常用数据库查询判断表和字段是否存在的SQL

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';