SELECT T1.采购单号,T2.物料,T2.采购入库数量,T4.SL,T3.出库数量
FROM AAA A1
INNER JOIN AAB A2 ON A1.ID=T2.ID
LEFT JOIN AAC T3 ON T2.ID=T3.ID
LEFT JOIN (SELECT 条码ID,COUNT(条码ID) [SL] FROM AAD GROUP BY 条码ID) T4 ON T2.条码ID=T4.条码ID
修改一下on 后的数据类型试试呢