Teradata语法错误期望的是名称或Unicode界限标识符或UDFCALLNAME关键字之类的东西）和联合关键字

Question

但是，在我的SQL查询中，我试图将两个表与两个表的结合在一起，但是，每当我运行查询时，我会收到以下错误消息：Teradata语法错误期望像名称或Unicode界定标识符或UDFCALLNAME关键字'） “联合”关键字。以下是查询的片段。是什么原因导致了这个问题，我应该进行什么编辑来解决此问题？

 FROM 
(SELECT RUN_DT, CAST(LOB AS VARCHAR(11)) AS LOB, MBRID, MEDICAID_NBR, CAST(DISEASE_COND AS VARCHAR(50)) AS DISEASE_COND,CAST(DISEASE_COND_NAME AS VARCHAR(100)) AS DISEASE_COND_NAME, CAST(NULL AS VARCHAR(150)) AS HCC_SUBCAT_DESC, PLAN_DIM_CK,
STATE_CODE, GAP_IND1, GAP_IND2, RISK_MODEL, AID, PRO_GENERIC_PRODUCT_DESC, RATE_CELL_DESC, DIAG, DIAG_DESC,
DOS, NDC, NDC_DESC, MEMBER_MONTHS, RISK_SCORE, GAP_PROBABILITY
FROM MEDICAID_CONDITIONS)
        UNION ALL
(SELECT RUN_DT, LOB, MEMBERID AS MBRID,CAST(NULL AS VARCHAR(30)) AS MEDICAID_NBR, DISEASE_COND, CAST(NULL AS VARCHAR(40)) AS DISEASE_COND_NAME,DISEASE_COND_NAME, PLAN_DIM_CK,
STATE_CODE, GAP_IND1, GAP_IND2, CAST(RISK_MODEL AS VARCHAR(20)) AS RISK_MODEL, CAST(NULL AS VARCHAR(20)) AS AID, CAST(NULL AS VARCHAR(72)) AS PRO_GENERIC_PRODUCT_DESC, CAST(NULL AS VARCHAR(72)) AS RATE_CELL_DESC, DIAG, DIAG_DESC,
DOS, NDC, NDC_DESC, MEMBER_MONTHS, RISK_SCORE, GAP_PROBABILITY
FROM MARKETPLACE_CONDITIONS) AS M