Postgresql base64编码

我需要将db值转换为base64encode.我试过了：

select encode(cast(est_name as text),'base64') from establishments;

它显示错误

[sql]select encode(string(cast(est_name as text)),'base64') from establishments;

[Err] ERROR:  function string(text) does not exist
LINE 1: select encode(string(cast(est_name as text)),'base64') from ...
                      ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

哪里错了？请帮忙.提前致谢

解决方法

编码功能从bytea编码为文本.

select encode(est_name::bytea,'base64') 
from establishments;

http://www.postgresql.org/docs/current/static/functions-binarystring.html#FUNCTIONS-BINARYSTRING-OTHER