Sql 带奇怪别名的子句
我熟悉Sql 带奇怪别名的子句,sql,Sql,我熟悉with条款的作用,但我遇到过这种说法,我不确定该如何理解: WITH H AS (SELECT PS$,HIERY_TYPE,ID$,HIERY_PS$_PARENT,HIERY_TYPE_PARENT,HIERY_ID$_PARENT,LABEL FROM RSPC_HIERARCHY WHERE PS$='SDH' AND HIERY_TYPE LIKE 'STARS%'), H_TREE(XLEVEL, STARS_FAMILY,PS$,HIERY_TYPE,ID$,
with
条款的作用,但我遇到过这种说法,我不确定该如何理解:
WITH
H AS (SELECT PS$,HIERY_TYPE,ID$,HIERY_PS$_PARENT,HIERY_TYPE_PARENT,HIERY_ID$_PARENT,LABEL FROM RSPC_HIERARCHY WHERE PS$='SDH' AND HIERY_TYPE LIKE 'STARS%'),
H_TREE(XLEVEL, STARS_FAMILY,PS$,HIERY_TYPE,ID$,HIERY_PS$_PARENT,HIERY_TYPE_PARENT,HIERY_ID$_PARENT,LABEL) AS
(
SELECT 1 XLEVEL, ID$ STARS_FAMILY , PS$,HIERY_TYPE,ID$,HIERY_PS$_PARENT,HIERY_TYPE_PARENT,HIERY_ID$_PARENT,LABEL FROM H WHERE HIERY_TYPE ='STARS_FAMILY'
UNION ALL
SELECT HT.XLEVEL + 1 XLEVEL, HT.STARS_FAMILY,H.PS$,H.HIERY_TYPE,H.ID$,H.HIERY_PS$_PARENT,H.HIERY_TYPE_PARENT,H.HIERY_ID$_PARENT, H.LABEL
FROM H, H_TREE HT)
特别是,我不理解H_树
别名。括号中的东西的功能是什么?括号中的东西只是别名列名称的列表。我认为create view
支持相同的构造
通常,列名直接取自
select
。但是它们也可以在之前指定为
是,与创建视图
的构造相同!