常用数据库查询判断表和字段是否存在的SQL（如果结果为1表示存在，为0表示不存在）

1、MSSQL Server
表：
SELECT COUNT(*) FROM dbo.sysobjects 
WHERE name= 'table_name';
字段：
SELECT COUNT(*) FROM syscolumns 
WHERE id=object_id(‘table_name’) AND name= 'column_name';
 
2、My SQL
表：
SELECT COUNT(*) FROM information_schema.tables 
WHERE table_name ='table_name';
字段：
SELECT COUNT(*) FROM information_schema.columns 
WHERE table_name ='table_name' AND column_name ='column_name';
 
3、Oracle
表：
SELECT count(*) FROM USER_OBJECTS 
WHERE OBJECT_NAME = 'table_name';
字段：
SELECT COUNT(*) FROM USER_TAB_COLUMNS 
WHERE TABLE_NAME ='table_name' AND column_name ='column_name';
 
4、PostgreSql
表：
SELECT count(*) FROM information_schema.tables 
WHERE table_schema='table_schema' AND table_name ='table_name';
字段：
SELECT count(*) FROM information_schema.columns 
WHERE table_schema='table_schema' AND table_name ='table_name' AND column_name='column_name';