sql 链表查询语句

SELECT
    *
FROM
    jcb_t_asset_combo_item AS jtaci
**INNER join** (select pType,pId,(**CASE WHEN ISNULL(pTrustId)** THEN pFundId ELSE pTrustId END) AS choiceId FROM jcb_t_product) AS product ON product.pId = jtaci.itemRelatedProduct
//连接一个查询出结果的表，该查询出来的结果表有三个字段。type，id，choiceId、
其中Choiceid是通过case When 语句进行判断的。得出来的choiceId 在和下面的新生成的表进行连接
INNER JOIN (
    select product_name as pname ,product_id AS detailId ,product_period AS pqixian, product_rate AS pshouyi ,1 as type from jcb_tnonstandardproduct
 union 
select pFundName as pname ,pFundId AS detailId ,dataDate AS pqoxian ,tenThousandBenifitRate AS pshouyi,2 as type from jcb_t_standerproduct_fund
 ) AS detail **ON detail.detailId = product.choiceId** and detail.type=product.pType
//此连接的表也是新生成的，通过union关键字，进行两个不同的类型的字段进行联合。同时与上一个表的choiceId进行对接
WHERE
    jtaci.itemRelatedAssetPack = 2