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 =1 THEN 2 else 0 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

?

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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")