您缺少 e 就在换行文字之前（对于像c的特殊字符来说是必需的）：

You are missing e right before new line literal (it is required for c-like special chars):

SELECT message,  CASE WHEN length(message) > 100 
THEN  message||e'\n' end as res FROM msg.list_trx

查看 http://www.postgresql.org/ docs / 9.0 / static / sql-syntax-lexical.html

4.1.2.2。带有C样式转义符的字符串常量

4.1.2.2. String Constants with C-Style Escapes

以获取更多信息。