postgres if ，when及判断表是否存在的sql编写

flyfish 2020年06月13日数据库 604 0

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

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")