To convert the string
+ to a timestamp in Greenplum Database 6, you must use a valid format. Both of these
+ commands return a timestamp in Greenplum Database 6. The first example explicitly
+ specifies a timestamp format. The second example uses the string in a format that
+ Greenplum Database
+ recognizes.<codeblock>SELECT to_timestamp('20190905140000','YYYYMMDDHH24MISS');
+SELECT to_timestamp('201909051 40000');</codeblock></p><p>The
+ timestamp issue also applies when you use the <codeph>::</codeph> syntax. In Greenplum
+ Database 6, the first command returns an error. The second command returns a timestamp.
+ <codeblock>SELECT '20190905140000'::timestamp ;
+SELECT '20190905 140000'::timestamp ;</codeblock></p></li>
<li>Creating a table using the <codeph>CREATE TABLE AS</codeph> command in Greenplum 4.3 or
5 could create a table with a duplicate distribution key. The <codeph>gpbackup</codeph>
utility saves the table to the backup using a <codeph>CREATE TABLE</codeph> command that
