一个sql的小疑点

求助一个sql的小问题
我做这个查询需求是如果b.contractid=1那么c.contractamount就会等于空或者0，请问各位大神们该怎么改

	SELECT
				b.id,
				b.contractid,
				b.prjname,
				b.prjmanager,
				b.budgetamount,
				b.ownerorg,
				b.jlorg,
				b.settleprinciple,
				b.remark,
				b.createmanid,
				b.createdatetime,
				b.relevance,
				b.createorgid,
				c.contractamount
			FROM projbudge as b 
			cross join projcostaccouting as c 
			WHERE 1=1 and b.contractid=1

------解决思路----------------------

SELECT
            b.id,
            b.contractid,
            b.prjname,
            b.prjmanager,
            b.budgetamount,
            b.ownerorg,
            b.jlorg,
            b.settleprinciple,
            b.remark,
            b.createmanid,
            b.createdatetime,
            b.relevance,
            b.createorgid,
            case when b.contractid=1 then c.contractamount else 0 end as contractamount 
        FROM projbudge as b 
        cross join projcostaccouting as c

 
------解决思路----------------------
用CASE处理就可以啦，要NULL 要0都做得到

或许应该直接左连接

SELECT
            b.id,
            b.contractid,
            b.prjname,
            b.prjmanager,
            b.budgetamount,
            b.ownerorg,
            b.jlorg,
            b.settleprinciple,
            b.remark,
            b.createmanid,
            b.createdatetime,
            b.relevance,
            b.createorgid,
            c.contractamount
        FROM projbudge as b 
        LEFT join projcostaccouting as c ON b.contractid=1 and 其他连接条件