postgres if ，when及判断表是否存在的sql编写

判断表是否存在方法1：

SELECT  case  WHEN   a.cc = THEN  else  END
FROM
(
select  count(*) as cc from pg_class where relname = 'wo'　　　　--wo is table name，pg_class是pg自带的关键字
) as a  

方法2：

用if判断，但有以下条件

The IF statement is part of the default procedural language PL/pgSQL. You need to create a function or execute an ad-hoc statement with the DO command.、

exist使用要求和if一样

DO
$do$
BEGIN
IF (select  count(*) cc from pg_class where relname = 'wo') = 0 --一定要加括号
THEN
   INSERT INTO wo VALUES (2);
ELSE
   INSERT INTO wo VALUES (1);
END IF;
END
$do$

　联合使用select 和insert的方法如下

create table language_ko(Key text,XML text);
insert into Language_ko(key,xml) (select "Key " as key,'<'||"Key"||'>'||"Korean"||'</'||"Key"||'>' as xml  from "centralClient1")