数据库SQL优化

Postgres数据库organization表：CREATE TABLE ORGANIZATION( -- 分公司与部门表DWBH INTEGER NOT NULL, -- 部门IDDWMC VARCHAR(50) NOT NULL, --部门名称FGS INTEGER NOT NULL, --分公司IDFGSMC VARCHAR(50) NOT NULL --分公司名称)优化前：select concat(fgsmc,'---',dwmc) as dwmc from organization where fgsmc!=dwmc union all select distinct dwmc from organization where fgsmc=dwmc优化后：select case when fgsmc!=dwmc then concat(fgsmc,'---',dwmc) when fgsmc=dwmc then dwmc end as dwmc from organization